I'm loosing a tank of coolant in one hit approx every month. I'll get in the car and have an alarm warning me that the tank is empty. This has been going on now for about 6 months but the car drives fine with no low level alarms until the following day when the tank is empty. I've been keeping an eye on the level before and after every trip with no drop in level, then all of a sudden the following day it will have lost a whole tank.
There's evidence that it's coming out from the cap, which has been replaced along with the tank.
The heating has also become very poor (worse on the drivers side for some strange reason) so I removed the heater matrix expecting it to be blocked but that was free flowing with no leaks.
Any ideas if the system can over pressurise itself and vent coolant through the expansion tank cap when the engine is switched off?
I'm at a loss now and can imagine that if I take it in to a garage they won't find anything due to the sporadic nature of the problem.