My car is a crackhead
 

Cast iron heads can & do crack -- a problem that is more prevalent, yet apparently not limited to, the aluminum heads

This post is meant primarily as a follow-up to prior threads about recurring hot running & rough running problems with my 84 300D (now with ~206,000 miles). I hope that people searching through the archives looking for information may learn from my experience.

A (not so) brief recap: during hot weather last year my car exhibited signs of running hot, yet not severely overheating. A thorough refurbishing of the cooling system helped to reduce the temperatures, but it still ran warmer than normal -- usually in the range of 87 degrees C and up to a maximum of 102 under heavy loads and high ambient temperatures.

Diagnostic procedures were inconclusive. Compression was very good with only the two rear cylinders showing any signs of deviation, both being approximately 20-25 PSI lower than the front three. Doing a leak down test (audible only) indicated no problem.

One time, and one time only, I noticed just the slightest hint of an oily film floating on top of the coolant in the reservoir -- not even enough to form a droplet. I correlated this with the lower compression on the two rear cylinders and concluded that the head gasket was beginning to let go. Although it is not generally considered standard procedure to do so, I re-torqued the cylinder head bolts & thoroughly flushed the cooling system. There was never again any hint of oil in the coolant. I knew that this was a temporary fix, just to buy some time.

More recently it had developed problems with misfiring for a few seconds upon startup, difficulty starting while hot, accompanied by excessive gray smoke (from partially burned fuel -- not steam). Being that the compression is good, & I was not losing any coolant, this seemed like a fuel delivery problem. I resealed the delivery valves in the injection pump, checked pump timing, & installed new (rebuilt) injectors to no avail.

One thing I had ignored is that the cooling system remained pressurized after sitting overnight. I was not losing any coolant, and I had read several threads where people had indicated that their diesels did the same thing & this was normal -- nothing to worry about. This always seemed wrong to me, however being a novice with diesels I simply let it go as being an idiosyncrasy of the 5-cylinder diesel engine.

Then about a month ago I did start losing coolant, albeit slowly. There were no external leaks so it was obvious where the coolant was going. There were no indications of coolant contamination in the oil -- the coolant was going into the combustion chambers while it was running, but the system would still remain pressurized after sitting overnight. I figured that the combustion pressure pushed its way past the gasket into the cooling system, but it was still tight enough that the relatively lower pressure in the cooling system didn't push the coolant back through to the cylinders, at least while it was not running, thus the remaining pressure in the morning.

As much as there is one neighbor that I don't mind pissing off too much (:p), it became rather embarrassing to fumigate the neighborhood (especially when it isn't mosquito season) -- so due to the excessive smoke problem & now the coolant loss, I decided to bite the bullet and pull the cylinder head. Boy, was I in for a surprise. The cylinder head had numerous cracks -- in between intake & exhaust valve seats, and also between valve seats and the pre-chambers. Needless to say, that casting has no value now, other than as a boat anchor.

So… a word of caution to those of you with a cooling system that remains pressurized overnight – it’s NOT normal. By ignoring it, you may cause more damage in the long run. I believe that in my case the head gasket started leaking into the coolant -- this accounted for the residual cooling system pressure in the morning. By ignoring this symptom I created a chain of events that led to greater damage. My hypothesis is that the combustion gases forcefully displaced the coolant in the cylinder head, leading to localized overheating, which in turn caused the severe cracking of the cylinder head. IF I had not ignored the ‘residual pressure in the morning’ symptom, I may have gotten away with a simple change of the head gasket (personally, I would do a valve job once the head is off no matter what) but instead, my cylinder head had to be replaced. Oh well, live & learn… I just hope that this can save other people from having to learn the hard way.

RTH

P.S. I've obtained another head, had it completely rebuilt, and I will be installing it during the next week along with a new timing chain, rails, various seals, all the small coolant hoses, etc., etc.

RunningTooHot:

Sorry to hear that you had to find out the hard and expensive way that your head was cracked. I and, I would guess, others would be interested in the reason(s) why the head cracked. Did you inspect the old head gasket to see if it shows signs of allowing coolant to pass into the cylinders? Or, are there clear round circular impressions left by the head gasket on the head (these would be from the metal reinforcing ring and gasket adhesive) or are the circular impressions partially missing in places (like between cylinders and where the water jackets are located between the cylinders)? Reading the old gasket and the components that were sealed by the gasket is a vital key to determining why a failure occurred. If the head gasket was leaking coolant into the cylinders, then that may be why the head cracked since water does not compress and given the very tight piston to head clearance (to get the 21.5 to 1 compression ratio) the water could have caused the damage to your head.

Or, did the head have a flaw from the factory that eventually worsened to cause the damage you experienced?

Or, was the engine really over-heated sometime causing the initial leak leading to the failure (your minor running hot symptom does not sound like it is enough to cause a head gasket leak/failure)?

Or, was there too much boost from the turbo?

