Be advised, this is a VERY long post (split into two), but contains information some of the more commonly asked information that’s helpful to the new (or prospective new) 6.5 owner. Reading this post (as well as the other posts marked “New Members Read This” in the 6.5 forum at the beginning of your 6.5 experience can save you a lot of hassle and money.
So you just bought a 6.5TD, or are thinking of buying one - Where to start?!
Welcome to the world of the GM 6.5 Turbo Diesel! First off, You’ve found the right forum - the Diesel Place 6.5 forum is one of the busiest on the ‘Net, and is full of not only people like yourself (who are new to the 6.5 and wanting to learn more) but also countless other members who are extremely knowledgeable about this engine and know it like the back of their hand. Nowhere else will you find such a vast base of knowledge for free.
Setting out, here are two very important things to remember:
1/ The GM 6.5 Turbo Diesel has received a bad reputation during it’s lifespan. Unfortunately much of this comes from people who simply don’t treat the engine correctly and suffered the consequences. Unlike other diesel engines, the 6.5 does not tolerate abuse (or lack of maintenance) well, and frequently people who beat on them were the first to complain loudly about it when they experienced issues. The bad reputation, even though it was not really warranted, started here. The 6.5 is NOT a “Disaster” of an engine like some would have you believe...but it is important that you know it’s quirks and limitations - this thread will help you with that.
2/ Diesel engines are an enigma to many mechanics, especially those not familiar with diesels in general. The 6.5 is even more of an enigma, and the plain truth is that most mechanics (even some diesel mechanics!) simply know little to nothing about it...and you MUST know this engine to understand it’s intricacies and oddities. Don’t fall into the trap of letting a clueless mechanic spend hundreds (or thousands) of your dollars playing the “replace this part and see what happens” game when in reality all that was necessary was a $50 part and a half hour or labor in your driveway. It pays to educate yourself about the engine, and ask for help here before resorting to a mechanic - the 6.5 is one of the simplest diesel engines on the roads today, and if you have basic mechanics tools and aren’t afraid to get dirty, you can do most of your own maintenance and repairs easily. Knowledge is key, and you may be surprised to find more of it here than you will at your local repair facility!
Haven’t bought a truck with a 6.5 in it yet? As mentioned, the 6.5 suffered a lot of abuse at the hands of less than knowledgeable owners, so it’s important to make SURE you are not buying a truck that has a sick engine to begin with - always start by reading the “Purchasing a 6.5” thread located here:
FAQ: Purchasing a 6.5L Diesel - Diesel Place : Chevrolet and GMC Diesel Truck Forums
Do NOT buy a truck that fails any of the more serious/major tests in the thread above. There are plenty of 6.5-equipped trucks out there and if the engine in the one you are looking for is sick, walk away and find a healthy one instead! Minor things can be fixed, but major engine issues, especially on diesel engines, can sometimes be costly to repair.
If you’ve already made the jump, you have some homework to do in order to make your 6.5 experience a pleasant one. With that said, let’s get started!
- What’s the PMD/FSD I keep reading about? What’s it do, and why should I “relocate” it?
There are countless FSD-related threads right here in the 6.5 forum so it’s very worthwhile searching for the term “PMD” in the 6.5 forum to read up on the potential issues, even if you aren’t (yet) experiencing any yourself, but here’s the basics.
If you have a 6.5 with an electronic DS4 Injection pump (1994 and newer), you have an FSD. They commonly fail due to their location (and heat) resulting in stalling, hesitation, and eventual stranding.
The DS4 injection pump, like the 6.5 itself earned a much-maligned reputation for being “Junk”. Although in its early years it did have some problems (which are covered under an 11-year extended warranty by GM) in many cases the Injection Pump’s bad reputation came as a result of failed FSD units, not the pump itself. Unfortunately, for those who took their vehicles back to GM and found themselves out of warranty coverage, it was likely a very expensive experience.
Worse yet, many mechanics with little to no diesel (or 6.5) experience automatically fingered the entire injection pump (at a replacement cost of >$1000) when in reality the pump itself was fine, but only the (much less costly) FSD unit had failed!
The FSD (Fuel supply driver) is more commonly referred to here at the Diesel Place forum as the “PMD”, or “Pump mounted driver”. It’s a small black box, about the size of a deck of cards mounted on the front of the injection pump. The injection pump itself is located under the intake manifold, which in turn is located under the “Turbo Power” plastic trim piece on top of the engine.
Assuming the PMD is in its stock location it’s a bit out of the way, but You CAN see it if you look closely between the arms of the intake manifold - once you the plastic “Turbo Power” cover off (which you may want to throw away, all it does is block heat from escaping!) you will be able to see it if you look closely with a flashlight - you may see the words “Stanadyne” printed on the front of the module and there will be a single wiring harness plugged into it.
