Oil floating on top of the coolant in the radiator reservoir

ENEISHA LOGAN

MEMBER
2005 DODGE MAGNUM
2.7L
V6
2WD
AUTOMATIC
267,000 MILES

I have the SE model. I have recently noticed a little oil floating on top of my coolant in the radiator reservoir. I performed a block test and my head gaskets are good, no combustion gas going into my system. My car doesn’t have an oil cooler originally but it does have a transmission oil cooler attached to the radiator. No overheating and no oil leak a little sluggish in accelerating between 40-60 mph.

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

Hi Eneisha,

Did you perform the block test looking for combustion gases when it was hot? Also, I would suggest performing a cylinder leak down test. This will show if there is anything leaking from the combustion. The block tester is good but a cylinder leakage is very definitive.

Also, if there is not a lot of oil I would suck out the coolant and oil from the reservoir so that there is no more oil and then top it off. See how long it takes to come back. If it is relatively quick then it would be needed to get more aggressive. If it takes a while then I would just keep an eye on it and not worry about it right now.

As for what it could be, most likely it is a head gasket that is just starting to leak. The cylinder leakage test should show this but if it were an oil cooler, you would find oil in the coolant but also coolant in the oil. Have you checked your oil to see if there is any coolant in either the trans or engine? You are correct that you don't have an engine oil cooler but it is still worth checking.

As for the sluggish feeling, that could possibly be a loss of compression but on its face, I would not think it is related to a small amount of oil in the coolant.

Feel free to take a picture of the amount of oil and sending it over and I can see what you are seeing. Thanks

https://www.2carpros.com/articles/head-gasket-blown-test

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