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  #1  
Old 04-07-2009, 09:35 PM
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My mecahnic is stumped...oil problem on my 1992 300SE

Hi, I have a 1992 300SE with the 3.2 motor. It has 90,000 miles on it and I have a problem that I'm hoping you guys can help me with. A few weeks ago I noticed a good sized oil spot in my garage right under my passenger side front bumper. I opened the hood to find what I thought was coolant coming out of the overflow tube of the coolant reservoir. Upon closer inspection, it looked to have an oily consistency to it, so I took the cap off of the coolant tank. I found the brown, oily milkshake consistency in the tank, showing oil getting to the coolant.

14 months ago I had the head gasket replaced by my local mechanic. So, I immediately called him and told him what the problem was. He was surprised that it had happened and I got the car to him the next day. When he looked at it, he found that the engine oil was down almost two quarts and that a good portion of that oil was in the coolant tank. The oil on the engine dipstick was clean (ie. not the milkshake consistency of the oil in the coolant tank). He suggested two things: the head gasket had failed for an unknown reason or the oil cooler had become defective. He recommended that the cylinder head be removed to check the head gasket and also test the oil cooler. I said ok and he started the work.

Once he got down to the head gasket, he called and told me that everything looked fine (ie no visible compromise of the head gasket) and then he said he tested the oil cooler and said that it was fine. At that point he said he was puzzled, as those were the two main reasons oil could leave the engine and make its way to the coolant. Other reasons he gave, although more rare, were problems internally with the head or engine block. So, he put a new head gasket on and put everything back together. After flushing the oil and coolant a few times, he discovered that the same thing was happening...oil was getting into the coolant reservoir again and the oil level on the dipstick was approximately 1-1.5 quarts lower.

So, at this point my mechanic is recommending a new engine. I'm concerned that the original oil cooler that he tested could still be defective even though it passed his test. I have asked him to stop working on the car as I am concerned this problem might be beyond the knowledge of this mechanic.

So, my questions to the forum are, can there be any other reason for oil entering the coolant other than the failure of the head gasket or the oil cooler? And, what are the chances that an engine with 90,000 miles with no history of overheating or neglected maintenance would have cylinder head or engine block failure? And, can an oil cooler that passes a leak test still be defective once subjected to the operating requirements of the engine? The car is a cream puff and I want to save it, but I'm in this diagnostic repair for $2k so far and realize the value of these cars are rapidly falling.

Any insight, suggestions, or advice would be greatly appreciated. Thank you, Eric

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  #2  
Old 04-07-2009, 09:42 PM
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I would be more concerned that you are getting ripped off big time...that's what I'd be worried about.....the same mechanic? why go back to him?
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Old 04-07-2009, 09:49 PM
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Quote:
Originally Posted by cliffmac View Post
I would be more concerned that you are getting ripped off big time...that's what I'd be worried about.....the same mechanic? why go back to him?
I've been going to this mechanic for almost 5 years with no problems for general service/maintenace, so this is the first time I've doubted his abilbity.

Do you have a suggestion on what could be happening mechanically with the engine?
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Old 04-07-2009, 10:07 PM
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Did he replace the headbolts on the gasket change?
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Old 04-07-2009, 10:16 PM
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Did he replace the headbolts on the gasket change?
I will ask him. I'm assuming yes since the first headgasket lasted over 14 months. This problem happened suddenly and I can't belive he wouldn't have changed them. Thanks for the suggestion.
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Old 04-07-2009, 10:19 PM
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Well, ask yourself this question:

"If I knew the engine to be bad for sure, would I buy another one?"

If the answer is NO, then your best bet is to see if a new oil cooler will fix the issue. If it doesn't, I can't think of another reason other than head gasket failure or an internal crack in the block or head that would cause this problem (but that doesn't mean there isn't one).
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Old 04-07-2009, 10:20 PM
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I would also ask him how he tested the cooler...
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Old 04-07-2009, 10:22 PM
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One last thing - Don't be too hard on your mechanic. They're only human. If he's done good work and been honest to you so far, I wouldn't necessarily doubt him.

Every mechanic, even the best ones, have problems that leave them scratching their heads from time to time.
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1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition
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  #9  
Old 04-07-2009, 10:50 PM
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True, and something I often forget.

Quote:
Originally Posted by tinypanzer View Post
One last thing - Don't be too hard on your mechanic. They're only human. If he's done good work and been honest to you so far, I wouldn't necessarily doubt him.

Every mechanic, even the best ones, have problems that leave them scratching their heads from time to time.
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  #10  
Old 04-08-2009, 07:37 AM
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The mechaninc's steps were logical and good. The only question is if his test results are reliable. A cracked block is unusual, but so is a failed oil cooler ( with only 90K miles, and we know you were using the correct, corrosion-limitng cooolant). I think the cooler is more probable, though.
If you can pressurize the cooling system (not including the oil cooler), you should force coolant into the oil and determine if the leak is on the engine side. Ther's usually special equipment for that though. See example here
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  #11  
Old 04-08-2009, 08:09 AM
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Arthur D is CORRECT....have the oil cooler(heat exchanger) replaced.

There is an old bulletin on issues with those oil coolers allowing water into the oil!!!

Have replaced several on that model for that problem.
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  #12  
Old 04-08-2009, 06:26 PM
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oaklandw124, does any of this sound familiar??

Change the cooler.

M.B.DOC and I make 2 MB tech's telling you about the oil cooler bulletin.
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  #13  
Old 04-09-2009, 10:15 AM
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Quote:
Originally Posted by clarkz71 View Post
oaklandw124, does any of this sound familiar??

Change the cooler.

M.B.DOC and I make 2 MB tech's telling you about the oil cooler bulletin.
OK. Right now the shop that did the work has the manifold off and retested the cooler, saying it was fine. Should I have these guys replace the cooler or flatbed it to somebody else to do the work?
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  #14  
Old 04-09-2009, 10:21 AM
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You never answered Arthur's question - how did he test the cooler?
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  #15  
Old 04-09-2009, 11:45 AM
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Simply request them to replace the cooler! You are paying the BILL! Ask them to save the old one!

Most likely a small crack opens up under HEAT & Pressure conditions.

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