I swore I would never do this, but with the price of gasoline, I am looking at replacing at least one of my work trucks with a 6.5 Diesel 2500 or 3500 chassis.

Which model years are the best and why? What modifications should be considered mandatory for the truck to be as reliable as a gas 5.7 or 7.4?

No electronics 92/93. Best of theOBD 2 is 99/2000 & with the final cooling system upgrades.Needs PMD/FSD relocated. you're the one that needs to be reliable. Reliable to do all the upgrade improvements to start with,buy the books & educate yourself with product knowledge. Obvously you're interested in fuel cost so a manual trans will give the best MPG & available power to the wheels. If you can make do with single rear wheel capacity, another bonus to the MPG. A 7200 GVW 2500 Manual trans can weigh 5100 lbs & a 3500 4 wd dually crewcab weighs over 7500 lb against a 10000GVW than. Truck in sig weighs 5400 lb has 3200lb cargo capacity @ GVW,gets 20 to 23 mpg,no cargo, in highly congested south orange county ,Ca freeway ,slowing & going driving.Former owner claimed 27 MPG,empty solo cross counry.A SRW 3500 would have 400 more GVW & gain a few pounds of curb weight . So a 2500 for all practical purposes is just as good ,same brakes. I believe my 2500 could use a 3.08 diff non towing for an improvement in MPG with an accurate driver.I also think it would do fine towing ,using 4th gear with a 3.08. Want to buy it? Ha Ha. Use due diligence on any truck you look at. Combustion in cooling system, blow by,crankcase vent normal,etc.Cracks in block & heads are the 6.5 bane . These trucks have low market value vs the Ford & Dodge but have multiple achilles heels for you to guard. Good luck

On top of what 4door said, the FAQ's section has a lot of great info on all of the mods that should be done for reliability, cooling, and performance. Even a part on what to look for when buying a used truck. If you're looking for anything in particular the search feature works good as well.

First I'm going to say that I am no diesel guru even though I own one, and then I am going to question your basic assumption that these diesels are not as reliable as the gas engines. Just because you see a lot of problems talked about on sites like this doesn't mean that there aren't hundreds of thousands of these engines out there that have no problems at all.

Although I am sure I am going to get yelled at here, I also question that many of these "improvements" increase reliability. Lot's of folks here like to tweak engine, exhaust, turbo, cooling, etc., thinking those tweaks make them better (some may, I'm not saying "never"). That's fine if that is what you want to do, but overall reliability will suffer. Lots of people advise that you have to do the cooling upgrade, but if you don't tow 10,000 lbs and your engine never overheats, why do that? Same with the PMD relocation. A good example are some aftermarket air filter systems that I know from an engineering point of view have to decrease performance and increase heat load on the engine, but people still add them for "more power".

I'm not saying anything about the specific recommendations made here by others - these things may have been necessary for them. But we also don't know enough about your application to say "you need to do this" either...IMHO.

There is an old saying that has a lot of value in my opinion: If it ain't broke, don't fix it.

Ditto instarx. I have a 1994 C2500 6.5 NA, Manual trans. that is still pretty mutch stock as it left the factory with the addition of 213,000 miles. I replaced the clutch last year. I am going to replace the injectors tonight only because of mileage and I will replaced the IP tonight as well, due to a fuel solenoid that is taking to long to seat. The PMD is still mounted to it and it has run just fine for a long time. Everything else is still the way it came out of the factory. Ooops, well not quite. The A/C compressor was changed sometime back.

Dan

Only one I got to disagree with you guys on is PMD, it is broke in present location & needs fixing, too many documented cases that say otherwise, GM could not admit it was broke and do a campaign to fix it wholesale, too much liability, plus cheaper to fix by attrition via extended warranty, also if during diagnostic phase we can trump up some "faults" that can be blamed on the owner, those will soften the blow. GM knew there were design problems from get go, & had to issue a "special policy" rather than have the issue show in light of day in a courthouse, can we say liability if acknowledged, ever had a PMD die on you while in traffic with a load on, it ain't pretty folks trust me, angels from above & God's watchful eye are only reason I'm here to tell the tale.

Okay 2 to disagree on, cooling also broken, if not why did GM redesign the cooling system, because as original designed wasn't doing well at cooling engine as originally designed.

Now 3 boost fooling IMO is an upgrade that will actually increase life if not gone too far, to a point more boost actually lowers engine operating temps overall, GM did not spend the $$$ to include Boost & EGT monitoring in it's programs, IMO costing them huge amounts of $$$ warranty. Instead they chose to use an algorythm to de fuel or de-boost if certain parameters went out of range, tier 1 defense on stock truck is be-boost- 2nd tier of defense is defuel.

All good if truck is healthy and boost system is working, & has a broken boost system and no ability to de-boost, already running de-boosted. Then comes Joe Average that does not know anything except that his truck won't go as fast as it once did, he just puts more throttle to it making it try to run faster, worsening conditions, in limp mode there is a 50 mm max fuel rate, but Joe Average will keep that 50 mm firewall requested until engine quits.

