BMW F10 coolant loss: most common causes
Why is the F10 losing coolant even though no leak is visible?
The cause may be an EGR cooler (exhaust gas recirculation cooler) leaking internally. The leak does not always show as smoke or a drip, and often an EGR fault code comes with it. The water flange under the intake manifold can also leak out of sight.
What causes the water flange leak and which part should be used?
The water flange on the engine head can crack or leak because the size of the aftermarket part does not always match. The leak has continued even with new aftermarket parts, and the original part has fixed the fault. The top bolt is under the intake manifold, so the replacement usually requires removing it.
Which other parts can leak coolant?
The water pump shaft seal can start to leak, in which case the fluid runs down through the engine undertray. A faulty thermostat, on the other hand, can overheat the engine. The pump and the thermostat are often replaced at the same time.