EMan 928

Hi everyone,

I know that is not a MB forum, but I'm hoping someone here might be have had some experience with this car and can shed some light. My daily driver is a 1992 Mercedes 300SE. It has an inline 6 cylinder engine (The M104) with 91,000 miles that has a mysterious problem, according to my mechanic. Two weeks ago I found oil in my coolant reservoir and the oil in my engine was down about 2 quarts. There was no coolant in the engine oil (no milkshake consistency)on the dipstick, but the coolant in the coolant reservoir had the milkshake consistency. I called my mechanic who suspected it was a head gasket. I was disappointed because he had done the headgasket 13 months earlier. So, he went ahead and replaced the head gasket and he tested the oil cooler. He then called me and told me after putting the engine back together and flushing out the system, he is getting the same issue...oil is somehow entering the coolant and the engine oil level on the dipstick is showing about 2 quarts less. He is baffled. The engine has been running fine, no overheating. my mechanic suspects that something suddenly happened to either the cylinder head or the engine block and is hesitant to tear the engine down again to try and chase a bad cylinder head. The oil cooler is serparate from the radiator (it's near the oil filter housing) and I asked him if he tested the oil cooler correctly and he said he had.

So, I had the car towed to the local MB dealer for a second opinion. They also ran the car for about two hours and noticed the same thing - oil is finding its way into the coolant and the oil level in the crankcase is going down. They are suggesting the previous mechanic did the head gasket incorrectly. They want 4k to redo the gasket and replace radiator, hoses, etc that had oil in them. OUCH!

So, I have a engine that is somehow injecting oil into the coolant system, but the oil in the crankcase is clean (no milkshake consisitency). Do I assume that the tests on the oil cooler were not sufficient enough to reveal a faulty oil cooler and I should just go ahead and replace the cooler with a new one, or do you guys think the engine somehow has a failed block (waterjacket) or cracked/warped cylinder head? Most everyone I've spoken with says that the blocks and heads of the MB engines are so strong that it would be hard to assume that happening. And, my car has never overheated. Any advice/recommendations would be greatly appreciated.

Thanks,

Bill51sdr

Might want to try the OT forum as well with this as well.

dprantl

There aren't that many other places coolant and oil come close to each other. If it really is not the oil cooler, it must be somewhere in the head. The reason you are seeing a milkshake only in the coolant system is probably because the oil pressure is much much higher than coolant pressure, so that's the direction it flows through the leak. By chance, does this motor have a oil condensing hose? It's a system where an inner hose runs coolant and an outer hose has oil vapors. The idea is that the coolant condenses the oil vapors and the resulting condensed oil is drained back into the pan. However, that would show coolant in the oil pan, but still something to check.

Dan
'91 928GT S/C 475hp/460lb.ft

EMan 928

Hey Sterling,

He said he checked for warpage using a flat edge blade and cleaned it up but he did not have it milled. The first time he did it 13 months ago was primarily preventive maintenance...there was a small leak on the outside of the engine block but no oil in the coolant. I'm hesitant to rip the mechanic...he's been in business since 1975 and has worked on my car for the last 5 years. Plus, he says he's done a bunch of these headgaskets. The only thing I can think of (other than a cracked block/head) is that oil cooler. Maybe it has failed internally and somehow still passed his testing.

Mrmerlin

a clue from the dealer they want to replace the radiator??
does the MB have a similar coolant/oil exchanger, if so then maybe it has sprung a leak.
So what is happening is that oil is getting into the coolant and not the other way around.
At any rate your gonna be into replacing all of the rubber coolant lines as once they are exposed to opil they will lose their strength and split or slide off the connections

EMan 928

Correct, oil is getting to the coolant reservoir tank, but the oil in the crankcase (by looking at it on the dipstick), is still clean. I know I'll have to replace the hoses and other items that the oil has contaminated. But right now I'm trying to figure out if the engine or head is cracked or if it is still salvageable.

Lizard928

There is one massive clue here,
That is that you are getting oil in the coolant, but not visa versa.
Considering that the coolant system runs at pressure it should normally be the other way around.
This means that where they are joining/crossing over MUST be a high pressure oil zone.
So either if the cooler is in the rad, or where the head mates to the block. The oil supply to the head might have a small nick that is simply preventing a proper seal.

The reason MB wants to replace everything is because it is a pain to clean it all out 100% and there may be small cracks causing the problem there too.

But I believe if you study the oil system carefully on the high pressure areas you will find there are limited spots for what I am suggesting and to track it that way.

mark kibort

I never understood how oil can get in the coolant. remember, even though oil pressure is higher at the pump, its not so in the pan, or in the heads, or is it. are the lines still under pressure, until they hit the cam bearings and leak out? If so, i guess thats how it gets in the oil. water in the oil, under only 1bar pressure could happen if the water pressure got to high during overheating and leaked into the oil passages through the head gasket, right? I can certainly understand oil in the water if there is some leak at the side oil cooler tanks on the radiator. my only experience with head gasket leaks was air from the combustion chamber entering into the water jacket and overpressurizing that system, or pushing water into the center valley out of the head gasket.

blown 87

Was a chemical test for hydrocarbons done to the cooling system to check for head gasket leaks?

You say you replaced the oil cooler?

How was the machine work done? surface mill, was it baked and twisted?

I have seen this on a few MB's sometimes it is just the cooler, but when I do a head gasket, it always gets a new cooler.

This is just what I think has happened, who ever did the machine work (if it was done at all) used a belt to surface the head, or some other mistake was made when doing the head.

Most times on a MB when it loses a head gasket, it will put oil in the coolant, but not in the oil.

Just from what I have seen on them.

blown 87

Mark, in the last 16 years, I have only seen one MB put coolant in the oil.

We have done maybe 60-70 of MB head gaskets in the last 15 years, never had one come back, thank goodness.

Bill51sdr

Kind of a moot point as there are in fact HC's in the coolant; oil .

Sure does sound like the oil cooler is leaking into the cooling system though.

blown 87

I do not think oil alone will make the solution change color, it is the Combustion gasses the make it change color.
I guess I should have not said hydrocarbons, because you are right, that is what oil is.

Bill51sdr

I used to check suspected blown head gaskets with a 4 gas analyzer we had on hand. Get the car warmed up and hold the tip over the radiator or coolant reservoir opening (quick reflexes were necessary for the occasional sudden boilover ). It was a pretty foolproof way of detecting combustion gasses where they shouldn't be.

blown 87

I have used mine also for that, but I just take the cap off.

I bet I have not turned my four gas on in 2 years, but I got a new O2 sensor for it this week, a member here wanted to use it to set his CO.

EMan 928

Oil cooler hasn't been replaced yet. Both the independent mechanic and now the MB dealer said it isnt the cooler. Dealer did what he called a "flow test" to determine it was functioning normally. But, it is the only thing that hasnt been replaced. Maybe both are wrong.