I guess the title says it all. I've either a blown head gasket or have a cracked block in my 94 C-3500. The usual symptoms; steam in exhaust and exhaust gas bubbling in cooling system.

I'm planning today to use a laser temp sensor to measure exhaust gas temp at each exhaust manifold ports to try to identify which cylinders are involved. Any tips on further identifying the problem as cracked block or head gasket without first tear-down would sure help.

Also, I'm beginning the shopping for a replacement engine. First, I'd like to rule out those years prone to cracking.

I've read about blocks prone to cracking but all references are to casting numbers. Can someone condense that down to model years.

My impression is that the 94 and some 95 years were not prone to cracking at #8 cylinder and that some redesign of the block occured later and now in manufacture by other than GM. Any info to clarify will help.

Steve

All of them are prone to it, but more often than not it is a head gasket issue, I'd start there

Perhaps I should have said which are MOST prone to cracking.

Again is no definative most prone answer, my 98s members of the "oil spray" at risk engines are supposed to have failed by now, your 94 is one of the 599 "desired" blocks, which have had plenty of documented fails, all boils down to how they have been operated,

# 8 cylinder fails in themselves really aren't that common, most fails have been head gasket issues in rear, or main web fails, and crankshaft fails leading to the cylinder problems

Also a couple of us have been looking at way the block bores have been machined, several "Friday engines" may have had more meat removed from main web areas and putting a weakend area in play, combine with heat, may accelerate fails in some, and yet leave other not as succepatble to failing when not machined as much as some.

Since yours is a C series, it is easy for you to drain oil, drop pan, wipe mains down with laqquer thinner or acetone, walk away then come back in 15 min., and see if "spider veins" show up on the main webs, Diesel oil makes a great fault finder, works like FPI developer as it bleeds out of cracks.

BTW steamin how about updating your signature with truck information

Actually I have twice updated it but it seems not to be taking effect.

Steve

I guess it did this time. :o:

Steve

Got it now it looks like, thanks for being patient and making it work, lots of goofy happenings as they update the site,

For the rest of the guys if anything other than garage or classifed issues (we know those aren't up & running properly) are happening that don't allow you to post or search as you try to do, post what is or isn't working for you in the forum operations thread.

Ok we've measured the exhaust gas temp at the individual ports of the manifold on both sides. The front and rear on the passenger side (all that are accessible with the turbo still on) are lower temp by good measure than the driver side cylinders we can easily access. Number 8 cylinder is the lowest temp.

One engine builder out of North Carolina claiming 20 years of 6.2/6.5 build experience tells me they have never taken in a core that failed because of the head gasket. I read from Turbine Doc's last post that head gasket failure in the rear of the passenger side bank may very well happen.

What's your take on this?

I know that I can not rule out a circumferential crack in the number 8 cylinder without pulling the head to inspect. If cracked, another engine is the cure especially with 170K miles on the original engine. However I don't want to waste the money to pull the head if the head gasket really doesn't seem have potential to be the problem.

I've seen a statement that was supposedly from GM ,that the highest amount of #8 cracks incurred were in 1997/98 engines with the 5/8 engine oil cooler lines & piston oil spray. Supposedly the engines were in one ton(3500/3500HD in 1997 mdels. Hummers were mentioned also. Many changes are "running" in a given year,meaning not the full production year. That would give me the idea that 1998's could have more failures numerically,than1997.

Ok we've measured the exhaust gas temp at the individual ports of the manifold on both sides. The front and rear on the passenger side (all that are accessible with the turbo still on) are lower temp by good measure than the driver side cylinders we can easily access. Number 8 cylinder is the lowest temp.

One engine builder out of North Carolina claiming 20 years of 6.2/6.5 build experience tells me they have never taken in a core that failed because of the head gasket. I read from Turbine Doc's last post that head gasket failure in the rear of the passenger side bank may very well happen.

What's your take on this?

I know that I can not rule out a circumferential crack in the number 8 cylinder without pulling the head to inspect. If cracked, another engine is the cure especially with 170K miles on the original engine. However I don't want to waste the money to pull the head if the head gasket really doesn't seem have potential to be the problem.