Don’t be surprised to see that the previous owner has already moved the PMD - you may find it (on an extension cord) mounted on the intake manifold, or (ideally) out of the engine compartment completely. If you see the PMD module in its stock location but nothing appears to be plugged into it, it’s been relocated already - follow the nearby cord and you should find it if it’s not already completely obvious.
The PMD module is the brain that tells the injection pump when to fire fuel into the cylinders. Without it, your truck won’t run, and when it begins to fail the problems can range from hesitation to random stalls (usually when hot), to complete no-start situations.
This module, when mounted in its stock location, fails all too frequently. Far too many 6.5 owners have suffered the fate of a failed PMD, and if you take it to a repair facility you can end up paying $500 or more to get it fixed. It need not be that expensive, and putting a new module back in its stock location (which is what many shops will do!) is only asking to experience the same failure again within a year or two, often less.
Why does it fail? HEAT. Although GM’s plan was for the injection pump itself to act as a heat sink (and the fuel flowing through it to cool it further) the simple reality is that it didn’t work - this area was too hot and simply cooks the module, especially when you shut your engine off after driving and it gets heat soaked. Heat is a killer of the PMD!
So, if you just bought a 6.5-equipped vehicle and discover the PMD is still in its stock location .....you really should relocate it. Look at the supporting vendors here and you will find lots of “Remote mount PMD kits” available. You will need an extension harness, a PMD cooler (ESSENTIAL!) and if you are experiencing the symptoms of a failed PMD, a new PMD itself. You can get ALL of this (Cooler, wiring, and replacement PMD) for somewhere in the $500 range, so don’t get sucked into paying $500+ at a dealer or diesel shop for a stock replacement PM alone which won’t include a cooler or extension cable.
We appreciate it if you make your purchase from one of our supporting vendors, as mentioned - remember, our vendors are what keep Diesel Place free for you and I!
Simply visit this forum (click) to find a vendor that stocks the PMD kit. It's easy!
So... Ideally, you want to get the whole PMD assembly out of the engine compartment - some kits are designed to be mounted on the intake manifold or elsewhere under the hood, and although this is better than the stock location, it is still not perfect - I myself had a cooler mounted on the intake manifold and it cooked after 3 years, almost stranding me in the process.
Many people mount them behind the front bumper (in one of the “nostrils), or beside the oil cooler in front of the grille itself. The module is weatherproof (as is the connector) so you can mount it almost anywhere that it will get good airflow and be protected from impact damage.
A cooler attached directly to the PMD is ESSENTIAL! The PMD itself generates a lot of heat and testing has shown that a PMD operated without a heat sink will cook itself in less than 5 minutes, so simply danging it by its wire or zip-tying it in a good airflow area will not work. A good heat sink will take the heat generated and dissipate it to air - obviously, this means the PMD and cooler need to be located in an area with adequate airflow, to begin with, hence the bumper or grille locations.
When mounting the PMD to a cooler it’s also essential that a good heat-transfer paste be used - this is easily available at any computer store (and is typically included with many PMD cooler kits) - its function is to aid the transfer of heat from the module to the cooler. Without it, heat transfer will not be ideal and you may shorten the lifespan of the PMD.
The key is that ANYWHERE else is better than the stock location. Buy the longest extension cord you can (or solder your own!) and mount it somewhere else...ANYWHERE else than the stock location. Your PMD (and wallet) will thank you, and you probably will never have to worry about PMD failure (and being stranded) ever again.
And lastly, a spare PMD in your glove box is always a wise idea for a 6.5 owner, especially if you tow or travel long distances. A $50 “used but tested good” one from eBay is a worthwhile investment as a spare - it could rescue you in a pinch!
So, the moral of the story? If you just got a new 6.5 and the PMD is in the stock location, relocate it. Most people opt to just buy a second PMD and leave the factory one in its current location - removing it requires removal of the intake manifold and is often more hassle than it’s worth, especially when all you’re going to do is throw it in the garbage anyways. Yes, it’s a few hundred dollars of investment, but ask yourself if being stranded in the middle of the night (or on a deserted road) plus the cost of the tow truck is worth the savings. If your PMD is in its stock location it WILL eventually cause you grief - head it off at the pass!
Without a doubt, the PMD (and its related issues) generate the most posts in the Diesel Place 6.5 forum, so before making a new post on the subject be SURE to do a search for “PMD” and read about the issue. Of course, if you need help, make a new post - we’re a friendly bunch and will be glad to help diagnose your issue.
- What’s the deal with the harmonic balancer on the 6.5 - why is everybody freaking out about it?
