Posted on 6/27/2025
If you’re regularly topping off your BMW’s coolant but don’t see any signs of a leak under the car, it can be frustrating and confusing. Coolant loss without visible dripping is a common issue for many BMW models, especially those with higher mileage. The cause might not always be obvious, but it’s rarely something to ignore. Let’s look at the most likely reasons your BMW is losing coolant without showing clear signs of a leak and what you can do about it before it leads to bigger problems. Evaporation Through the Expansion Tank BMWs often use a pressurized expansion tank, which allows the coolant to move and expand as it heats. Over time, these tanks can develop hairline cracks or faulty caps that release small amounts of vapor. This doesn’t leave puddles, but the coolant level still drops. If the cap isn’t sealing tightly or the tank has a tiny fracture, you could lose coolant through evaporation. You might also notice a ... read more