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.

I wondered what had happened to you.
I thought I had resolved the pressurized cooling system problem with my 300D but it still remains pressurized overnight occasionally. It seems to have alot to do with ambient conditions. When it is cold it seems to retain pressure. Then when it is hot (low 70's dF like it was today) it does not retain pressure. Anyway, when I got home this evening I removed the cap and relieved the pressure. Later on (I again opened the cap and it was almost as if it were pulling a slight vacuum which is what I should have seen seeing as how it was cooling down) I went out, cranked it up and ran it for a few minutes to see if it would build pressure in a real short period of time it did not. I would think that if it had a cracked head then it would build pressure almost immediately after starting.
As long as mine runs good, does not smoke, does not loose coolant or oil I think I am going to keep running it. The recently rebuilt 240D does not hold pressure overnight nor does the Honda or E320 (nor any other car I have ever owned). I'm wondering if the cooler temperatures would allow a crack to "open" more - I don't know. Funny thing about it is that the car runs great and the coolant temperature stays between 80 and 90 dC when up to temperature - based on traffic or highway. It does not miss or smoke and I am not loosing coolant.
I have been considering pulling the engine at around 250k miles and going through the top end rebuilding the tranny and replacing all the chain guides at the same time.
thanks

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Jim

Hey there Jim…

I’ve been lurking around here looking at postings from time to time, but between being sick for a few weeks and being really busy trying to catch up on some projects, I haven’t really had time to participate in the forum during the last few months.

I’m not quite sure how the ambient temperatures would affect the leakage, such as you have observed. However, a word of caution: when I first noticed the residual pressure symptoms I did the same test (letting out the pressure & then starting it up to see if pressure built up quickly). The pressure did NOT build up immediately. At that time, I was not losing any coolant, or misfiring &smoking excessively at startup either. I now believe that it took higher peak cylinder pressures (running at load) to force gasses around/past the gasket. In other words, I wish that I could alleviate your concerns about your car, but I cannot.

It seems logical that you may be at the early stage of head gasket failure, such as where I was at a few months ago. This may explain why the residual pressure problem is not (yet) consistent on your car. I think that it would be prudent to take preventative measures now. I believe that while I was continuing to run the engine, the combustion gasses pushed the water out of the cylinder head passages – this allowed certain localized areas of the head to become overheated, which then lead to the cracking. This is conjecture on my part, but again, it seems quite logical.

So it seems that if you were to pull the head now, it is less likely that it is cracked, but if you continue to run it, who knows….

Another problem that I did not mention in my previous post – 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 (vertical surface only - the top of the block is fine). There is evidence of similar damage in a couple of other cylinders, but not nearly as bad. 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 head gasket overlaps the liner area quite a bit, so I am crossing my fingers that it will seal effectively enough for me to get at least another 100,000 miles out of her. The corroded area is well above the point where there is any ring contact, so at least that is not an issue. I just finished chasing out the head bolt holes tonight – I called it quits when I got to looking at how to get out the pivot point bolt that holds the banana (tensioner) rail in place. It is a press fit, but the mickey-mouse puller I made for the smaller type pins (used on the upper guide, as well as on the V-8s) won’t work on this big one. This plus I have to figure out how to jury-rig something to press the front crank seal into place… lots of work to do…I just hope that Murphy isn’t hanging around to ‘assist’ me…

RTH

On the 240D I used an appropriately sized bolt and some flat washers (with the harmonic balancer in place). Put the flat washers against the harmonic balancer where it is "cut-out", screwed the bolt into the pin, tighted and then kept adding flat washers until the pin was out. Worked pretty well but make sure you have enough threads screwed into on the pin. I don't think you can bend/distort that harmonic balancer doing this - I didn't. I am going to drive the car a little while longer and verify I still have this situation. I kinda/sorta hate to pull a head on a good running engine but do, deep down, feel it should not hold pressure over night. I probably caused the crack myself when I changed the coolant one time and did not get all the air out of the system, drove it and the needle approached, but did not get to, the red mark on the temp gauge. The crack probably occured when I added the water later without letting it cool down enough - oh well - live and learn.
I will say that there was a crack in the head of the 240D above the bad #2 cylinder when I started on it. Wonder if that caused the problems with the cylinder/piston being ruined.
Where did you find the head?