If not going to pull the head to investigate what is the point just go ahead and take a guess that the block is bad and get a new engine, head gasket fail is a common ailment of the 6.5, I did not say the block would be cracked as result, but that due to commonality of generic head experince all 6.5s it is a possibility. If you are looking at a cracked block you will be replacing anyway I suppose, removing the head for inspection is free, I don't understand your logic that pulling head would be wasted money., it's bound to be less than a whole engine.

You will be pulling heads anyway if buying a short block, unless you are going to try & find a complete used but good; risky IMO because you don't know anything about the new/used engine, far better to pull down yours and investigate 170K is not really high miles for the 6.5

How many miles on the existing 1994 engine & what cooling up grades, if any? Is there a history of being overheated or any other trauma ? I can tell you this,I would only use machine shops referenced by this group or a well known dependable shop locally. IMO the problems by the advertising rebuilders remote to folks that are buying there are unaccetable to me. You are going to read that directly by those affected if they see your post & reply. If I had your problem & it was a block cylinder crack I would bore & sleeve just the affected cylinder , If all else were OK. My not knowing your ability or resources to solve this problem may nullify my solution.Good luck

For clarity, since I'm not doing the work as I can't get the vehicle into my shop and winter is coming on (I hate it even here in Alabama), pulling the head would not be a labor cost required for long block R&R which it the option I'm considering if the problem is not a head gasket.

What's your opinion on the "new" engines built on the General Engine Products (G.E.P.) block?



Steve

GEP is THE one to get, but it has to be a real GEP block, not a China clone, how are you going to determine head gasket is or is not an issue without pulling the head, am I missing something in translation. I speak fluent Alabama :D, I spend a LOT of time in Covington County my camp is just outside Andaluisa.

China clones require closce scrutiny, I'm using a China cast block in my rebuild the main line bore was just in limits, as were a couple of cylinders, I splayed my mains which took care of the crankshaft alignment, will be matching pistons/rings to each hole.

A "new longblock" with the China copy, the builder/vendor may or may not be as careful as you would be, and assume all specs are in tolerance, only way to know is check them. A real GEP block is only way you can have some confidence block is to spec out of the box, even then were it mine I'd want at a minimum the build sheet showing where builder had taken measurements

Pull the heads asap. I had a friend working on my truck and he waited too long too pull the heads. There was coolant in 2 cylinders and caused some problems. It would have been an easy put new heads on and be done. But caused pitting on the cylinder and also on the deck. GRRRRRRRRRRRRRRRRRRRRRR. Would have been an easy fix.

instead of pulling the heads can't u pull the glow plugs and c which one pukes green??? thats what i did.

So these arent as reliable as the 7.3's from ford?

For clarity, since I'm not doing the work as I can't get the vehicle into my shop and winter is coming on (I hate it even here in Alabama), pulling the head would not be a labor cost required for long block R&R which it the option I'm considering if the problem is not a head gasket.

What's your opinion on the "new" engines built on the General Engine Products (G.E.P.) block?



Steve

Maybe its early morning, but I wasn't aware of a Short-Block or a Long Block engine. What is the difference / Benefit of one or another? Or is it just more meat in-between cylinder walls &more webbing beef?

Short block= block /crank/pistons/ but no tin covers / NO heads
Long Block= complete engine with no tin covers (generally no valve covers or oil pan, also usually no IP or any other assorys)

and winter is coming on (I hate it even here in Alabama),
Steve
oh you poor thing,. you actually have to put on a sweater now and then??:D
nick

So these arent as reliable as the 7.3's from ford?

All I know is all the older 7.3s(Late 80s early 90s) the blocks had a casting defect and they sort of for lack of a better word rotted out and dumped coolant into the oil. Saw alot of them .Plenty of 6.9/7.3s also had headgasket problems. I had one. I'd say they are about even with known problems. Atleast that's what I experienced and I owned both.

