Could the oil cooler be the reason I have gray sludge in the coolant reservoir instead of a head gasket problem on a 91 mercedes 300E if the dip stick shows NO milkiness and the car does NOT overheat and runs like a champ????

It may be the Radiator Transmission Cooler leaking ATF.
I note in EPC the radiator has been superseded twice.

The cylinder head gasket is common, and has been superseded several times, depending on engine number.

A Radiator Pressure Test and/or combustion leak test should confirm the issues.

Radiator Pressure Test 14pc Kit Color Coded Radiator Cap Water Tank Tester - Amazon.com

https://www.google.com/search?q=Lisle+75500+Combustion+Leak+Detector+for+Gas+and+Diesel+engines&rls=com.microsoft:en-us&ie=UTF-8&oe=UTF-8&startIndex=&startPage=1&rlz=#q=Lisle+75500+Combustion+Leak+Detector+for+Gas+and+Diesel+engines&hl=en&rls=com.microsoft:en-us&source=lnms&tbm=shop&sa=X&ei=rjQ-Ucb6Gofp0QGrjoHwCA&ved=0CAwQ_AUoAw&bav=on.2,or.&bvm=bv.43287494,d.dmQ&fp=14d62f9e067535c3&biw=1280&bih=823



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http://www.peachparts.com/shopforum/tech-help/237655-m103-oil-consumption-head-gasket-poll.html

http://www.peachparts.com/shopforum/tech-help/68627-head-gasket-valve-job-103-engine.html

http://www.peachparts.com/shopforum/tech-help/288624-what-brand-m103-head-gasket.html

http://www.peachparts.com/shopforum/tech-help/263890-m103-oil-coolant-leak-front-engine.html

http://www.peachparts.com/shopforum/2155238-post1.html


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__________________
ASE Master Mechanic
https://whunter.carrd.co/

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
2003 Volvo V70

https://www.boldegoist.com/

Respectfully disagree on the trans cooler, that sludge will be as pink as Pepto-Bismal, not grey.
Yes likely the head gasket, I never saw a blown headgasket blow coolant in to the oil, always oil in to the coolant, I don't know why. Be sure to replace or at least clean out the pressure tank as well as the expansion tank.

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I agree.
Thanks for clarifying that for him.

I only noted it:
* Alerting him to the multiple radiator super-session (issues).
* Because seriously burnt (carbon black) ATF has fooled me, both times the transmission was trashed.

Sadly I have seen engine oil in the coolant system more times than I want to remember.

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__________________
ASE Master Mechanic
https://whunter.carrd.co/

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
2003 Volvo V70

https://www.boldegoist.com/

Do you drive short or long distances?

If you only drive short distances it may be condensation, the engine has to be rather hot for a longer time to evaporate the water.

Rob

Rob, you're thinking of the sludge in the engine, under the oil cap, this sludge is in the coolant.

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Thsnks for your guys help. Im changing the head gasket next weekend

Make sure you have the head checked for flatness.

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