Remember fuel without boost is max EGT situation something over time is going to have to go, so making boost more available (within limits) is a good thing GM design team did some good ground work, but every design can be improved upon, does your truck need to be capable of pulling 18K no it doesen't, 99% of the time I don't pull that way either.

I haven't hit my ROI point for mods yet, but since it would cost me about $500 each way to move my tractor or backhoe to my camp & back to a safe location where I store them it won't be much longer until I meet my break point.

If it ain't broke don't fix it is a good rule, but in there are several things on the 6.5 system while not really broke, are marginally designed, handshakers without added heat of a transmission seem to do better over the long haul,.

Lions share of what goes bad with the 6.5 all comes back to heat balance of the system, heads warp insufficient cooling/gaskets blow, PMDs die electronic componnents in too hot of an environment, engine dies some postulate inequity in cooling & expansion rates bring out worst in casting or other problems with block, if GM had done just a little more homework they could have gotten a better machine. Now what you see as fixes on boards comes from 20+ years of 6.2 & 6.5 common experience best for us with boards we can share experiences , & a huge data base of experiences for what works & what don't. Gm did not have the luxury of time & data collection like we do, plus have to decide whether an extra $500 spent over potential sales projections gets them a fast ROI.

So GM mostly got it rite, for a LD engine growth of the 6.2 designed in 70's to market in 80s, to 6.5 design in late 80's first to market in 93, updated to EFI in 94, to OBD-II in 96, to H/O cooling in 97, & best of all years 99-00. see the 6.5 was changed by GM & was steps in right direction, they stopped with introduction of DMAX whole different machine.

I suspect if GM was going to stay with production of the 6.5 many of the aftermarket fixes we as a community & vendors that looked into 6.5 ailments early on found worked, would have eventually been part of the stock offering of the 6.5.


1995 G30 1-ton van, 6.5L non-turbo[/ what is this??? it ain't a real truck :D :D , joking aside a non turbo has whole different heat balance profile as does 5 spd trans as mentioned earlier, which IMO even if we agree to disagree is root of all evil when it comes to the 6.5 system, it may not be broke , could stand to see some improvement, glad yours is holding up well for you.

...Although I am sure I am going to get yelled at here, I also question that many of these "improvements" increase reliability. Lot's of folks here like to tweak engine, exhaust, turbo, cooling, etc., thinking those tweaks make them better (some may, I'm not saying "never"). That's fine if that is what you want to do, but overall reliability will suffer. ..


No yelling here. I just believe that the nature of your assertion is not entirely correct. My belief, subtianted by "real world" experience, is that the following items WILL increase reliability of an electronic 6.5TD equipped vehicle: Remote PMD cooler (preferably located out of the engine bay), turbomaster (how many vacuum pump and W/G solenoid problems have you read about here?), and OPS relay installation (takes the electrical load off of the OPS switch and transfers it to a load-rated relay).

To the contrary, the following items are performance enhancements that are often "justified" as reliability improvements (by the purchaser or retailer) but are actually performance-based modifications: Removal of soot trap (aka "kitty" or "catalytic converter"), bigger exhaust, performance chip or reflash, boost fooler mod, and '97+ cooling mods. There are likely more that I can't recall at the moment, but these seem to be the big hitters.

There is an old saying that has a lot of value in my opinion: If it ain't broke, don't fix it.

The problem with applying this statement to a 6.5TD, is that by the time you realize that it may be broken it has already "bitten" you! One "enhancement" that I ALWAYS recommend though, is gauges. For a 6.5TD, you should always have at least a boost gauge and a pyrometer to monitor the life-giving turbo performance and the potentially life-ending exhaust gas temperature. The "justification" for always recommending these is that over time you will learn to use these gauges to judge the health and well-being of your 6.5TD...

Regards,

1995 G30 1-ton van, 6.5L non-turbo[/ what is this??? it ain't a real truck :D :D , joking aside a non turbo has whole different heat balance profile as does 5 spd trans as mentioned earlier, which IMO even if we agree to disagree is root of all evil when it comes to the 6.5 system, it may not be broke , could stand to see some improvement, glad yours is holding up well for you.

Ha, ha, everybody's a comodian. :) Well, it actually IS a truck, just doesn't have an open bed. Let's see the typical pick-up haul a ton of sugar or electronic equipment in a driving rainstorm and get it there dry - mine could. But no offense taken. Please note that I was careful not to hold my truck up as an example of "leave it alone" success - because it is not typical.:)

As for GM making some changes such as cooling upgrade, I suspect that was made to improve cooling in the extreme 3-5% of hard use cases. That mod is probably not needed in the vast majority of 6.5Ls.

I'm not saying that these mods are never needed, just that there are hundreds of thousands of these engines out there that have never had them and they are running fine. I think that's hard to argue with.

