How interesting, SO the rectangular box on the passenger side of the oil pan is an oil cooler?

my silver 95 had a small leak from one of those metal tubes that come from that " oil cooler"

It sounds awful that oil was/is getting into your coolant. I would have immediately thought blown head/headgasket. This is good info to know.

My oil leak isn't from the oil cooler, it's from the actual oil pan. *I will have to take a picture tomorrow* It's hard to explain but a picture is worth a thousand words.

It's actually a "heat exchanger." When the engine is started from cold, the coolant warms up first. The heat exchanger transfers heat from the coolant to the oil, helping it up to operating temperature. That's good for the engine. Later in your drive, when the oil is hot because you've been pushing a little, the heat exchanger transfers heat from the oil to the coolant and the radiator transfers the heat to the airflow. The NA 606 is relatively unstressed so that method works. The later turbo 606 went back to an oil-to-air cooler because there is just too much heat to get rid of.

There are several oil seals (o-rings) in the heat exchanger that can leak—mine did. The oil pan itself has a gasket but changing that is non-trivial because the engine has to be lifted to get the pan off.

Jeremy

Thank you very much for the info, Jeremy! I finally took the belly pans off today and intend to leave them off until this is sorted out. I noticed as you said, oil was leaking from the heat exchanger, Wiped it, and it re appeared.

I tried tightening some of the oil pan bolts, and the heat exchanger bolts which were pretty loose and I've driven the car around for about 30-45 minutes since and haven't seen any additional oil leaks..

I am not calling it a success yet as they leaks may reappear! but so far so good.

If this does fix the problem, it's pretty interesting as I have work orders from the previous owner who took it to a mechanic who couldn't find the source of the leak.

FYI the pictures are before I tightened any bolts. Degreasing the engine made these oil leaks very easy to see. I just hope the previous owner was mindful and never ran this car low on oil!

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Tightening the bolts may very well help. I did some of that myself. If not, the heat exchanger o-rings are not expensive or difficult to change.

Thank you for the info! I really appreciate it!

I will definitely change the heat exchanger O ring when I do an oil and filter change. hopefully the pan gasket will not leak anymore because I really don't want to change it... at all.. I had to do a rear main seal in my truck (72 c20 350 V8), and did the oil pan gasket while I was at it, Jacking up the engine and crawling underneath the truck was not a lot of fun.

The mercedes looks to have less available space.. it doesn't look fun. haha.

So do you get the heat exhanger O ring at mercedes?

Good info, an insight as to the possible slow oil leak on my moms 95 e300.
Thanks guys, always good to armed with a bit of knowledge before tearing into things

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97 e300d, 78 300Dt, 95 E300d, 94 E320 estate

Also check the oil level sensor on the side of the pan as well.

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UK spec Mercedes W210 E300 Turbodiesel wagon - OM606.962 with 722.6 transmission - rust free!

It's probably easier to get the heat exchanger o-ring from a dealer—only a few dollars.

The oil level switch on the other side of the pan also has an o-ring that can leak. Might be worth changing it too while the pan is empty and you're underneath. Again the o-ring is not expensive.

Take opportunities like this to wipe clean anything you can easily reach. It makes future jobs easier and cleaner and future leaks easier to spot. Another advantage of doing your own work—cleaning is something a hired mechanic does not do.

I noted that it wasn't really leaking when I drive the car, but park it a day or so and then the oil leaks

I went to mercedes of fairfield, really nice place.
Eeesh 30 bucks for the 1 large O ring and 2 small ones.

I changed them out today, it went well, aside from getting an oil shower from residual oil in the cooler, and then getting rinse off with coolant

Lol It will all be worth it if it doesn't leak anymore

Hi, I have the same problem with my 95 E300 diesel oil/coolant heat exchanger slowly leaking oil and I want to change out the seals, or o-rings. Does anyone have the MB part numbers for these o-rings? Thanks! Alex.