View Full Version : Another crank failure theory .... oil temperature
Ok I was talking to my cousin who mechanics a lot over the holidays. He works for a municiple garage and sees a lot of engines. Recently 5 broke 6.5 cranks over a couple of weeks/months. He said oil temp may be an issue and the bearing and journals are getting too hot. I asked him what he thought about the harmonic balancer failures and he did not comment on the appearance of HB on these particular failures but he mentioned Fluidamper and importance of a good HB. He mentioned oil passage size at the front cam bearing changed but I missed the specifics, as I pointed out the oil spray coolers and increased oil flow for 97+ engines.
It has always struck me that the 6.5 has so little oil capacity compared to the other pickup diesels. But have read many times cylinders have very little wear with many miles on the engine so I let it go and figure oil is probably adequate.
I use to think oil should get to 212F then a few threads a long time ago and several hours of reading changed my mind. A new thread started me thinking again and I wonder just how hot does oil and bearing surfaces get in the engine? I have read too much to find it all again but thought I saw a blurb about cam journal bearing getting really hot (can't find it again but 300-400F I think). And of course the piston face is seeing really hot temps up to 3000F combustion temps and EGT of up to 900-1000F are measured towing. Blowby will be related to EGT and I never really thought about just how hot the upper ring and oil is getting. But apparently it lives ok.
Back to the crank and main bearings. After reading I am now curious just how hot do you think the crank and journals are getting locally? I've never heard anyone say the crank was blued or changed color due to heat but after failure its hard to determine the last few moments and chain of events. I also haven't read of many spun bearings but maybe its not getting hot enough to gual but still hot enough to encourage failure???? I have read the turbo will choke or oil will coke if shut down hot. I am guessing mains and cam bearings are not that hot and/or can dissipate the heat better. I imagine the continuous flow keeps the oil from cooking but I am starting to think it momentarily gets really hot at some points in the engine.
Just food for thought.
IF I was guessing and I am a bit here.
I don't think for a minute the broken cranks referred to were caused by oil temp.
Piston and bearing failure should occur first before any crank breakage.
I would stick with a known problem on the 6.5 and that is the balancers.
Harmonics can break things but heat usually would take out the bearing first and by time things got to beating the crap outa everything the driver should hear it and shut it down before a crank would break.
My guess is that the cranks all broke at about the same journal indicative of the balancer failure.
There again I could be all wet but its what makes sense to me.
Merle
Howdy.
The theories about crank breakage in the 6.2 and 6.5 has and will go on for a long time yet unless someone takes it upon themselves to do some very in depth studies and sme serious computer anaylisis.
The oil temp and such is not normally an issues in these engines unless someone is just plain abusive to the engine and is not keeping good oil in the sump as well as keeping the level correct.
I personally have seen these engines apart with anywhere from 100K to as much as 300+K miles on the original factory parts.
The bearings and the journals generally look great with only normal wear on the babitt insert materials.
The bearings are very much like a barometer of engine health.
The insert bearings are made of various materials all layered together to form the bearing surface.
Generally the high mile engines will show the rods well worn down into the under layers of the bearings but still functional.
With the exception of a couple engines that either were run out of oil or had broken something I have not seen a crank with journals that were not suitable to accept new bearings and go right back to work even with very high miles.
My Burb as an example 237K on the clock and all I did was spin the crank and pollish the journals lightly with crocus cloth.
I used standard bearings instead of the select fit. The clearances were a little wierd and the spread between journals was a little bit all over the map but still within specs, so, screw it, back together with it.
The engine now has about 30K on it since the build and runs sweet and the oil pressure is really great.
This engine was/is a 599 block with large bolts in the mains at both locations.
The Cam was perfect all the way with not so much as a scratch on any lobes. The cam bearings in this engine were the copper colored ones and not a babitt type bearing. These bearings showed hardly any wear and the factory ones are still there doing the job.
The 6.5 is a top oiler, meaning that the cam gets oil first and then from there the oil is fed to the crank instead of like some other V8's that feed the crank first.
The top ends was likewise great with no visible wear of consequence on any of the rockers/shafts
The pistons were all in good shape with no scuffing and abnormal wear showing.