The harmonic balancer (and sister pulley attached to it) is an essential piece of equipment on the 6.5, and it’s also a part that is commonly failed (or failing) without anyone knowing about it since it often doesn’t have any blatant symptoms except to the tuned ear. However, operating the engine with this essential (yet simple) piece of equipment is like playing Russian roulette with your engine - a failed harmonic balancer assembly can BREAK YOUR CRANKSHAFT!
Broken Crankshaft = Trashed Engine.
The balancer assembly takes the harmonic vibrations that the engine creates and “dampens” them. The crankshaft on the 6.5 is a known weak spot of the engine and these harmonics can (and often will) eventually cause crankshaft failure. Many scrapped 6.5s you may see in the scrapyards will have suffered crank failure due to this simple (and relatively inexpensive) part having been failed and not replaced.
The balancer itself is basically a big chunk of metal with a rubber ring in the middle. This ring should be fully intact - no cracks, no missing chunks, or no deformations. The pulley that attaches to the harmonic balancer also has a rubber ring between the inner and outer races and even more often than the balancer itself, this rubber fails - often without much indication, often just a hairline crack and some noise.
Symptoms of a failed pulley range from a loud clatter through the radiator (audible clearly from the front of the truck when running) to a “clunk” moments after the engine is shut off. Visibly, you may also see a shimmy on the pulley or harmonic balancer.
If the pulley has failed, in addition to the small crack in the rubber running the entire circumference of the pulley, you will often see impact marks on the stop-pins that prevent the inner and outer rings from freewheeling if the rubber fails - in extreme cases, the inner ring actually impacts the bolt heads themselves leading to further damage. Inspect carefully!
A complete circumference crack or giant missing pieces of the rubber rings on either the HB itself or the pulley is an indication that it has failed and requires immediate replacement.
Both the pulley and balancer itself are easily inspected from underneath the truck - simply look at the nose of the crankshaft and carefully inspect. If you are unsure, ask someone who is familiar with the 6.5 to inspect it for you.
INSPECTION AND IMMEDIATE REPLACEMENT OF A FAILED BALANCER OR PULLEY ARE ABSOLUTELY ESSENTIAL! Many people recommend not even starting your truck if you find either the HB or pulley has failed - that 5-mile trip to the auto parts store (even at low RPM) could very well be the trip that snaps your crank. Treat your harmonic balancer and pulley with the utmost respect, it’s a major key to a long-lived 6.5!
If you need help or guidance on inspection, simply make a post here in the Diesel Place 6.5 forum (Attach pictures if possible), or search for previous posts on the subject using the “Search” function - there are plenty of threads dedicated to the HB, as well as many vendors here on the forum that offer some intriguing replacement options such as the “Fluid Damper”.
- What oil should I use? Can I use cheap 10W30 instead of expensive “Diesel” engine oil?
NO! Diesels (ALL diesels, not only the 6.5) require specially rated oils that can deal with the abuse that diesel engines dish out. Gasoline-rated oils are not only of inadequate viscosity (thickness) for a diesel but also do not have the formulation to deal with the ash and other impurities (not to mention heat) that a diesel engine produces.
If you are prospectively looking at a diesel truck (6.5 or not) make SURE that the previous owner has used proper diesel oil for the entire lifespan of the engine - if he hasn’t, run away - run away fast..
If you are the new owner of a 6.5-equipped truck, use diesel oil - never be tempted to buy automotive-rated oils. Diesel engines that are fed a diet of gasoline-rated oils typically suffer from premature wear - extreme blow-by (failing piston rings) and other issues are common. Repair is extremely expensive.
Synthetic versus Dinosaur (regular) oil is a huge topic of debate for all diesel engine owners, although all the 6.5 requires (by the letter of the manual) is a oil rated to CG-4 (or better) standards. Basically all diesel engine oils you will find for sale today meet (and typically exceed) these ratings.
Synthetic oils have benefits but also come at a much steeper cost. You’re choice - a simple Google search will turn up plenty of debate on the subject.
When changing the oil on the 6.5 don’t be surprised to see that your brand new engine oil is jet-black the second you re-start your engine. This is common on most diesel engines (not only the 6.5) due to the fact that the oil cooler typically holds a lot of oil that cannot be changed. Despite being black almost immediately the engine still benefits from the oil change, so don’t feel it’s in vain - change your oil regularly!
- My 6.5 is dripping oil from the oil cooler lines.
This is an extremely common 6.5 issue - the stock GM lines are junk and will leak often within a year of installation. Many aftermarket lines that are manufactured to be "direct replacements" are little better, and will leak the same as the factory lines, not to mention that they utilize the same poor connections as the stock lines. (Read on)
However, the oil cooler is essential on the 6.5 so don’t be tempted to simply bypass or remove it! You'll cook your engine, eventually...no matter what any mechanic may say otherwise.