Every vehicle needs to be evaluated individually, but I think it is a mistake to just automatically assume that they all need these upgrades to be reliable.

BH1, as a newer member of this community I can tell you that there is a wealth of knowledge on this site. I can also tell you that the FAQ and search on this site will bring up almost anything you want to know about the 6.5 engine and if it doesn't, the members here will help you troubleshoot your problem if you have one. My 94 has 215k on it and was all stock. With that amount of mileage I agree with the term "if it ain't broke don't fix it" but only to a certain point. I decided to do some of the mods that were discussed in previous posts and I can tell you that they make a big difference in the overall performance of the engine. IMHO the mods that you can do to the 6.5 are pretty cheap compared to other vehicles out there, you can't beat the warranties that are offered on them and they increase the overall performance and longevity of the engine.

If you are looking to buy a 6.5 , I think you will be happy with all aspects of it. There is a section in the FAQ's about what to consider when purchasing and a lot of other info there too. Hope this helps.

http://www.dieselplace.com/forum/showthread.php?t=53309

I would rather have a 2001-2002 Duramax truck, but I'm not going to spend that kind of money for a work truck.

I am a 88-98 CK fanatic... I own 6... A 96 K1500 Suburban, a 96 C3500 Dually, an 89 C2500 a 96 K1500 Z-71, a 93 Blazer, and a 94 C1500. They are all dead stock, right down to the AC Delco batteries.

I own an Auto and Truck Repair Business, and we get to work on the 6.5's from time to time. We had a 99 K2500 with the 6.5 in the shop the other day for a starter replacement, and during the test drive I was pretty impressed with the acceleration it had for a stock truck. Seems like it ran a lot better than the older (Pre 97 trucks) I've had in the shop.

The only reason I am looking into a Diesel truck is to burn Bio Diesel. I'm looking at buying my own outfit to make Bio Diesel. I have a small Trucking and Excavation business, and it would be nice to make my own fuel for my skid loaders and tractors. My home has a fuel oil furnace, so I could save a considerable amount of money in a year's time.

The only reason I am looking into a Diesel truck is to burn Bio Diesel. I'm looking at buying my own outfit to make Bio Diesel. I have a small Trucking and Excavation business, and it would be nice to make my own fuel for my skid loaders and tractors. My home has a fuel oil furnace, so I could save a considerable amount of money in a year's time.
good luck - I think you'll like it. There are quite a few bio users here, so don't forget to visit the FLUIDS section.

The only reason I am looking into a Diesel truck is to burn Bio Diesel. I'm looking at buying my own outfit to make Bio Diesel. I have a small Trucking and Excavation business, and it would be nice to make my own fuel for my skid loaders and tractors. My home has a fuel oil furnace, so I could save a considerable amount of money in a year's time.

BH1,

Welcome to the crew. During the last 4 years, I've run lots of biodiesel in my '93, including some home brew and some commercial B100. The most important mod I've made for bio is the Oil Pressure Switch (OPS) relay setup. A heavy duty lift pump & secondary filter make a difference, as well. For a couple of years, I kept getting stalls on warm restarts, replacing lift pumps and tearing my hair out. The higher viscosity of biodiesel seemed to push the already weak OPS over its limits regularly, especially in cool or cold weather. Read the 6.5 FAQs for in-depth info on the fuel system. Since I did the OPS / lift pump / aux. filter upgrades in early 2006, my truck has been rock solid, no stalling. I tow some times; the strong fuel system makes a difference IMO.

As a couple of the guys said earlier, the best 6.5s seem to be early or late models: '92-93 or '99-2000.

I would rather have a 2001-2002 Duramax truck, but I'm not going to spend that kind of money for a work truck.

. Us neither those of us that reside in Jurassic Park here home to the Diesel dinosaurs by comparison to the DMAX et als, now that we have like minded souls to commisurate with love the maintainability of 6.5 & relatively low cost of repair parts, for what a couple of injectors on the 6.6 cost 6.5 can have a whole set. As the 6.5s go by way of the scap pile, I'll eventually go DMAX, but as long as my ole 6.5's are able to make their way I'll keep on plugging away with them.

Today I made my virgin long haul trip with my last year acquired 6.5 Burb, 21mpg for a full size SUV ain't too shabby 500 miles avg 70-75 mph MS to FL 2000rpm, reflash, TM, 4" exhaust she will easily scoot to 100mph with a decent acceleration ability. Rather pleased with way it ran over here to FL

Thanks to all of you who have posted a reply.

I'm going to keep my eye out for a nice 6.5 truck and see what turns up. As for Bio Diesel, I would much rather pay the money for a Bio Mixing Station, than keep paying the oil companies for their overpriced Gasoline and Diesel Fuel. I'm about sick to death of having to fight my way through a line of lottery ticket scratch off buyers just to pre pay for my fuel, and then have to get a refund when I can't put as much fuel in the truck as I paid for.

BH...I've had enough. My time is too valuable to waste and I'm tired of giving up my profits for fuel expenses.