The cylinder walls showed almost no wear and the crosshatch honing marks were still visible in all the cylinders even in the ring travel.
The low cylinder wear can be contributed to the fact that this is an oil burning engine and the cylinders dont get flushed of lubrication at times like a gas engine can.
The original rings actually looked great but to reinstall would be foolish.
I have not seen any indications of over temp on the oil as much of an issue.
Let just say for instance that oiling was a contributing factor, now what would we be seeing??? the first thing that would probably show up would be extreame bearing wear and or failure.
The exact opposite has been the case.
Even in engines that have snapped a crank many times the bearings are still intact even on the broken journal (If its shut off quickly after it starts making noise)
The issue of the broken cranks are begining to (AS has been pointed out by some other of our knowledgable members) look like a serious harmonic issue due to the opperating dynamics of these engines.
The example has been made that the trucks with lower gears, which results in the engines opperating at the upper end of the rated RPM band seldom see crank and block failure.
The most troublesome issue may very well be the terrific harmonic beating that these little critters are taking.
The need for a superb Vibration dampener has been almost proven beyond reproach.
The lower RPM areas in the engines can and does produce some nasty
harmonics and this stuff is just like flexing the old hairpin back and forth and sooner or later it breaks.
I personally dont think lube oil and bearing temps is any real issue here as far as the block and crank breakage.
Just no real evidence of that scenario showing up.
There certainly is the possibility and likelyhood that some engines have failed due to low oil and the resultant lack of lube but this would /will result in failed bearings and the reasons would be very obvious.
The normal engine oil temp in these engines is well within reasonable limits.
250F is tollerable for most engine oils for a while anyway.
In the class 8 stuff I see my engine oil temp right about the same as the coolant temp or slightly cooler depending on the ambient. Rarely do I see this above the coolant temp except maybe on a very hot day and then only for a short time right before the auto controls turn the fan on.
If the parts such as the crank and cam were getting excessively hot to the point of breaking down the oil (cooking it) the evidence would be right there to see, as coking or dark burned areas of oil staining on the journals and bearings.
This is just not seen.
The turbo has the most hellish life on these engines and even these little creatures can live well into the 200K+ arena.
My 94 has the original Turbo and now has 257K on the clock.
I did pull it all apart and clean the little thing up good.
I removed the turbine and the compressor wheels and completely cleaned the thing inside and out.]
The shaft looked perfect as did the seal rings, housings and rotating parts. Even the bronze bearing was perfect.
The turbo can and will run a loooooooooooooooooooong time if the oil is kept clean and free flowing.
A few things kill turbo's quickly. Junk flying through the turbine, junk allowed into the compressor. Shutting down the engine too quickly after a hard hot run.
Allow the turbo to cool for a little bit so there is less heat and the residual oil does not "Coke UP" or burn in the turbo bearing.
A good thread and this discussion will probably get much more attention before its over.
Just a side note here
I bought a complet 1994 6.2 (yes they did make some) I bought the engine for the Banks setup that was on it.
The fool had run the thing too hard and loaded to the guwalls until a piston failed. He continued to run it hard on the mountain pull trying to get home until all the oil was gone.
Then to add insult to injury he ran the thing until it was pounding so hard that he just could not stand it.
Now this engine had about a quart of oil left in the pan along with all sorts of metal and other junk.
I started the engine up after filling it with oil. It ran fairly well but the oil pressure was very low and the poor thing was making lots of noise.
The rods were almost all gone and the mains too. The crank was beat to pieces but was not broken.
I removed the crank and then proceeded to whail on it with a large sledge hammer and never did break it. Hmmmmmm
Best
Robyn
Good rebutals. I agree with most of what y'all said. I don't really see the evidence pointing to oil breaking down or premature bearing failure expected with hot oil. Lots of stories with high milage units looking good internally and sudden unexplained crank beakage.
BUT I do think the oil temp is a little too warm on a stock 6.5 (at least working it). Light duty its probably fine but towing I bet the oil cooler is appreciably undersized. I thought I read Ronniejoe say he measured fairly high oil temps unexpectedly. Its probably is heavily dependant on ambient temps and cleanliness of radiator stack.
I'll have to ask my cousin specifically about what he was saying about the cam journal oil hole and what he has seen as I haven't seen many 6.5 cranks personally.
clipped.....