Extreme care should be taken to keep close tabs on the health of these lines - the 6.5 will continue to run even if it loses ALL of its oil due to a blown oil cooler line, and you WILL seize your engine if this occurs. Not only are the factory lines prone to splitting (aside from their constant leaking), but they also utilize an absolutely terrible connection method to the engine itself, relying on several small clips to hold the lines into the fittings on the engine block. These tiny clips corrode as the years pass, and if/when one of them corrodes and rusts to the point where it breaks, the clip can fall out, leaving nothing holding the line into the block fitting. The rest is history when the line blows out - if you don't immediately notice it (and many don't, unfortunately) your engine will run out of oil and seize, stranding you on the side of the road.
Replacement of the factory lines is an almost essential modification for the serious 6.5 owner and there are a variety of aftermarket kits available (For about $250) that use much stronger and more durable braided lines. Several of our Supporting Vendors here at dieselplace, most notably Lubrication Specialists, sells these kits directly. It will not only solve the leaky factory lines (no more mess on your driveway), but will also ensure that you don’t accidentally run your engine dry (and seize it) if one of the factory lines ever blows without your knowledge.
If your factory lines seem healthy (and inspect them CAREFULLY!), at the very least most people recommend replacing the tiny clips at the fittings of the lines to the engine block. Remove the old (possibly corroded and weakened) clips and replace them with new ones. It's the absolute cheapest insurance you will ever invest in for your 6.5, short of a complete replacement of the lines with the aforementioned kit.
- I hear lots of stories of injection pump problems on the 6.5. What should I do to protect it?
The Injection Pump (IP) on the 6.5 was designed before the introduction of Ultra Low Sulphur Diesel, or ULSD. ULSD has a much lower “slipperiness” (lubricity) than the fuel that the 6.5 injection pump was designed for.
The long and the short of this is that the “dryness” of ULSD can cause premature wear (and eventual) failure of the IP at a fairly significant cost. Again, the 6.5 garnered a bad reputation with many owners due to IP failures, many of which could have been avoided. Yes, as mentioned earlier, some DS4 model injection pumps did have issues that caused the failure (lubricity aside) but chances are if you just bought a 6.5 equipped truck (with the DS4 electronic injection pump) the previous owner has already addressed the issue, either by replacing the pump himself or having it replaced under warranty. Let’s assume (and hope) you’re IP is still healthy - keep it that way - Buy a quality lubricity additive and use it religiously with each and every fill-up.
Some people use simple 2-stroke oil, and others use brand-name additives such as the genuine Stanadyne options, or other off-the-shelf additives.
What additive should you use? Some time ago there was an in-depth study done with the results posted in this thread:
Lubricity Additive Study Results - Diesel Place : Chevrolet and GMC Diesel Truck Forums
It’s important to treat your IP right to ensure a long life. Maintained correctly with proper lubricity the IP on the 6.5 is typically trouble free contrary to many of the stories of dread you might have read about. Again, its bad reputation is not really deserved but was a direct result of people unwittingly hurting the IP because of lack of understanding about the effects of the introduction of ULSD.
- What’s the Lift Pump? What’s it do? What happens if it quits working?
The lift pump on the 6.5 is another essential piece of equipment, but also one that presents few (or sometimes no) symptoms if failed and can lead to issues.
The lift pump is mounted to the frame rail on the driver's side of the truck. It is commonly mistaken for (and looks somewhat like) a fuel filter except if you look closely you will see two wires leading to it. It’s not a filter at all!
This pump draws fuel from the fuel tank and feeds the injection pump at about 7PSI.
If this pump fails, the problem is that often the truck will continue running, sometimes with no symptoms. The big issue with this is that the injection pump was not designed to “suck” fuel all the way from the fuel pump and as a result being forced to do so can result in IP problems down the road.
When symptoms do present themselves, they are typically a lack of power (fuel starvation) or difficult starts (Fuel draining back to the tank from IP and not being primed at key-on). Occasionally the engine will not start at all as is common with an already worn or sick injection pump which no longer has the strength to “suck” from the tank itself. Often, by the time these symptoms present themselves the damage to your IP may already have been done.
Diagnosis is fairly easy - when you turn the key on (without starting the engine) you should be able to hear the pump run for a second or three. Secondly (and more determining) by opening the water-drain tap (located on the engine near the alternator) you should be able to obtain a steady flow of fuel if opened and the ignition key cycled (You may want 2 people for this job...).
If you open this tap but do NOT get a strong flow of fuel with the key cycled to the “ON” position, your lift pump may not be functional. Although it’s technically safe to drive in this condition, it’s not wise....get it fixed - your IP will thank you and you will potentially save yourself the hassle and expense of an injection pump replacement down the road.
