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Old 09-23-2003, 03:12 PM
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Join Date: Jul 2003
Location: Mirabel, Qc, Canada
Posts: 9
350 Sdl, 1991

Hi or should I say HELP!
I just had the head gasket changed on my mb: $1,800.00
I still have the same problem which is motor oil in cooling system. Also, I have to keep adding coolant on a daily basis and a quart of oil every 1500 km. I also noticed a lot of pressure building up in the cooling system. Upon doing the head gasket the mecanic says that they inspected the head visually for cracks and saw none. I have the feeling that he did not do a thorough job and that the head is, indeed, cracked. Today I noticed the temperature gauge at 120 and I stopped immediately. It coudl not have been at 120 for very long but now after the car is stopped for more than 30 min. there is a puff of white smoke when I start the car. The mecanic wants to redo the job and send the head to be x-rayed but he is going to charge me again. I say enough bull and will do the job myself with the help of an old friend and very good mecanic. Is there something I should know before I start the job. I am sarting to hate the car and it's too bad as the vehicle is in very good condition. Can you give me some advise.
Thak you,
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Old 09-23-2003, 04:14 PM
I told you so!
Join Date: Jun 2002
Location: Motor City, MI
Posts: 2,741
Visual may not be enough. I don't know how x-raying can help - that's more for casting porosity, not cracks. I'm sorry to hear you spent all that money only to be back at square one.

The high coolant temps indicate exhaust leaking into the coolant. White smoke indicates coolant leaking into the combustion chambers. Oil in the coolant may be related or it may be a different leak. You didn't mention whether the head deck surfaces were checked for flatness or corrosion. This would be the first step when it's apart. Some people go ahead and skim (or shave) the mating surface anyhow. If that checks out okay, then you'll have to start looking for cracks. I imagine the diesel heads are made of iron. This would make them good candidates for Magnafluxing. A good shop should have this machine which checks ferrous parts for cracks.

If the head is aluminum, critical areas can be checked by liquid dye penetrant methods. One leak path not visible in aluminum heads is between the valve seat counterbore and inner water jacket. Only pressure testing can uncover this leak path.

Another possibility for leaking can come from a cracked bore in the upper part of the cylinder block.

So basically, when you have the head off you need to clean both mating surfaces, check for flatness, and keep inspecting the related parts until you find the leak path. And don't give up until you find the problem. Once fixed - and you can probably do a better job than the mechanic - you'll feel good about the car again.
95 E320 Cabriolet, 131K
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Old 09-23-2003, 09:49 PM
sixto's Avatar
smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 18,745
A statistically significant number of 350SD/L engines succomb to connecting rods which bend causing the cylinder bores to wear in an oval pattern and other such unpleasantries. I'd look for a tech with specific experience with the 603.97x motor and lots of it. He'll be able to tell if your problem is cracks in the head or bad connecting rods. Hint, an MB dealership is probably not the best place to go looking for this tech. I think it's a worthwhile gamble to get a $200 opinion before throwing another $1800 at potentially uneccessary cylinder head work.

FWIW, when the head of my 87 300SDL had cracks, coolant consumption was not so bad, temp would go to 120 quickly and there was tremendous pressure in the cooling system. Idle was pretty bad but the car was driveable. No mixing of oil and coolant. It was easy to see the cracks in the combustion chambers.

Lots of info for you if you use the search feature. I'm sure someone in the Diesel Discussion forum can recommend a tech in your area.

BTW, removing and replacing the cylinder head is not a particularly difficult job.

95 S420
91 300SE
87 300SDL
83 300SD
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