Usually a bad seal will begin by leaking when the engine is close to body temperature (yours) and before the pressure gets behind it and helps it seal better. As the temp increases and the pressure builds it presses the seal tighter and stops the leak (until the car cools through zero pressure again).

When they finally let go, it will leak all of teh time.

Bob

Hello, I have an 86 bmw e28 and it is leaking between the block and the waterpump but doesn't do it all the time. It leaked constantly about two weeks ago for about a week and is not leaking anymore, was it just to hot or what? Thank you