The issue here is that if I have the head pulled and the block is cracked that labor money ($650) is wasted because it sure won't be applicable to the task of R&R ($850) to change the engine. And even if I do have it pulled I don't see how I can be certain that the block isn't cracked short of magnafluxing it which would require a total tear down.

I have some stinging memories of my first 6.2 head gasket adventure; $850 to the GMC shop for head gaskets including fluxing and pressure testing the heads only to fail again after 3 months or so. I replaced the engine with one from a salvage yard for $900 which I could have better spent the first $850 on.

My 6.5 in the 94 truck has 170,000 miles on it and logically it seems I would benefit greatly from a new engine; especially if I can get it in for less than $7,000. Let's not forget what a new truck costs and mine is still lookin good.

Steve

PS. An aside to Phantom 309. I was raised in South Dakota and spent 23 years in the Army with more than my fair share of time on the Czech border in Germany and on the DMZ in Korea so I know the cold. But that said, 30 deg F or less in Bama with the high humidity sucks real bad.

Sounds like you sort of have your mind made up, #1 I would not put in a used 6.5 to replace one with what may only have head gasket problem, you might be getting another problem. #2 if dropping in a rebuilt engine know your rebuilder and what parts they use, many on the net selling import stuff at low $$$ but, some not all; are low quality research before buying fully, buyer be ware.

I'm still puzzled why you are automatically deeming yours as a bad engine without all data to base the decision on. $650 to pull heads & inspect gasket seems kind of high who's doing the work independent or GM dealer, but is half of the bill to change gaskets, and unless going long block you are going to have to pull them anyway it is a lot cheaper in long run to freshen up your engine than replacement, if replacement isn't required.

Plus your suspicion is cracked nr 8 cylinder, we just don't see that as a event in itself often in the 6.5, usually that kind of issue is accompanied by some other mechanical problem, far more common is head gasket. If you are determined to replace the engine refer to nr 2 above

To me your math doesn't add up spend $650 for a maybe worst case if not worst case needing another 900 to fix, vs up to 7K for replacement in total, for a delta of $5500 ish, it is a gamble but IMO one worth making, or replace with new/new rebuild and tear it down yourself later and save for a spare or sell it

Ok here's the math.

1. Number 8 cylinder is running cold. This is verified and is likely the site of the failure. Is it cracked or not is the question. I read all over about the 6.5 block cracking in the #8 cylinder wall and producing exactly the symptoms I have. I just don't have confidence that we won't overlook a crack there by just doing a visual inspection thus wasting the money spent on head gaskets. If there was a way to be certain it was a head gasket failure I'd jump on that in a second.

2. I don't have a machine shop here I have any confidence in to rework the heads so short block is not an option. Thus, pulling the head and replacing the gaskets might fix it...but if not... that money is wasted as it is not applicable to long block change. But even if I shipped the heads to be redone I haven't found a source for a NEW short block with the new design block made in the USA and warranteed as the long block option.

3. I have confirmed that I can get a G.E.P. (AMF) manufactured engine for ~$6K shipped in to me. All new components. 3/36K warranty. If anyone knows of a short block in that configuration let me know please.

I've always thought my engine had a knock in the vicinity of the #8 cylinder that was stopped by venting the fuel from that injector but several diesel shops don't seem to hear what I do. Oil pressure is good on my engine as is power. But, we've blown a cooler line at highway speed and dumped all the oil. I caught it and shut down before damage but one never knows. My truck has had hard duty pulling a 21' Cape Horn back and forth from N. Bama to Florida to fish and before me a travel trailer all over the darned place by the previous owner. Maby I'm just paranoid but when one adds it all up it seems logical to me to change the engine.

What would you do given all this?

Pull the heads. Best case only gaskets. If you leave them with coolant in the cylinders only bad news. Could do a new set of heads. You can also do a new set of bearings with the motor in the truck. For about $1000 could be set up and run it til you need the other $5000 for a new engine. Mine had 145,000 on it and had next to no wear on the cylinders. Heads arent too hard to take off. Good bad or ugly would pull the heads so you don't ruin anything else.

