My 1991 MB 300E has ATF oil in the coolant resevoir. Found a brown layer of oil floating on top, checked my engine oil level, no change, checked my ATF and it was dangerously low.

Anyone know what's going on here, and what type of repair bill i'm looking at?

P.S. There were no signs of coolant in the tranny fluid.

Thanks in advance

I think that is a rare symptom of head gasket failure. Has it even been replaced? Do a search (at top of the page), and you should come up with some information. Good luck.

Not if it is an ATF leak David.
 

If the motor oil level is unchanged but the ATF level is low, sounds like the tranny cooler in the radiator may have sprung a leak. This is something you need to remedy ASAP as anything other than ATF in your tranny will result in an expensive repair bill. You can pull the radiator and have it pressure checked (both coolant and tranny cooler sections). This may not be repairable (not sure due to the plastics) and you may just have to get a new radiator.

The ATF heat exchanger in the radiator is leaking. You will end up with coolant contamination of the transmission as it gets worse. With the engine running the mean pressure of the trans oil is higher that the cooling system pressure. But, when the pump in the trans is not producing pressure and the engine is still hot from recent running, the pressure gradient will change and you will get coolant entering the ATF cooling loop. Replace the radiator ASAP. You do not want water or ethylene glycol in your transmission..

I know that it was ATF... I *thought* I recalled that being a rare symptom of head gasket failure. I guess not... sorry about that.

So you're saying there are two sections of my radiator? One to cool engine and an ATF cooling section, that has apparently failed?

Besides the tranny fluid in the coolant, after a semi-long to long drive pressure from somewhere is pushing coolant out the overflow hose and onto the ground just behind the right front wheel. I assume this pressure is coming from the transmission?

Thanks again for your expertise~~!

Iodyn

Check your tranny fluid fast!
 

If there is ATF in the coolant, there is a chance that there is coolant in the ATF. This will do a number on your tranny is there is enough of it. I would drain the tranny and take a look. Better yet, after you change out the radiator, drain the tranny and treat it to a new filter & gasket.

I would also check the head gasket out, maybe a compression test/leakdown.

Just my humble opinions. Good luck!

Over flow Tank
 

Brother of The Benz, iodyn
The liquid leaking from under or the area of the right front wheel is from the overflow tank.
The combination of oil and coolant will continuiously be exchanged with coolant in the radiator tank.
It isn't normal for this tank to over flow, it's from the radiator being over filled or excesive pressure in the radiator and the coolant being discharged as the pressure cap vents.
You should clean the overflow tank, it is gained access by removing the r/f wheel and the inspection panel under the fender.
With any age on your Benz, this would be the time to replace the over flow hose.
Get the radiator replaced or repaired.
Don't overlook the transmission fluid to radiator hoses. There are two of them.
Change the transmission fluid and the engine coolant.
There is an excellent article in the recent MBCA Star Magazine on M/B engine cooling. Read it and enjoy.
Happy Trails Beep Beep from The Spiderman in Houston!!!

Iodyn,
Just yesterday got my car back from the shop. Had brown fluid in the coolant tank, thought it was oil, but now think it was ATF since just last week the plastic side tank of my radiator sprung a BIG leak while idling in my driveway, spewing coolant everywhere. The lower 1/5th of the 124 radiator is a transmission cooler, so if there is deterioration it is possible for ATF and coolant to intermingle. Seems the radiators in 124s, at least, are almost considered a normal wear item. Even with a reinforced neck (which mine had), the plastic tanks on each side seem to get brittle with age (and I have always used MB coolant). (Mine has 99K miles on it.)


On another list I recall reading that some recommend prophylactically replacing radiators on some models at 100,000 miles. Now I know why. Just glad mine didn't go kerflooey on I-80 in 95 degree heat.

I thought all that is inside a radiator is coolant, im amazed that the ATF is actually going into the radiator.

Can somebody explain in more detail abt this? i was under the impression that the tranny is cooled by coolant, ie like the engine block.

what abt other mnakes and models? do they work the same way?

is there such a part to replace the plastic part of the radiator? my friend toyota radiator just sprung a leak and he manage to get the plastic part replace at a fraction of the cost of a new radiator. Can this be done for the w124 then?

Quite Simple angbrian
 

Brother of The Benz, angbrian
Your W124 radiator has it's fluid tanks vertical on each side of the radiator assembly.
In the passenger's side tank there are cooling coils. There are two lines attached to fittings on the tank.
Transmission fluid circulates through the cooling coils and the fluids heat is removed by the engine coolant.
Have a look see!
Happy Trails Beep Beep from The Spiderman in Houston!!!

Consider Deoiling the cooling system after you install the new/repaired radiator. Phillip (PrtsShop) has the MB part number for it as I recently asked him about availability, and seriously consider going MB coolant.

Happy Trails

Thanks immensely for all the help everyone. I truly appreciate it. I'm simply glad to know that it's most likely limited to radiator replacement, instead of something more expensive.

Also, about that part JR Brown, is this some sort of system flush that you speak of? Like a citric acid of sorts that dissolves the oil in the cooling system and flushes it out?

Thanks again!

Orange or Lemon/Lime?
 

Brother of The Benz, iodyn
You can have it with your breakfast or mix it in your filled radiator.
The Citrus Radiator Cleaner from M/B is P/N 000 989 10 25 for a 0.5kg pack.
I change the M/B Coolant every year(30%) and I've used the cleaner every year.
My 1987 300E has 177,000 miles and I'm still on the original radiator.
I've replaced the upper and lower radiator hoses one time and none of the other under the hood hoses.
Says something for the cleaning ability.
Give it a try.
Happy Trails Beep Beep from The Spiderman in Houston!!!

Change dat raditor quick ,then go to lube place that dose transmissiom back flush ,about $80.00 out here (Oregon) beats taking a chance on a tranny rebuild.....
William Rogers........