Took the Z3 in for the MOT today. The good news is, it passed the emissions test (I asked them to do this first as it failed last time and I replaced the cat) The bad news is for some reason the pressure in the rad built up while on test and blew a sizeable chunk of the rad filler tank out. I couldn't believe it as I'd taken the car for a 12 mile drive prior to taking it to the test centre and the car was fine. I'm now puzzled. Why would this happen during the test as the emissions test where the car is deliberately revved up had already been done? Should the filler cap have let the pressure down? (Does it work this way or is there another pressure relief valve somewhere?) Does this build up of pressure indicate problems with the pump or thermostat or headgasket? I've seen an ad for a Z3 filler tank only. I didn't realise these could be replaced. How do you couple up to the honeycomb and make a watertight seal? Again sorry for asking such questions but I really thought the car would pass the test this time.