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Hey everyone, I have owned a 98 suburban with a 6.5 diesel and 246,000 miles since May. I have done quite a few upgrades and fixes including replacing the hydro boost, new braided oil lines, relocated pmd, new glow plugs. I also upgraded to the larger fan clutch and fan. I also rebuilt the whole front end. I was looking under the truck today, and noticed that there was some coolant seeping. I looked up under the driver’s side, and can clearly see where the coolant is leaking externally between the head and the block on the back corner. I know I am in for a head gasket job, but wanted to come here for some collective advice. Is this engine worth doing a head gasket on, or too many miles on it? Are there any common issues I need to know about such as heads prone to cracking or block issues with this year? The truck has not over heated in my time owning it, and the only time the temp climbs a little is when towing a car trailer up long grades (never exceeds 210). Is there a good how to guide out there for doing the head gaskets on this engine?
 

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I would check blow-by to get a good idea of engine health, before deciding. If you have excessive blow-by or pulsing blow-by, you might want to consider replacing the engine with a military take out (Navistar block). If you have little blow-by then it might be worth doing the head gasket job.
I would check your upper radiator hose for building pressure when cold-started. If it does build pressure then you also have combustion gases getting into cooling system via bad head gasket.

Keep in mind, I am not a mechanic. Just thought I would share this two cents.
 

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I did the oil cap blow-by check before I bought it. I saw virtually no smoke but will check it again today. The upper rad hose also does not get hard while the engine is warming up or on a cold engine. No smoke out the pipe unless I floor it on acceleration and get some black smoke (only done once or twice). Starts easily. seems to run great other than I hear an injector noise from the turbo side (was able to isolate a clicking noise to an injector using a screwdriver as a stethoscope).

We've got a baby on the way in March and a lot of other expenses related to that, so I am trying to figure out the most economical way to handle this (but reliability is important to me). I also can't have the vehicle down for too long. If the heads look okay when I pull them, what should I do? I am tentatively thinking...fix the head gasket leak, but then save up to get a lower mileage engine long term. I don't know if the 6.2 is compatible, but I think I can get a low mileage used 6.2 from tedstrucks for cheaper than I could rebuild my current 6.5 for if that were needed. From everything I am reading online it seems like my mileage is getting towards the end of the useful life of most 6.5 diesels. If everything is relatively good...would I benefit from taking the extra time and re-ringing and replacing bearings in the bottom end, or would that be stupid without tearing everything down and sending it to a machine shop? Again, it runs fine, but I would be reasonably annoyed if in a year I throw a rod or spin a bearing.

I am thinking...pull heads, if they are not cracked...check for flatness and reuse them. I know I will need head gaskets, a head gasket set, intake manifold gaskets. I should probably also replace the injectors due to the aforementioned noise and not knowing how long they have been on. I did find this set of heads near where my wife's parents live: https://baltimore.craigslist.org/pts/d/gambrills-cylinder-heads-gmc-diesel/6741974051.html

I have done plenty of head gasket jobs before but have always had a spare vehicle and could take my time...I don't quite have that luxury right now.

Anything else I should be thinking of? Do I need to worry about valve stem seals, etc? I don't have the tools to change them (and have never done that before) but am sure I can figure it out. Where I currently live we don't have any very good machine shops so most shops send out their heads/blocks for work elsewhere. Is there anything else I should look for on the block?

Also, I get the P0251 and p1216 codes about once every 3-4 months. I am guessing that means the IP may be on it's way out soon? If so, would something like this be a good buy and just replace the optical sensor or too risky: https://baltimore.craigslist.org/pts/d/jarrettsville-gm-65-turbo-diesel-parts/6759025852.html ?

Thanks for the advice guys...this forum is great! I love the diesel suburban, and enjoy driving it so much more than the old 5.7 vortec yukon I had or the 5.7 tbi suburban I used to have. Gas mileage is better and so much more low end torque when pulling my double axle car trailer.
 

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Not sure if this is good advice but with the mileage you have I would just try Bars leak to "fix" the leak. Then look for a replacement. Think when you tear it apart it's going to show stuff you don't want to see.

Way I have done bars leak and have had excellent results, is to remove a bit of water from radiator so you can pour all the stuff in. Top it off with water and go drive it till it gets to temp. Park the vehicle overnite. Minor leaks will seal up quite nicely.

If it was water in oil, or blowing water out radiator I would not use it.
 

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The 6.2L conversion would need some extra work. DB2 IP, trans controller, engine harness, etc..

If I considered using the craigslist heads I would have them tested beforehand
I would first pull your heads and inspect/test the heads. Inspect the surface areas of the block for pitting and go from there.