Again, If you need help, simply make a post here in the Diesel Place 6.5 forum, or search for previous posts on the subject using the “Search” function using the term “Lift Pump” specifically in the 6.5 forum.
(Continued in response below....)
So you just bought a 6.5TD, or are thinking of buying one - Where to start?!
Welcome to the world of the GM 6.5 Turbo Diesel! First off, You’ve found the right forum - the Diesel Place 6.5 forum is one of the busiest on the ‘Net, and is full of not only people like yourself (who are new to the 6.5 and wanting to learn more) but also countless other members who are extremely knowledgeable about this engine and know it like the back of their hand. Nowhere else will you find such a vast base of knowledge for free.
Setting out, here are two very important things to remember:
1/ The GM 6.5 Turbo Diesel has received a bad reputation during it’s lifespan. Unfortunately much of this comes from people who simply don’t treat the engine correctly and suffered the consequences. Unlike other diesel engines, the 6.5 does not tolerate abuse (or lack of maintenance) well, and frequently people who beat on them were the first to complain loudly about it when they experienced issues. The bad reputation, even though it was not really warranted, started here. The 6.5 is NOT a “Disaster” of an engine like some would have you believe...but it is important that you know it’s quirks and limitations - this thread will help you with that.
2/ Diesel engines are an enigma to many mechanics, especially those not familiar with diesels in general. The 6.5 is even more of an enigma, and the plain truth is that most mechanics (even some diesel mechanics!) simply know little to nothing about it...and you MUST know this engine to understand it’s intricacies and oddities. Don’t fall into the trap of letting a clueless mechanic spend hundreds (or thousands) of your dollars playing the “replace this part and see what happens” game when in reality all that was necessary was a $50 part and a half hour or labor in your driveway. It pays to educate yourself about the engine, and ask for help here before resorting to a mechanic - the 6.5 is one of the simplest diesel engines on the roads today, and if you have basic mechanics tools and aren’t afraid to get dirty, you can do most of your own maintenance and repairs easily. Knowledge is key, and you may be surprised to find more of it here than you will at your local repair facility!
Haven’t bought a truck with a 6.5 in it yet? As mentioned, the 6.5 suffered a lot of abuse at the hands of less than knowledgeable owners, so it’s important to make SURE you are not buying a truck that has a sick engine to begin with - always start by reading the “Purchasing a 6.5” thread located here:
FAQ: Purchasing a 6.5L Diesel - Diesel Place : Chevrolet and GMC Diesel Truck Forums
Do NOT buy a truck that fails any of the more serious/major tests in the thread above. There are plenty of 6.5-equipped trucks out there and if the engine in the one you are looking for is sick, walk away and find a healthy one instead! Minor things can be fixed, but major engine issues, especially on diesel engines, can sometimes be costly to repair.
If you’ve already made the jump, you have some homework to do in order to make your 6.5 experience a pleasant one. With that said, let’s get started!
- What’s the PMD/FSD I keep reading about? What’s it do, and why should I “relocate” it?
There are countless FSD-related threads right here in the 6.5 forum so it’s very worthwhile searching for the term “PMD” in the 6.5 forum to read up on the potential issues, even if you aren’t (yet) experiencing any yourself, but here’s the basics.
If you have a 6.5 with an electronic DS4 Injection pump (1994 and newer), you have an FSD. They commonly fail due to their location (and heat) resulting in stalling, hesitation, and eventual stranding.
The DS4 injection pump, like the 6.5 itself earned a much-maligned reputation for being “Junk”. Although in its early years it did have some problems (which are covered under an 11-year extended warranty by GM) in many cases the Injection Pump’s bad reputation came as a result of failed FSD units, not the pump itself. Unfortunately, for those who took their vehicles back to GM and found themselves out of warranty coverage, it was likely a very expensive experience.
Worse yet, many mechanics with little to no diesel (or 6.5) experience automatically fingered the entire injection pump (at a replacement cost of >$1000) when in reality the pump itself was fine, but only the (much less costly) FSD unit had failed!
The FSD (Fuel supply driver) is more commonly referred to here at the Diesel Place forum as the “PMD”, or “Pump mounted driver”. It’s a small black box, about the size of a deck of cards mounted on the front of the injection pump. The injection pump itself is located under the intake manifold, which in turn is located under the “Turbo Power” plastic trim piece on top of the engine.
Assuming the PMD is in its stock location it’s a bit out of the way, but You CAN see it if you look closely between the arms of the intake manifold - once you the plastic “Turbo Power” cover off (which you may want to throw away, all it does is block heat from escaping!) you will be able to see it if you look closely with a flashlight - you may see the words “Stanadyne” printed on the front of the module and there will be a single wiring harness plugged into it.
