Accidentally put engine oil in coolant reservoir 325xi bm...

Q: Accidentally put engine oil in coolant reservoir

asked by on June 14, 2016

Accidentally, because I was in a hurry, I put engine oil into the coolant reservoir. I went round trip out-of-town, about 600 miles. After returning home and washing my car, I washed under the hood and that’s when I realized my mistake. I immediately got all the oil and coolant from the reservoir. Should I drain the whole coolant reservoir and/or replace it? Thanks.

The coolant reservoir on your particular vehicle is a part of the pressurized system. In this case, the oil that was in the cooling system can cause a few different problems. When oil and coolant mix, they turn into a sludge like substance that can clog lines and get stuck all throughout the system. The water pump can fail due to the sludge and the various o-rings and seals can fail in the cooling system due to the oil. This problem is more serious than just draining the coolant as the whole system is contaminated with oil, which must all be removed at this point. A qualified technician, such as one from YourMechanic, will be able to asses the situation and flush your radiator fluid if necessary.

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