300E 91 150K Mi light brown oily liquid floating in coolant tank
 

Engine is running perfectly with stable, normal idle.
No emulsion visible on oil dipstick, only engine oil, dark brown.
Transmission dipstick shows very clean light brown oil.
Flushed coolant with water hose open in coolant tank, engine running, letting water out through open radiator valve at bottom: some tan colored sticky liquid came out through the bottom, then stopped. After 15 minutes more flushing, closed the radiator drain valve and used the car again...next day: some of the same light tan colored liquid was collecting on top of the coolant in the coolant tank...
Can this oil come from the transmission radiator built inside the coolant radiator, and if so, how can I check for this?
Or can it still be the head gasket failing, even though the engine runs fine and there is no sign of water on the oil dipstick? If so, is there a test I can run to help narrow it down to this problem?
THKS.

My guess is that the head gasket is leaking oil into the cooling system. It is a pretty common failure point on the M103 engine. Do you know if the gasket has ever been changed? I find it strange that the oil dipstick does not show contamination of engine coolant. Have you checked under the oil cap for contamination?

Trans fluid is red. Sounds like head gasket. : (

The oil generally leaks into the cooling system on the 103 because of the design and pressure. As said above, transmission fluid is red, not brown. If it is oil, you'll need to get a head gasket job done asap. If you are handy and inclined to DIY, search my name for my rebuild thread. You may want to get a compression test done...it should indicate it.

From the description, I'd be pretty certain it's the head gasket. A very doable DIY on these if you like to work on cars.
Usually you don't have to park the car immediately, but if the amount of oil showing up in the tank dramatically increases or it starts running hot or overheating you'll need to park it and get it done (syphon off the oil floating in the tank every day or two).
Unless you just don't want to chance it at all, you'll probably be able to drive it until you can make arrangements to fix it.

103
 

The above is very correct advise .
i was able to drive for a couple of months just the way it was, nothing disastrous happened.
mak
300SE

That tranny fluid should be red, brown means it's old. New fluid & filter time.


If it's brown, flush it down.:D

Transmission fluid SHOULD be red. However, if it's the same color as the stuff that's coming out of your radiator, it's *possible* that the fluid cooler in the radiator has ruptured.

Change your tranny fluid (it's old anyway). If what comes out of your radiator turns from light brown to red, then there's your culprit.

Thanks to all of you for your very valuable responses!
I have checked under the oil cap and saw nothing like a cross contination sign.
It sounds like I do have a little time to drive it like this from yr input
head gasket was replaced @ 60k
radiator was replaced @ 63k 84k 136k 3 times!
I will do a compression test this weekend
and also check radiator, drain oil and trans oil to see what else I can find
let me know of any more ideas or advice
thks!

There's nothing else that would cause oil in the coolant tank other than a leaking head gasket. You can have no coolant contamination in the oil and have oil in the coolant.

I ran my car for about 500-1000 miles when it was just starting to get oil in the coolant. It ran perfect. But soon my coolant turned into a nice peanut buttery sludge. After I did the head gasket. It took 15K miles, a new radiator,new coolant tank, 3 coolant flushes, and constant cleaning of the coolant cap to get rid of the oil contamination completely. Don't let it get too bad by driving it, or you will pay the price down the line!

Papatatun, it would be best to diagnose the problem and repair immediately. As John M. points out, procrastination will only make things worse and possibly more expensive to repair.