Don’t be surprised to see that the previous owner has already moved the PMD - you may find it (on an extension cord) mounted on the intake manifold, or (ideally) out of the engine compartment completely. If you see the PMD module in its stock location but nothing appears to be plugged into it, it’s been relocated already - follow the nearby cord and you should find it if it’s not already completely obvious.
The PMD module is the brain that tells the injection pump when to fire fuel into the cylinders. Without it, your truck won’t run, and when it begins to fail the problems can range from hesitation to random stalls (usually when hot), to complete no-start situations.
This module, when mounted in its stock location, fails all too frequently. Far too many 6.5 owners have suffered the fate of a failed PMD, and if you take it to a repair facility you can end up paying $500 or more to get it fixed. It need not be that expensive, and putting a new module back in its stock location (which is what many shops will do!) is only asking to experience the same failure again within a year or two, often less.
Why does it fail? HEAT. Although GM’s plan was for the injection pump itself to act as a heat sink (and the fuel flowing through it to cool it further) the simple reality is that it didn’t work - this area was too hot and simply cooks the module, especially when you shut your engine off after driving and it gets heat soaked. Heat is a killer of the PMD!
So, if you just bought a 6.5-equipped vehicle and discover the PMD is still in its stock location .....you really should relocate it. Look at the supporting vendors here and you will find lots of “Remote mount PMD kits” available. You will need an extension harness, a PMD cooler (ESSENTIAL!) and if you are experiencing the symptoms of a failed PMD, a new PMD itself. You can get ALL of this (Cooler, wiring, and replacement PMD) for somewhere in the $500 range, so don’t get sucked into paying $500+ at a dealer or diesel shop for a stock replacement PM alone which won’t include a cooler or extension cable.
We appreciate it if you make your purchase from one of our supporting vendors, as mentioned - remember, our vendors are what keep Diesel Place free for you and I!
Simply visit this forum (click) to find a vendor that stocks the PMD kit. It's easy!
So... Ideally, you want to get the whole PMD assembly out of the engine compartment - some kits are designed to be mounted on the intake manifold or elsewhere under the hood, and although this is better than the stock location, it is still not perfect - I myself had a cooler mounted on the intake manifold and it cooked after 3 years, almost stranding me in the process.
Many people mount them behind the front bumper (in one of the “nostrils), or beside the oil cooler in front of the grille itself. The module is weatherproof (as is the connector) so you can mount it almost anywhere that it will get good airflow and be protected from impact damage.
A cooler attached directly to the PMD is ESSENTIAL! The PMD itself generates a lot of heat and testing has shown that a PMD operated without a heat sink will cook itself in less than 5 minutes, so simply danging it by its wire or zip-tying it in a good airflow area will not work. A good heat sink will take the heat generated and dissipate it to air - obviously, this means the PMD and cooler need to be located in an area with adequate airflow, to begin with, hence the bumper or grille locations.
When mounting the PMD to a cooler it’s also essential that a good heat-transfer paste be used - this is easily available at any computer store (and is typically included with many PMD cooler kits) - its function is to aid the transfer of heat from the module to the cooler. Without it, heat transfer will not be ideal and you may shorten the lifespan of the PMD.
The key is that ANYWHERE else is better than the stock location. Buy the longest extension cord you can (or solder your own!) and mount it somewhere else...ANYWHERE else than the stock location. Your PMD (and wallet) will thank you, and you probably will never have to worry about PMD failure (and being stranded) ever again.
And lastly, a spare PMD in your glove box is always a wise idea for a 6.5 owner, especially if you tow or travel long distances. A $50 “used but tested good” one from eBay is a worthwhile investment as a spare - it could rescue you in a pinch!
So, the moral of the story? If you just got a new 6.5 and the PMD is in the stock location, relocate it. Most people opt to just buy a second PMD and leave the factory one in its current location - removing it requires removal of the intake manifold and is often more hassle than it’s worth, especially when all you’re going to do is throw it in the garbage anyways. Yes, it’s a few hundred dollars of investment, but ask yourself if being stranded in the middle of the night (or on a deserted road) plus the cost of the tow truck is worth the savings. If your PMD is in its stock location it WILL eventually cause you grief - head it off at the pass!
Without a doubt, the PMD (and its related issues) generate the most posts in the Diesel Place 6.5 forum, so before making a new post on the subject be SURE to do a search for “PMD” and read about the issue. Of course, if you need help, make a new post - we’re a friendly bunch and will be glad to help diagnose your issue.
- What’s the deal with the harmonic balancer on the 6.5 - why is everybody freaking out about it?
The harmonic balancer (and sister pulley attached to it) is an essential piece of equipment on the 6.5, and it’s also a part that is commonly failed (or failing) without anyone knowing about it since it often doesn’t have any blatant symptoms except to the tuned ear. However, operating the engine with this essential (yet simple) piece of equipment is like playing Russian roulette with your engine - a failed harmonic balancer assembly can BREAK YOUR CRANKSHAFT!