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Jim

Jim,

Thanks for the tip on removing the pivot pin. I ended up using a very large flat washer resting on two of the 13 mm bolts going into the engine block as supports -- I wasn't comfortable with the idea of using the harmonic balancer, plus I already had it off to replace the front seal.

I agree with you that it is a distressing thought to pull the cylinder head when the engine is apparently running well. However it sounds like you are making an assumption that the cylinder head is already cracked; this may or may not be the case. It could just be the head gasket leaking at this point. The problem (as I see it) is that if you continue to run the engine you greatly increase in the likelihood that the cylinder head *will* be cracked once you remove it.

There are three approaches you can take:

1. Drive it until it drops – meanwhile looking for a good solid used engine to replace yours.

2. While you're still driving your car, start looking for a cheap cylinder head core to rebuild with the assumption that yours is already cracked, and drive it until it drops -- at this point you may have severe corrosion in the cylinder liners due to steam damage, in which case you are *possibly* back to option No. 1, or a complete rebuild. (On my engine the No. 5 cylinder 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.)

3. Bite the bullet & pull the head now before additional damage has a chance to occur. With 20/20 hindsight, this is what I would have done had I known better at the time. I can make excuses about being a first time diesel owner & not really knowing how well a diesel should run *when it is properly running*, but I hate making excuses. Please learn from my ignorance and save yourself from additional grief & $$$.

RTH

I think all I had was a weak headgasket.
Here is a pic of the cylinder head. I have not seen any problems here or the lower end. I will look rear good at the head while it is off - maybe new guides, seals, etc as necessary.

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Jim

Should the head gasket be replaced at 200K miles as a normal maintenance item? Mine runs close to 100 degC and I was going to try an AutoZone thermostat. Now I wonder if it could be the head gasket? Not that I do much of my own work, but I was going to ask my mechanic about it; any thoughts appreciated.

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Bob Roe
Lehigh Valley PA USA
1973 Olds 88, 1972 MB 280SE, 1978 Datsun 280Z, 1971 Ford T-Bird, 1972 Olds 88, 1983 Nissan Sentra, 1985 Sentra, 1973 230.6, 1990 Acura Integra, 1991 Volvo 940GLE wagon, 1983 300SD, 1984 300SD, 1995 Subaru Legacy L wagon, 2002 Mountaineer, 1991 300TE wagon, 2008 Murano, 2007 R320CDI 4Matic 52K, some Hyundai, 2008 BMW 535xi wagon, all gone... currently
2007 Honda Odyssey Touring, 2014 E350 4matic

Being a novice at best, I don't quite understand what you are recommending. I thought you stated that if you would have replaced the head gasket, you could have avoided the head cracking in so many places. How can replacing a head gasket prevent this and if you already have a system that stays pressurized overnight, and that's an indication of a cracked head , isn't it too late anyway at that point? Please explain., also, my diesel remains pressurized overnight for some reason as well. I mean, when I take the rad cap off the overflow tank, it lets out a belch of pressurized air too. Does this mean I have a cracked head even if I have no signs of other problems? I know the radiator was replaced before I bought it.

Yours is an aluminum head versus the 300D's cast iron head. The aluminum is less forgiving to being run hot (I wish I could find a cast iron head for the E320 ).
On my 300D all I did was remove the head, have it magnafluxed, cleaned, replaced the valve guides/seals and machined. Reassembled everything and since that time I do not have a pressurized system overnight. The car started and ran great prior to doing this and I did not have any overheating issues.
I think on yours the radiator being replaced should raise a red flag. I hear tell that there are places that can determine if there are products of combustion in the coolant reservoir.
It is my opinion that these cars can continue to run good for many miles with a coolant reservoir that remains pressurized overnight BUT on the same hand I am unsure of what long term damage, if any, may be going on with the head.

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Jim

Thanks much for the heads up Jim. Maybe I will have this done. By the way, what is magnaflux? Thanks again.

Nevermind, looked it up in search. Sounds like welding of some sort.

Magnaflux is a non-destructive test process used to find really small cracks that the naked eye can't see. It is based on magnatizing the area to be tested and does not work on non-ferrous material.

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Jim