backlash1

Hi
I've seen a number of expansion tanks leaking through the cap, either due to a faulty thread in the tank or the cap itself (the last one is more common). This kind of leak leaves none or little trace, but there's a way to tell. When the engine is hot, just before the thermostat opens and the fans kick in, you will see bubbles in your expansion tank, as the coolant boils due to the loss of pressure. Hope this helps. cheers
marc