Broken Crankshaft = Trashed Engine.
The balancer assembly takes the harmonic vibrations that the engine creates and “dampens” them. The crankshaft on the 6.5 is a known weak spot of the engine and these harmonics can (and often will) eventually cause crankshaft failure. Many scrapped 6.5s you may see in the scrapyards will have suffered crank failure due to this simple (and relatively inexpensive) part having been failed and not replaced.
The balancer itself is basically a big chunk of metal with a rubber ring in the middle. This ring should be fully intact - no cracks, no missing chunks, or no deformations. The pulley that attaches to the harmonic balancer also has a rubber ring between the inner and outer races and even more often than the balancer itself, this rubber fails - often without much indication, often just a hairline crack and some noise.
Symptoms of a failed pulley range from a loud clatter through the radiator (audible clearly from the front of the truck when running) to a “clunk” moments after the engine is shut off. Visibly, you may also see a shimmy on the pulley or harmonic balancer.
If the pulley has failed, in addition to the small crack in the rubber running the entire circumference of the pulley, you will often see impact marks on the stop-pins that prevent the inner and outer rings from freewheeling if the rubber fails - in extreme cases, the inner ring actually impacts the bolt heads themselves leading to further damage. Inspect carefully!
A complete circumference crack or giant missing pieces of the rubber rings on either the HB itself or the pulley is an indication that it has failed and requires immediate replacement.
Both the pulley and balancer itself are easily inspected from underneath the truck - simply look at the nose of the crankshaft and carefully inspect. If you are unsure, ask someone who is familiar with the 6.5 to inspect it for you.
INSPECTION AND IMMEDIATE REPLACEMENT OF A FAILED BALANCER OR PULLEY ARE ABSOLUTELY ESSENTIAL! Many people recommend not even starting your truck if you find either the HB or pulley has failed - that 5-mile trip to the auto parts store (even at low RPM) could very well be the trip that snaps your crank. Treat your harmonic balancer and pulley with the utmost respect, it’s a major key to a long-lived 6.5!
If you need help or guidance on inspection, simply make a post here in the Diesel Place 6.5 forum (Attach pictures if possible), or search for previous posts on the subject using the “Search” function - there are plenty of threads dedicated to the HB, as well as many vendors here on the forum that offer some intriguing replacement options such as the “Fluid Damper”.
- What oil should I use? Can I use cheap 10W30 instead of expensive “Diesel” engine oil?
NO! Diesels (ALL diesels, not only the 6.5) require specially rated oils that can deal with the abuse that diesel engines dish out. Gasoline-rated oils are not only of inadequate viscosity (thickness) for a diesel but also do not have the formulation to deal with the ash and other impurities (not to mention heat) that a diesel engine produces.
If you are prospectively looking at a diesel truck (6.5 or not) make SURE that the previous owner has used proper diesel oil for the entire lifespan of the engine - if he hasn’t, run away - run away fast..
If you are the new owner of a 6.5-equipped truck, use diesel oil - never be tempted to buy automotive-rated oils. Diesel engines that are fed a diet of gasoline-rated oils typically suffer from premature wear - extreme blow-by (failing piston rings) and other issues are common. Repair is extremely expensive.
Synthetic versus Dinosaur (regular) oil is a huge topic of debate for all diesel engine owners, although all the 6.5 requires (by the letter of the manual) is a oil rated to CG-4 (or better) standards. Basically all diesel engine oils you will find for sale today meet (and typically exceed) these ratings.
Synthetic oils have benefits but also come at a much steeper cost. You’re choice - a simple Google search will turn up plenty of debate on the subject.
When changing the oil on the 6.5 don’t be surprised to see that your brand new engine oil is jet-black the second you re-start your engine. This is common on most diesel engines (not only the 6.5) due to the fact that the oil cooler typically holds a lot of oil that cannot be changed. Despite being black almost immediately the engine still benefits from the oil change, so don’t feel it’s in vain - change your oil regularly!
- My 6.5 is dripping oil from the oil cooler lines.
This is an extremely common 6.5 issue - the stock GM lines are junk and will leak often within a year of installation. Many aftermarket lines that are manufactured to be "direct replacements" are little better, and will leak the same as the factory lines, not to mention that they utilize the same poor connections as the stock lines. (Read on)
However, the oil cooler is essential on the 6.5 so don’t be tempted to simply bypass or remove it! You'll cook your engine, eventually...no matter what any mechanic may say otherwise.