Here is the DTC and diagnostic procedures manual in .pdf format for your computer to aid in diagnostic of those codes:
https://www.dieselplace.com/forum/attachments/63-gm-diesel-engines/21-6-5l-diesel-engine/342194d1429922509-gm-6-5-faq-obd-codes-diy-parts-list-manuals-info-sticky-look-here-first-1998-6.5l-obdii-dtc-diagnostics-procedures.pdf

The P0251 code info starts on page #98
 

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Hey everyone, I have owned a 98 suburban with a 6.5 diesel and 246,000 miles since May. I have done quite a few upgrades and fixes including replacing the hydro boost, new braided oil lines, relocated pmd, new glow plugs. I also upgraded to the larger fan clutch and fan. I also rebuilt the whole front end. I was looking under the truck today, and noticed that there was some coolant seeping. I looked up under the driver’s side, and can clearly see where the coolant is leaking externally between the head and the block on the back corner. I know I am in for a head gasket job, but wanted to come here for some collective advice. Is this engine worth doing a head gasket on, or too many miles on it? Are there any common issues I need to know about such as heads prone to cracking or block issues with this year? The truck has not over heated in my time owning it, and the only time the temp climbs a little is when towing a car trailer up long grades (never exceeds 210). Is there a good how to guide out there for doing the head gaskets on this engine?
Are you sure it’s not the top plate leaking under the glow plug controller?They sometimes do leak there.Also a 6.2 engine would work.Just remember to install the crankshaft sprocket with reluctor built in for the crankshaft signal.You’d also need to use your own front timing cover since it has the crankshaft sensor in position.
 

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At the price of an oem head gasket set... say from napa (cheap) the head tty bolts aren't that bad either. Not like buying a stud set.

I'd pull both the heads, inspect the bores, throw it back together. The longer it sits as it is (if you do have a blown hg) the more likely the bores will get rusty and bad.

Throw it back together THEN do a comp test and check blow by.

If you don't have arp studs then it should take a day (as long as you stay on it)

Just my 2cents. :thumb:
 

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If you want a reliable million km engine, I'd get a new 4BT with stock fuel and hp setup.


But if you're also broke as me I'd most likely replace the headgaskets on both sides, replace/fix the injectors, look if the heads are ok(check the nylon rocker arms if broken) and lap the valves. You can rent a tool that looks like an oversized C clamp to release the valve springs from most autoshops.
 

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Discussion Starter #10
One of you mentioned a plate near the glow plug controller...having a hard time seeing a plate but I do see some coolant in the intake valley as well. First two pictures are near the glow plug controller and FFM. Bottom picture is looking at back corner of driver’s side head. There is dexcool both in the lifter valley and in this back corner. Is there something else I should check first? To me it looks like it is dripping right between the head and the block up top and underneath, but I might be missing something. There is also some unrelated p/s fluid residue from my old brake booster underneath so don’t let that throw you.
 

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The plate is under the glow plug controller.When the controller is out of the way along with a bracket on some models you’ll see the plate.
 

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Here’s the location....
 

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Could also be leaking up front under the coolant crossover as well sending coolant down in the valley of the engine.
 

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Discussion Starter #14
Thanks for the extra information...I’ll take a close look in the morning at that plate. Also, when talking about the coolant crossover are you referring to something near the thermostat housing?
 

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I checked the back side of that plate with a mirror...looks dry there. It is hard to see all of the crossover pipe that the thermostat housing is attached to and I couldn’t find any visible leaks. I did notice as the engine was cooling down from having to drive it earlier that there was wetness where the driver’s side head meets the block on the top...and a dripping from the same corner I posted a photo of before on the bottom. I am thinking it is pretty much a sure bet of the head gasket at this point. Still no signs of oil/coolant exchange. The engine did have an odd faint ticking that seems new to me, but it could be from combustion gasses escaping possibly. I’m going to try my best to locate some heads, but the more I am reading on this topic there seems like a good chance that there may be block issues to. Hoping I can band aid things together for now and then save up for an engine (sounds like these blocks usually aren’t rebuildable)
 

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Discussion Starter #18
Used the pressure tester and it is definitely coming out from the head gasket in the back corner. A little concerned since it is near the infamous #8 cylinder but I won't really know anything until I pull the heads. I am still thinking of picking up some used heads...including some pictures from some local to me that the guy sent me. Are these the right heads for a 6.5 TD suburban? Not completely sure how to tell the difference between the 60 and 90 degree heads, or the 6.2 heads? I figure if I pull the heads and the block has a problem, I can just re-sell them but I would rather have some on hand. Other than that, what do I need to be looking for in the block. I have read about a common cracking point near cylinder eight?
 

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From what I can see, those will work, when you see them in person look dor a "diamond" or "T" stamped on the precups... and the intake bolt holes should be a 90* from the gasket surface.



Chances are only a blown gasket, if a cly was cracked you would have water in the oil or cylinder.
 

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The usual spot for these heads to crack is the wall between the exhaust and inlet valves.
Some early 6.2 heads can't be used for 6.5 becouse of some injector interference problems.
I'd reccommend using your current heads and new ARP head studs(don't use original studs over again, they will break if you torque them), but if you feel safer having another pair of heads go for it.
 
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