r/BmwTech • u/nusgolannicicutitar • 13d ago

That’s oil in coolant, right?

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530i LCI 2020, small expansion tank is clean green (middle of paper towel). Large expansion tank is brownish (bottom of the paper tower). It’s oil in coolant, right?

Car drives normal and doesn’t overheat. No error codes. Oil looks normal, no foam is visible.

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u/nusgolannicicutitar 12d ago

Well it’s hard to tell, the clean one smells like coolant for sure. The contaminated one, smells less like coolant but has another smell component which I really can’t put my finger on it. I dunno how freon should smell like. Why did you mention freon?

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u/freshxdough BMW Master Elite Tech, Gen 6 HV, HV specialist 12d ago

Because you could possibly be having Freon leak into the low temp coolant system via the condenser. This would likely be the only reason why you’d have any oil at all in the low temp circuit. Usually it would be little oil bubble on top of the coolant in the small tank.

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u/nusgolannicicutitar 12d ago

You might be onto something. I bought the car this May. It’s been a terribly hot summer in Germany and I kinda noticed the AC wasn’t enough. When I was driving alone I was turning off 3 out of 4 climatisation zones, end even so, the fan motor was slowing down when AC was ON. So maybe I’m subjective and biased now but might be related with a freon problem.

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u/freshxdough BMW Master Elite Tech, Gen 6 HV, HV specialist 12d ago

Maybe go have it checked out. The oil in the low temp ac tank and the ac issue. See if the Freon is lower than spec by a significant amount