Extreme care should be taken to keep close tabs on the health of these lines - the 6.5 will continue to run even if it loses ALL of its oil due to a blown oil cooler line, and you WILL seize your engine if this occurs. Not only are the factory lines prone to splitting (aside from their constant leaking), but they also utilize an absolutely terrible connection method to the engine itself, relying on several small clips to hold the lines into the fittings on the engine block. These tiny clips corrode as the years pass, and if/when one of them corrodes and rusts to the point where it breaks, the clip can fall out, leaving nothing holding the line into the block fitting. The rest is history when the line blows out - if you don't immediately notice it (and many don't, unfortunately) your engine will run out of oil and seize, stranding you on the side of the road.
Replacement of the factory lines is an almost essential modification for the serious 6.5 owner and there are a variety of aftermarket kits available (For about $250) that use much stronger and more durable braided lines. Several of our Supporting Vendors here at dieselplace, most notably Lubrication Specialists, sells these kits directly. It will not only solve the leaky factory lines (no more mess on your driveway), but will also ensure that you don’t accidentally run your engine dry (and seize it) if one of the factory lines ever blows without your knowledge.
If your factory lines seem healthy (and inspect them CAREFULLY!), at the very least most people recommend replacing the tiny clips at the fittings of the lines to the engine block. Remove the old (possibly corroded and weakened) clips and replace them with new ones. It's the absolute cheapest insurance you will ever invest in for your 6.5, short of a complete replacement of the lines with the aforementioned kit.
- I hear lots of stories of injection pump problems on the 6.5. What should I do to protect it?
The Injection Pump (IP) on the 6.5 was designed before the introduction of Ultra Low Sulphur Diesel, or ULSD. ULSD has a much lower “slipperiness” (lubricity) than the fuel that the 6.5 injection pump was designed for.
The long and the short of this is that the “dryness” of ULSD can cause premature wear (and eventual) failure of the IP at a fairly significant cost. Again, the 6.5 garnered a bad reputation with many owners due to IP failures, many of which could have been avoided. Yes, as mentioned earlier, some DS4 model injection pumps did have issues that caused the failure (lubricity aside) but chances are if you just bought a 6.5 equipped truck (with the DS4 electronic injection pump) the previous owner has already addressed the issue, either by replacing the pump himself or having it replaced under warranty. Let’s assume (and hope) you’re IP is still healthy - keep it that way - Buy a quality lubricity additive and use it religiously with each and every fill-up.
Some people use simple 2-stroke oil, and others use brand-name additives such as the genuine Stanadyne options, or other off-the-shelf additives.
What additive should you use? Some time ago there was an in-depth study done with the results posted in this thread:
Lubricity Additive Study Results - Diesel Place : Chevrolet and GMC Diesel Truck Forums
It’s important to treat your IP right to ensure a long life. Maintained correctly with proper lubricity the IP on the 6.5 is typically trouble free contrary to many of the stories of dread you might have read about. Again, its bad reputation is not really deserved but was a direct result of people unwittingly hurting the IP because of lack of understanding about the effects of the introduction of ULSD.
- What’s the Lift Pump? What’s it do? What happens if it quits working?
The lift pump on the 6.5 is another essential piece of equipment, but also one that presents few (or sometimes no) symptoms if failed and can lead to issues.
The lift pump is mounted to the frame rail on the driver's side of the truck. It is commonly mistaken for (and looks somewhat like) a fuel filter except if you look closely you will see two wires leading to it. It’s not a filter at all!
This pump draws fuel from the fuel tank and feeds the injection pump at about 7PSI.
If this pump fails, the problem is that often the truck will continue running, sometimes with no symptoms. The big issue with this is that the injection pump was not designed to “suck” fuel all the way from the fuel pump and as a result being forced to do so can result in IP problems down the road.
When symptoms do present themselves, they are typically a lack of power (fuel starvation) or difficult starts (Fuel draining back to the tank from IP and not being primed at key-on). Occasionally the engine will not start at all as is common with an already worn or sick injection pump which no longer has the strength to “suck” from the tank itself. Often, by the time these symptoms present themselves the damage to your IP may already have been done.
Diagnosis is fairly easy - when you turn the key on (without starting the engine) you should be able to hear the pump run for a second or three. Secondly (and more determining) by opening the water-drain tap (located on the engine near the alternator) you should be able to obtain a steady flow of fuel if opened and the ignition key cycled (You may want 2 people for this job...).
If you open this tap but do NOT get a strong flow of fuel with the key cycled to the “ON” position, your lift pump may not be functional. Although it’s technically safe to drive in this condition, it’s not wise....get it fixed - your IP will thank you and you will potentially save yourself the hassle and expense of an injection pump replacement down the road.
Again, If you need help, simply make a post here in the Diesel Place 6.5 forum, or search for previous posts on the subject using the “Search” function using the term “Lift Pump” specifically in the 6.5 forum.
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