Or, was there something else that caused the failure (like failure of the head bolts)?

You may know that pre 1979 300D's had a head gasket problem that was fixed by M-B in 1979 by using a new head gasket design, using torque-to-yield head bolts, and harder head bolt washers.

Finding and understanding why your failure occurred is key to avoiding the same problem in the future.

Good Luck!
Tom

Hello Tcane

The exact service history of this car is unknown other than it was maintained at a couple of local MBZ dealerships. It was owned (literally) by a little old lady who kept it in truly exceptional condition – it is one of those original paint, unmolested ‘time-warp’ cars that was obviously garaged & lovingly pampered, which is one reason that I decided to buy it. It had 197,000 miles on it when I bought it last June. I will have to assume that the car did overheat severely at some point prior to my ownership – that would be the only explanation as to why the cylinder head gasket would begin to fail at such low mileage.

Yes, I did inspect the head gasket – you are right in that it tells quite a story. Apparently, the leakage started at the rear of #5. It seems that while the engine was ingesting small amounts of water & burning it, the resulting steam eroded the upper section of the cylinder liner on the rear of #5 cylinder. The steam ate away about 1/4 of the thickness of the liner at the very top. There is evidence of similar damage in a couple of other cylinders, but not nearly as bad. On several cylinders, the steam also ate away at the vertical edges of the aluminum sealing ring that is integral with the head gasket, so when it was removed, it seemed as if there were two separate rings – one on each side of the gasket, rather than one piece wrapping from one face to the other. The rings separated from the body of the gasket, so there definitely was inter-cylinder leakage, especially between cylinders 4&5.

Addressing your list item by item: The amount of coolant loss was not at a rapid enough rate to have caused hydraulic lock, so that is not the reason that the head cracked. The head bolts were not the cause – they are within specification for length, so I will actually be reusing them. With this vintage of MBZ, quality control should not be an issue - it seems highly unlikely that there was any casting flaw from the factory, so we can rule that out. There was not “too much boost” from the turbo – I previously adjusted it to spec, plus there is overboost protection built in by the factory (if there is too much boost, a solenoid valve opens which dumps the boost signal going to the ALDA, reducing fuel flow, effectively reducing exhaust energy & therefore turbine speed).

As I said earlier, I believe that unless this is just a fluke, the engine must have been overheated severely at some time – perhaps a radiator hose let go on granny some time ago.

I hypothesize that once the combustion gasses were able to escape into the water jackets of the head, the gasses pushed the water out of the cylinder head passages – this allowed certain localized areas of the head to become severely overheated, which then lead to the cracking. This is conjecture on my part, but again, it seems quite logical.

As far as head gasket design is concerned, there is still a significant difference between manufacturers. The first gasket that I got was a Reinz – I was NOT impressed with either the design, nor the (lack of) quality control. Needless to say, it went back to the supplier. The Elring gasket has a lot more meat to it – there is metal reinforcing between cylinders in addition to the normal sealing rings, plus it is readily visible that the quality control is better – the sealing rings are more symmetrical vs. the Reinz. I’m sure that others may disagree; some people are blindly allegiant to brands – such as is the case when people start discussing motor oils….

Thanks again for your reply… I hope that this information will be helpful for others out there.

RTH

RunningtooHot

Thanks for filling us in on the final answer. I followed your saga with great interest. I find all electrical and thermodynamic car problems very interesting.

I think I mentioned it before, but somewhere you can find a device that will detect the presence of combustion gasses in the coolant.

In 20/20 hindsight, that might have saved the head. However it could have been too far gone anyway.

Again, thanks for the "closure".

Let us know how the repair goes.

Joe

RTH,

You mentioned steam damage to the cylinder liners. Are you talking about the head gasket cylinder liner, or the liner in the cylinder block? I have the same problem, on both my newer aluminum-headed OM603's. You probably read my threads (and myoder's too) about this. I've heard the water/steam can damage the cylinder liner and either require a new liner, or if it's bad enough, a new block. (!!) I'm trying to figure out if this is possible or just more urban legend. If you could elaborate on your finding that would be great!

Oh, one last thing - how long was it between when you first noticed something amiss, until you yanked the head (in miles and months)?


Best regards,

Gsxr:

Both. The head gasket sealing ring was eaten through at the vertical cylinder interface, and a few cylinder liners also had varying degrees of corrosion damage at the top of them as well. The worst was on No.5, where the liner was eaten through about one-quarter of the thickness of the cylinder liner at the very top/rear. (I'm crossing my fingers that the new head gasket will still seal effectively -- it looks like it should.)

I have had the car for approximately 10,000 miles – the overheating problems were apparent soon after I bought the car, which was in June of last year. Summers are hot here, with 100+ degree days at the peak. This is my first diesel, so I was not familiar with just how warm/hot they are expected to run; nor how well they should run when they are running properly. No doubt, my ignorance exacerbated the problem.