By law all pricing has to be quoted to tear down & reassemble at a licensed shop. I suppose you could work a deal for tear down only, but if you were to need the old engine for a core, most rebuilders wont take a basket case for the core. If your buying brand new, that eliminates that problem. With that said, I agree with steamin & have been faced with this dilemma in my shop many times over the years. If you have the will & the means to replace it, just get it over with, could tear down at a later date & if it really only needs head gaskets, freshen it up & sell it. I am probably a fool, but a year ago, my 95 was getting bubbles in the coolant when i got to work in the morning, & it was pulled that night with a new gep on its way. I still dont regret it as the gep supposedly is far superior. My.02.

Here's an update.

We pulled both heads and found obvious head gasket failure with no apparent block cracks. Replaced the gaskets and had the heads worked. UNFORTUNATELY both heads were reported to be cracked on two cylinders and the shop doing the work went (without informing me) with the recommendation of the machine shop and had the heads repaired by some sleeving method I'm not aware of. I only learned this after the engine was reassembled. Cost for the machine work $675. I could have had new heads in house for $700. Ticked me off.

We also replace all glow plugs and injectors with remanufactured new nozzle injectors equal to OEM and installed a PCM relocation and heat sink device.

Now, when in neutral, the engine seems to want to "choke" with quite a bit of black smoke at around 2K rpm when "goosed". Quite different than it ran previously, as it was very quick to rev. Others who had driven it would always comment on how fast my engine would rev up compared the theirs.

The idle is satisfactory and the truck seems to run ok at speed. I wonder if the system has to do some sort of relearn to adjust to the change in fuel delivery from the new injectors. If that is the case, I wonder if there is some method to force the PCM into a relearn mode.

Also, engine oil pressure seems to be around 5 to 10 psi. less than it was. This seems strange since I can't think of anything we did that could affect oil pressure and it may be a coincidental sending unit issue so we plan to replace the sender today.

Any ideas or recommendations?

Steve

Before you replace that sending unit, put a direct pressure reading gage on it.

Here's an update.

We pulled both heads and found obvious head gasket failure with no apparent block cracks. Replaced the gaskets and had the heads worked. UNFORTUNATELY both heads were reported to be cracked on two cylinders and the shop doing the work went (without informing me) with the recommendation of the machine shop and had the heads repaired by some sleeving method I'm not aware of. I only learned this after the engine was reassembled. Cost for the machine work $675. I could have had new heads in house for $700. Ticked me off.

We also replace all glow plugs and injectors with remanufactured new nozzle injectors equal to OEM and installed a PCM relocation and heat sink device.

Now, when in neutral, the engine seems to want to "choke" with quite a bit of black smoke at around 2K rpm when "goosed". Quite different than it ran previously, as it was very quick to rev. Others who had driven it would always comment on how fast my engine would rev up compared the theirs.

The idle is satisfactory and the truck seems to run ok at speed. I wonder if the system has to do some sort of relearn to adjust to the change in fuel delivery from the new injectors. If that is the case, I wonder if there is some method to force the PCM into a relearn mode.

Also, engine oil pressure seems to be around 5 to 10 psi. less than it was. This seems strange since I can't think of anything we did that could affect oil pressure and it may be a coincidental sending unit issue so we plan to replace the sender today.

Any ideas or recommendations?

Steve

Hopefully they sleeved all, as was explained to me by the machine shop I deal with, they have never had one leak after it was done, besides your "New" heads would just crack again edventually, this way you should never see them crack (between the valves). as for the black smoke check to see that all the hoses to/from the wastegate are not broken & are hooked up

I have fixed the knock. It was the aluminum coolant bypass pipe touching an injector line. I must surmise that the noise was being transferred by the coolant in the hose to the heater core and being amplified there. Hence I could hear it loud in the cab but no noise in the engine compartment.

Now to deal with the low oil pressure.

I've changed the sending unit...I didn't trust it anyway. The oil pressure when warm is running 2 marks below 40 at speed and 1 to 2 marks above the FIRST red mark (the one above zero) at idle.