The 6.5 is a top oiler, meaning that the cam gets oil first and then from there the oil is fed to the crank instead of like some other V8's that feed the crank first.
Best
Robyn
I saw you say this before and while I believe thats what its called I think its a little misleading.
From my helm manual...
Oil flows from pump to cooler to oil filter to oil galleries. From the main galleries it flows to the camshaft bearing bores. The channel in camshaft bearing bores supplies oil to the cam bearings and feeds the main bearing oil galleries. Thus the cam bearings and the crank path are in parallel as much of the oil path is overall. Oil will flow in the path of least resistance. Probably yes at start up the cam will get oil first but I figure almost immediately a much much larger amount of oil flows to the main bearing galleries.
The first time I read you type oil goes to the cam then goes to crank sounded funny. I guess its kind of true but no I don't think oil goes to the cam then to the crank. Its a parallel path just a shorter one to cam bearings but smaller passage ways. Most oil goes towards the crank.
I don't mean to nitpick terminology but it just bothered me it may mislead. I would say really most all oil paths are in parallel and oil once flowing simultaneously oils everything.
Was the paths from channel in camsaft bearing bores to upper main bearings enlarged when oil sprayers and bigger oil pump were added? Might have been what my cousin was talking about??????
Bottom oiler or if you will, side oilers
The old Ford Hi Perf 427
The oil was directed from the filter directly to the main oil gallery in the side of the block and then to the mains and from the mains the oil traveled up to the cam bearings and then to the lifters and the top end.
The terms are fairly well ingrained in us "Old time" mechanics that have worked on performance engines from the 60's and 70's
The 6.5 has a central oil feed that feeds the cam and lifters first and then the feed goes to the mains.
The idea of the side oiler was to get the oil into the rotating mass first and then what was left over would be quite fine to keep the rest happy.
Many performance engines that saw the use of mechanical lifters would see the addition of restrictors in the feed to the top end as this tended to keep a lot of oil from pooling in the top of the engine during periods of high RPM.
Not an issue with the 6.5.
The flow of oil was not changed IIRC. The larger oil pump was added to make up for the huge loss due to the sprayers (Little built in leaks ya know)
I have seen front mains go away and am not sure what caused this other than a plugged feed from the groove around behind the front cam bearing.
The oiling system however not as good as it could be is probably just fine on the 6.5
Oil system failures on this engine family has not been an issue over the years that they have been built.
The crank/block issues are very much probably a harmonic issue that under conditions that are obviously created during some driving conditions.
It does not seem that the failures are agravated by power increases as so many of these happen to grocery getter Burbs and such.
IMHO if the temps had anything to do with the failures then we would be seeing bearing failures and this just has not been the case.
The failures are abrupt and catastrophic failure of the crank shaft through one of the main journals generally in the fillet.
The block cracking can be found in high or low mile units and it seems that hard use is not always a factor.
One of our members pointed out that the lower geared duallies that operate in the upper RPM ranges tend to see far fewer failures than do the tall geared passenger rigs (Burbs, Tahoes)
And on the speculation goes. :)
Robyn
Just typing here don't think I am arguing with anyone. Yeah, I guess it is a "top oiler" but it just sounds funny to me. I have worked on cutting tools that cut multiple features. Each blade or insert had a coolant directed at the chip sometimes long tools. As coolant entered the rear of the tool from the spindle or a coolant gland I just never thought coolant flowed from spindle to the first feature then to the next and to the end of the tool. To me coolant entered tool and exited all the holes at the same time. Some times coolant shot out the end of the tool and dribbled out the back holes if the hole sizes weren't correct. Oil path: size, restrictions, direction changes etc is complicated and I just did not want anyone to think the cam was getting more priority than the crank. Its just in the circuit first distance wise from the oil pump like the first sprinkler on a line but thats not to say it gets the most flow or anything. But thinking about it its not exactly in parallel flow either so I shouldn't say that.
