[Dominik]

I once had a slowly overheating engine. Always a bit low on coolant, but blamed it on heat, pressure cap, phase of the moon...

Tested all you did, only to be unable to crank it after winter storage one year. Took the plugs out, one was rusted and the cylinder full of water.

I had a leak in one intake seat. Just that winter this valve happened to be open and let water seep into the cylinder.

Looking back, this must have been the most untraceable water leak I ever had.