On my engine, the corrosion was limited to the vertical bore of the cylinder liner, extending up to, and including, the very edge at the block/gasket parting face. The top (horizontal) surface of the block & remaining ¾ thickness of the liner are not damaged, which is why I am assuming/hoping that the new gasket will still seal it effectively.

Could you please elaborate about the damage that you experienced? I am curious about the severity & location of your damage.

RTH

Ooops, sorry about that - I meant I have the same issues with pressure when cold, losing coolant, etc. I haven't removed the heads yet to inspect.

I just placed what hopefully will be the last part & tool order from my favorite part supplier (rusty.mbz.org), with all the stuff I'll need. I'm going to try the job myself and I bought some of the special tools needed, like prechamber pin wrench & puller (Baum Tools), and other little stuff. I got the gasket set and other items as well. I have a baaaaad feeling that the head will be cracked, won't know until I yank it though. A BARE head for my engine is ~$1500! (plus valves, seals, labor to swap stuff from old head, etc.) I'm hoping I have minimal, or zero, liner damage.

My one car shouldn't have liner damage, as the coolant level just recently started dropping (less than 1kmi.) The other car has been doing it for at least 10kmi, maybe longer. Long story on that one - it runs great otherwise, so I've been putting it off. I hope that delat doesn't bite me, I'll be pretty bummed if the liners are destroyed from 1-2 years and 10kmi+ of operation with the leak! :eek:


Keep us posted on your project, OK? I'm curious as to what happens. BTW, a mechanic at the local stealer has a 300SDL (OM603) and even after the NEW head and gasket, he allegedly still had pressure when cold. I hope I don't, I'll be pretty ticked off if I do!

Best wishes,

What you said about the new 603 head that still leaks doesn’t surprise me – apparently the machine work on the new head castings is not very good.

The only person that I trust *implicitly* with all the machine shop work on every MBZ engine that I have ever had (and many other friends as well) told me that oftentimes they need to re-work the new 603 castings to get them to be spot-on. And he really *knows* MBZ engines due to years of re-manufacturing experience, plus he is a straight shooter – no B.S.

Good luck on your project – keep us all posted, and I’ll do the same…

RTH

RTH,

I also have an 84 300Dt and have a very similar temperature issue that you described. Some other questions:

1. What was your fuel milage?

2. Did you experience any nailing or light thudding at lower engine speeds from the affected cylinders?

3. Anything strange when you started the car in the morning?

4. Did it effect performance?


Thanks.

Gsxr:

I went over to the get some miscellaneous parts for my engine at the machine shop/ engine rebuilder, and he showed me a brand new 603 cylinder head casting. It truly was in need of some rework. The bottom surface was not smooth the way it should be when it is surfaced properly. Instead, you could see & feel (!) the rough surface left by what appears to be a fly-cutting process from the factory. There were other rough areas as well - this can be a stress riser leading to cracking in the future. I couldn’t tell by looking at it, but I was told that they usually re-do the valve seats as well. All in all, not very impressive. It is obvious that whoever is doing the castings for MBZ is not using the same QC standards as MBZ used to have. Sad. Very Sad.

It would seem to be a prudent move on your part to have someone that is *really* knowledgeable about the particulars of these engines do the machine work for you. Using the head casting ‘as is’ does not seem like a good idea at all.


Dieselnation:

You may want to use the ‘search’ function (type my name in) to look at prior posts that I have made regarding the problems.

To answer your specific questions:
1. Fuel mileage was usually around 23-24 mpg when I first got the car, dropping down to around 22 as time went on. I have a heavy right foot.
2. I’m not sure about the nailing or thudding, as I don’t have a valid point of reference – this is my first diesel, so I don’t have anything to compare it to.
3. Morning starts became rough, with misfiring for 5-10 seconds, even with extended glow periods. Note that the coldest it’s been is in the 40’s (up until just the last week, at least). Strangely enough it was HOT starts that gave me the most problems, with extended cranking needed & then a cloud of gray smoke from partially burned fuel (not steam, as the cloud did not readily dissipate).
4. Affect performance? Again, I have no point of reference as to what a properly running diesel should be like.

Thanks again guys…

RTH

I think I am going to pull the head on the 300D over the next month or so. I doubt if it has ever been off. The 240D is getting to the point where I can use it for a daily driver.
Anyone want pictures of anything in particular?

lest we forget.

Is this issue more dependent on temperature range?

or just high temperatures?


I replaced a head gasket that was beginning to fail, but the head was fine. Does the failure of a headgasket impact the potential for a cracked head? How so?

I replaced a head gasket that was beginning to fail, but the head was fine. Does the failure of a headgasket impact the potential for a cracked head? How so?[/QUOTE]

Logic that the leaking combuston gasses might form an air pocket by displacing the lower pressure coolant flow in a given area resulting in a hot spot. Repeated many times could cause a crack by the difference in expansion and contraction of that portion of the casting. Most the time fortunatly this does not happen to the extent of damaging the cast iron head.