hi, i have a problem with my heating, firstly the gauge in the car doesnt register when driving, only when sat still, and then it take ages to move, and secondly when driving the heaters are only ever warm, not hot, even after 30 mins driving, the expansion tank doesnt seem to hold much pressure either, it gets hot, but i can still unscrew cap and no steam etc...it doesnt use any oil or water, but i think mpg is down tho.....any ideas please?