had a big service, my germam mechanic (old school)flushed the radiator 4 times to get rid of dirty water and add anti freeze. on driving home, the temperature gauge went up, and dropped on flat roads,the more hills, the more the temperature gauge went up, until it went very high. i stopped, let it cool down and checked the radiator, it was empty. my mechanic says its possible he flushed out some sort of sealant the previous owner may have added, along with a new radiator. the sealant maybe was to hide a bigger problem. he has said the head gasket is fine, but going to get head checked. i am worried it may be a cracked block,.have done 6000km since importing it from berlin, the temperature went up a little on a hill, but not much.would a special sealant last 6000km, i thought they were just for emergencies.he put a new thermostat in too. i noticed there was a tiny bit of grey or white smog out the exhaust that was never there before. i am baffled, just hope its not a cracked block. roger