I am just exploring thoughts. Like I said I have always wondered about oil capacity with the 6.5. Severe duty maintenance cylce is what 2,500 miles per GM. Thats pretty often for a diesel "work truck" (unrealistic IMO for a work truck). Probably soot related but just MAYBE? GM thought the oil would get too hot and wear out sooner. GM did later add the piston sprayers and increased oil cooler line size and oil pump capacity. I wonder what the compelling reason was otherwise they would not have done it. Low RPM would be less oil flow too???? But I do like the arguements against excessively high oil temp because not a bunch written about burnt bearings or oil etc.
I do think the oil cooler is an area worthy of upgrade for a high output and or towing engine.
Yeah, I don't think the oil flow path directions changed just maybe the size of the paths from the cam journal channels to the main bearing galleries when they added the piston sprayers. To offset the extra leak of the sprayers.
GM recognized the harmonics issues fairly early on, about the end of the run of v-belted engines they came out with a dampened lower v-belt pulley to help out.
Also with the A6 a/c compressor the v-belt got some length to it and some of the belts themselves would set up a nasty vibration on the top side from whipping up and down.
Had to tension them with care.
Merle
DA BIG ONE
12-26-2007, 04:16
Oil capacity can be increased by addition oil bypass system and larger filters if one desires.
Not being an engineer, I can only guess that smaller engines I've seen mounted w/rubber bushings on things like the AC compressor, alt, p/s pump, etc are there to reduce harmonics on crank resulting in a smoother/longer operating power plant.
We see GM's attempt to smooth thing out w/balancer and lower pulley assemblies being isolated by rubber, or?, on the 6.5.
Right now we have the option for the Fluid Damper to make things even smoother on the 6.5.
I remember someone herein the forums mentioning the forces upon the crank which could lead to crank failure when there is a miss, or stumble like so many 6.5's w/DS4 IP live with; This I think is the issue!
After reading posts here and mulling it all over and over. I probably misquoted theory he probably said maybe the crank was getting too hot (not the oil). But I guess its kind of goes hand in hand. And bearing health would also be related to crank temp so all arguements still apply. Again just food for thought. After all I have read I don't think there is a definative answer to crank failures but several contributing factors.
joe bleaux
12-26-2007, 12:45
On my 6.2m the a/c belt vibrated so bad and was so hard to adjust that I built an adjustable idler pulley to not only dampen the vibrations but to also make it very easy to adjust belt tension.
Joe
GM recognized the harmonics issues fairly early on, about the end of the run of v-belted engines they came out with a dampened lower v-belt pulley to help out.
Also with the A6 a/c compressor the v-belt got some length to it and some of the belts themselves would set up a nasty vibration on the top side from whipping up and down.
Had to tension them with care.
Merle
The 6.2's in the early days of the 6.2 there was not any dampening systems on the lower belt pulley. The late 6.2's and then the 6.5's have a rubber isolator built into the pulley to damp this stuff out.
This very harmonic is what we have discussed in depth on the various threads here regarding the block and crank issues.
The 6.2's in many applications came with a stainless steel shoe to protect the upper radiator hose from being sawed in two by that vibrating long belt.
The Old 5.7 was also very bad about that same vibration.
later
Robyn
joe bleaux
12-26-2007, 16:20
I THINK my '84, 6.2 van, has the dampener. I will verify this when it warms up. I did look before and saw a thick wheel about the same size as the 6.5 dampener. That wheel runs true yet, before I made the idler/manual tensioner, the belt swung wildly and often broke.
Joe
The 6.2's in the early days of the 6.2 there was not any dampening systems on the lower belt pulley. The late 6.2's and then the 6.5's have a rubber isolator built into the pulley to damp this stuff out.
This very harmonic is what we have discussed in depth on the various threads here regarding the block and crank issues.
The 6.2's in many applications came with a stainless steel shoe to protect the upper radiator hose from being sawed in two by that vibrating long belt.
The Old 5.7 was also very bad about that same vibration.
later
Robyn
I did post awhile back my theory on the intermittant missfires stressing the crank & block & I still feel this is a big contributing factor. Did crank & block failures rise significantly in 94 with the release of the electronic pumps? Another of my theories is the rubber crank pulley isnt there to help longevity of the crankshaft so much as the belt. Diesel engines in general give me the impression that the rotation stops & starts four times per revolution on a v-8 style engine, hence the dual mass flywheel on manual trans trucks. I think the dual mass setup is to save the trans, not the engine. I bet a lot of the engines with low miles crank & block failures are also the ones that have had multiple injection pump repacements as well. I think i stated my observation last time about the number of 6.5s i have seen with the original injection pump at super high miles and they never seem to have any problems, while the ones that have been warranteed one or more times seem to be the ones with major structural problems.
