[Face15E]

Team, need some technical expertise I can't determine from the manual. Had the radiator replaced at the dealership this weekend. Upon pickup: Coolant full in right tank, zero visible in left tank (from a standing in front of the engine, looking from driver's side headlight back perspective).

I added a bit to the min line in the left tank, drove the car a few miles, let it cool and rechecked...appears empty. No warning lights etc. Advice?

Thanks,
Face

2017 Black 540i, 50k miles

[lnxguy]

If you're not getting the low coolant warning leave things as is..

[eric_gm]

Remember what's the function of the expansion tanks: As coolant heats up, it expands. Since a radiator can't grow in size to accommodate that extra volume, the hot coolant overflows to the expansion tanks. As coolant cools down, vacuum causes it to flow back into the radiator, so sometimes it's normal to find your expansion tanks low or empty. If the car is not throwing any codes for bad coolant level sensors or low level, you should be fine. Don't overthink it.

[Neusser]

Originally Posted by Face15E

Team, need some technical expertise I can't determine from the manual. Had the radiator replaced at the dealership this weekend. Upon pickup: Coolant full in right tank, zero visible in left tank (from a standing in front of the engine, looking from driver's side headlight back perspective).

I added a bit to the min line in the left tank, drove the car a few miles, let it cool and rechecked...appears empty. No warning lights etc. Advice?

Thanks,
Face

2017 Black 540i, 50k miles

Well if it appears empty, fill it to the max line. Drive for a few days and check.

[n-hampt4]

Tank should not be empty. The "left" or smaller tank is the low temp circuit tank, and does not have a sensor. It cools the turbo and charge air system. Top it off to full and check it. This system should not normally go low, as it's low temp, so does not experience as much natural loss as the high temp circuit.

Originally Posted by eric_gm

Remember what's the function of the expansion tanks: As coolant heats up, it expands. Since a radiator can't grow in size to accommodate that extra volume, the hot coolant overflows to the expansion tanks. As coolant cools down, vacuum causes it to flow back into the radiator, so sometimes it's normal to find your expansion tanks low or empty. If the car is not throwing any codes for bad coolant level sensors or low level, you should be fine. Don't overthink it.

You are describing an overflow tank system, very old school. Expansion tanks always have coolant in them.