How long can oil stay in the cooling system? - PeachParts Mercedes-Benz Forum

JohnM. · #1 10-08-2012, 03:38 PM

OK. So I did my head gasket 90,000 miles ago. Before I replaced the HG, the cooling system was basically peanut butter filled (coolant + oil). It took about 2 years of wiping under the expansion cap to get all the oil out.

Last week I noticed a small amount of oil in my expansion tank. What are the odds that this was a bit of oil from before I did the head gasket? I just started using the heat recently, maybe it was lodged in the heater core? Maybe that's just wishful thinking.....

Hoping it's not the HG, because it will force me to make major performance upgrades I'm not ready to make yet (turbos)...lol

oldsinner111 · #2 10-08-2012, 03:49 PM

I watched a show saturday they advertised layered head gaskets.Better than stock.Better materials,and perfect for forced induction.Old oil won't hurt as a matter of fact I have used a pint of oil to help noisey water pumps.

MEPEH · #3 10-08-2012, 04:03 PM

Chances that it came from the heater core are pretty low.
As far as i remember the water circulates through the core even when the heater is set for full cold. So the bigger circulation helps with cooling the engine.
It's the flap that changes from cool intake / heat intake

JohnM. · #4 10-08-2012, 05:00 PM

I'm going to keep an eye on it for now. I'd also find it hard to believe that its old oil contamination from nearly 5 years ago / 100K.

Not happy. Just put a tonnn of work into suspension/brakes/belt system. ARGH.

MEPEH · #5 10-08-2012, 06:12 PM

I know the gasket leaks in different spots. But i would open the coolant reservoir and check for bubbles with the running COLD engine. Also, pull the oil dipstick and check for coolant contamination there. If those 2 check ok, than you have more piece of mind.

While you are there. Remember the coolant level, or mark it on the reservoir for future reference

JohnM. · #6 10-08-2012, 11:30 PM

No bubbles, no coolant in the oil.

I am loosing a small amount of coolant due to a aux. water/heater pump that is bursting at the seams. We are only talking about a few drops worth of oil in the coolant though. Some of the oil I fished out of the expansion tank today looked RATHER old, it was gray-ish in color.

Maybe some oil residue was released from the internals of that aux heater pump as its failing more? Quite possibly the worst time for a HG replacement right now in life, so I gotta exhaust all the possibilities

The aux heater pump just started leaking more recently.....

I guess I need to do a compression / leak down test. *sigh*