The oil seemed a little thin and smelled burnt with only 100 miles on it so I changed it today with 15/40 Rotella. No change to the pressure.

My concern is that some debris may have either clogged the pick-up screen or may have blocked drain passages back to the pan thus starving the oil pick-up by the pump when at speed. I'm leaning to pulling the pan and changing the pump to a 97 or later model for increase in volume and pressure or at minimum replacing mine with OEM. Might (if I aint to skeert) pull the main bearing caps and inspect/change the bearings too while the pan is off. ANYONE DONE THAT?

The smoking is present when "goosing" it in neutral. Very little smoke at speed when accelerating hard. I'm pleased with that.

Well the oil pressure remains low. Measured with mechanical gauge to be 5 psi warm idle and 25 psi warm at 2K rpm.

We are changing the oil pump to a 97 model pump and inspecting/changing main bearings and rod bearings as required.

I'll let ya know the outcome.

Steve

i,m a little confused here,. whats the difference between oil pumps? i,ve never noticed any difference.?? the lower oil pressure might be a direct result of glycol in the oil and worn off some babit material off the bearings,.as for your black smoke,. i,d be looking at pump timing for that problem,..
jmho,.
nick

Smoke when goosing the throttle in neutral is normal as the turbo has not yet built boost for the amount of fuel that you dumped when "goosing".
IIRC 1psi per 1000rpm as a general rule of thumb is OK

i,m a little confused here,. whats the difference between oil pumps? i,ve never noticed any difference.?? the lower oil pressure might be a direct result of glycol in the oil and worn off some babit material off the bearings,.as for your black smoke,. i,d be looking at pump timing for that problem,..
jmho,.
nick
The 1997 oil pump will have a higher volume due to the later piston oiler blocks that need the extra oil. It sounds like his main bearings are worn.

Well the oil pressure remains low. Measured with mechanical gauge to be 5 psi warm idle and 25 psi warm at 2K rpm.

We are changing the oil pump to a 97 model pump and inspecting/changing main bearings and rod bearings as required.

I'll let ya know the outcome.

Steve Sounds like you have worn bearings. :(If you use the 97 Melling Oil Pump, be advised that the pick-up tube screen will sit about 3/4 inch lower in the oil pan than the stock pump.

IIRC 1psi per 1000rpm as a general rule of thumb is OK

10 PSI per 1000 rpm is what i have always used

10 PSI per 1000 rpm is what i have always used

10 per 1,000?!?! :eek: You mean to tell me at WOT this block is seeing 30 psi?

10 per 1,000?!?! :eek: You mean to tell me at WOT this block is seeing 30 psi?

I'll see if I can find it in some old tech manuals I have, ( memory is bad maybe it was 1psi per 100, or 10 per 1000) all it means is that the engine would still hold together and run at lower psi than you would expect. your motor likely makes more than 30psi at WOT, but probably does not need to. lower than stock psi indicates worn parts ie, oil pump/cam/crank/rod bearings, I've also seen some engines knocking like mad and the oil light still would/did not come on, low oil pressure in its self does not cause the parts to wear. most wear caused on start up with NO oil pressure, and excessive engine load causing the oil between the crank and rod bearings to be forced out, allowing metal to metal contact.(dino oil holds 500psi before shearing away, pretty good huh, any syn oil its 3000psi,)
I was looking thru a parts book a couple months ago, looking for oil pressure senders to use on my dodge fuel system (wanted to wire in a low pressure warning light) and there were lots that would trip the warning light in the 3-5psi range

10 per 1,000?!?! :eek: You mean to tell me at WOT this block is seeing 30 psi?


We are talking about oil pressure....

Hopefully they sleeved all, as was explained to me by the machine shop I deal with, they have never had one leak after it was done, besides your "New" heads would just crack again edventually, this way you should never see them crack (between the valves). as for the black smoke check to see that all the hoses to/from the wastegate are not broken & are hooked up

What exactly is sleeving in relation to heads?

Whenever we had cracked heads we pitched them.

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