Bingo
All the things you are talking about cook up a wonderful batch of HARMONICS and therein lies the culprit. It will tear things apart with ease given the right amount of time.
Having a poorly maintained engine with a set of sour injectors that may be causing some missing or poor/weak power pulses on some cylinders.
Crappy Ip that could possibly be producing similar conditions.
The engines that are not seeing low speed pulling seem to do well.
All great ideas but can we ever prove exactly what kills these engines.
Hmmmmmmm I surely dont have the complete answer.
We have some pretty good engineers that frequent this board and I have swapped theories with many of them and the jury is still out.
Harmonics is a killer for sure.
The frequency is the key me thinks. If certain particulars in the engine such as the state of tune and possibly even mechanical tollerances ect may allow one engine to run in a little nitch that does not see the killer harmonics form.
If the harmonics are setting up and these are at a frequency that matches the critical frequency of the block and or crank the stage is set for catastrophic failure to occur, its just when.
The vibration dampener should be able to snuff this stuff out, key word is SHOULD.
I have owned many 6.5 powered trucks and most have a particular feel and sound to them that is similar.
The 95 DaHooooley 3500 4x4 I have now, does not run, feel or sound like any of the others I have owned. It is very smooth, quiet and runs with so much different sound and power than any of the others. Feels like a very strong BBC under the hood.
I have no answers as to why
Keep the topic going and one day we may all get it figured out :)
Later
Robyn
I'm a reformed lube engineer. The theory of failure due to "over temp oil" is patently bogus. If oil is heated above its breakdown temp (typically ~350°F), the cause of the overheat is the culprit, not the oil temp itself.
Things like failed harmonic damping shouldn't cause overtemp of the lube, but can cause other failures nevertheless. Intermittent injector firing can also cause a similar issue.
All that said, oil temp does need to be controlled; on the AMG 6.5L TD in my motorhome, I installed an external oil cooler (the previous one was integral with the radiator, and used 3/8" hoses; the external uses 1/2") and I added a fan (mainly because of airflow in my diesel pusher).
While the 6.5L TD is a decent engine, it's not designed nor produced to the same criteria as a Cummins (5.9L or 8.3L) or Cat (3116/3126 and up); those latter can tolerate more abuse (like misfires), in part because they're oversquare (long-stroke) engines designed to operate at around 1,200-1,600 RPM, where max torque occurs. The GM/DD/AMG 6.5L TD is a short-stroke, with max torque occurring at 2,400-2,600 RPM.
I am a little embarrassed I miss communicated this theory and took it off on a tangent. However it is a little related.
I don't think it is a definative route to failure but just pondering things "the crankshaft getting too hot" may have SOME merit.
Just thinking this possible scenerio. GM did not make a good call on the block material so in my mind the crank material could be suspect too. The OE GM crank was some ductile cast iron that is forged to shape then machined. This cold working forge process makes it "stronger" (on edit "stronger" not tougher really its just increases its yield strenght due to the "prestraining" of forging. I can't remember the curve I think ultimate yield strength remains realitively the same) than it would be in annealled state. Now you heat it up and vibrate it which could destress and negate some of the cold working benefits. After some time you are left with a weaker crank that just adds to the problems of harmonics and not as rigid block as desired, and other bad combustion timing issues.....etc.
How hot does it take WITH Vibration to "anneal" the material I don't know and how hot does the crank get I don't know. Just thinking turbo diesel and really hot piston and hotter bottom half of engine vs a gasser just maybe it was a learing curve for GM. Again they added the oil sprayers, bigger oil lines, and bigger oil pump. Was it some attempt to help engine durability and or help with a cooling problem. I think so.
Reading the article in Maxx Torque about oil temperature in the Duramax reaffirmed some of my concerns of oil temperature in the 6.5. No its not the same but I still see some relation.
I do believe the oil gets really hot. Maybe momentarily that it can tolerate but still it gets hot.
Just thought I would post something different and converse about it.
If the oil gets "momentarily hot", there's an underlying issue at the location of the overheat. Overheated oil, especially the paraffinics in contemporary motor oils, when subjected to severe over temps, tend to produce gritty carbonaceous deposits, not good. Nevertheless, that type of extreme breakdown isn't oil-related - it's a symptom of something more critical in the engine internals.
If the crank bearings are overheating, there's an underlying issue unrelated to the lubricant.
Yes and No. I do think its at least related to the lubrication. The oil is the "coolant" for the bottom half of the engine. It lubricates and helps dissipates some of the heat from the piston, crank, cam, turbo, rocker arms etc. How hot does oil get in the engine I don't know its exposed to really high temps for short periods. The upper rings of the piston can approach what 600-800F. Cam bearings can approach what 400F?. The turbo could be what 600-800F again. Not too hot for metal but all of those are above 350F oil break down temp. BUT oil also dissipates this heat back into the block immediately (and or doesn't absorb all the heat). The block conducts heat back to the engine coolant and radiator expells it to the environment. Because of this heat dissipation its impossible? to measure the momentary temperature of oil. A sump probe or most any other location is just going to pick up the average temperature.
I can pass my finger through a candle flame but don't melt my finger, if I go too slow it burns like heck, and if I stopped you get the picture. So time at temperature is a major factor too. This time factor is what keeps oil from breaking down and more so the dissipation of heat back into the block. For sure if shut down hot a turbo can coke oil. The blocks mass is probably what saves the oil on piston rings and other hot spots on a hot shut down. Motors that burn up hot and fail do coke oil in places don't they? At least I think the crud I have seen in some bad motors is coked oil. But normal temps very little to none breaks down and if a little does breaks down its probably dispersed with additives and all the other crud - soot etc???
I am willing to bet if you took all oil cooling off a hi output truck 6.5 oil break down would be a problem and reduced heat dissipation could contribute to lower engine failure: piston gualling and maybe spun bearings etc if you worked the engine really hard. I don't think it would lead to a crank failure right off (if not bearing problem) but over time does the crank "anneal" some and get weaker ????? Thats the only merit I can see to the "crank getting too hot" and just post it as maybe a contributing factor and food for thought.
You're on the right track - oil breakdown due to overtemp is a symptom, not the cause. Those temps you indicate are a bit (to way) on the high side, but you've related the reason - the need for oil to cool the lower end of the engine.
An internal-combustion engine lube is tasked with the following:
Lubricate
Cool
Seal
Clean
Protect
The main cause of engine failure is heat (shut off the lube flow, the bearings spin - because the heat welds the crank to the babbitt). Lubrication prevents heat from friction. Cooling removes heat from areas where otherwise it would accumulate. Sealing prevents blow-by and increases engine efficiency. Cleaning keeps all of the first three working as they should. Protection keeps condensation in the engine from corroding expensive parts.
The cam bearing temp is too high (at least for a roller cam & lower diesel rpms) it was just a guess with a ?.
Most of the turbo heat is dissipated through the intake air and/or radiated out. Not all that much oil flows through the turbo anyway and I think its whipped to a foam from the really high RPM's.
But yeah the upper rings and crown of piston can approach 600-800F I have read and believe. Maybe not daily driving light throttle. But I can push 600-750F EGT in the wind on the interstate unloaded with my mods in the summer.
Summer time towing or an unhealthy truck could easily see 900-1000F EGT's, 200-210F coolant temps, and IAT's of 200F?. So oil being exposed to really high temps is a real possibility.
...Most of the turbo heat is dissipated through the intake air and/or radiated out. Not all that much oil flows through the turbo anyway and I think its whipped to a foam from the really high RPM's...
I disagree. In my experience, copious amounts of oil flow through the turbo center section, primarily to cool it. Just look at the size of the oil return line...
I thought the return line was so oversize because the turbo's seal is more like a labrinyth type seal (because no conventional seal material will stand up the heat and rpm's). The oversize return is to ensure there is no appreciable pressure on return line and allow the foamed oil plenty of room to expand, defoam, and drain back to pan.
I could go either way I think air cools it and oil too. Not sure which does more.
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