the car ('99 1.4 16v sport) has been losing water from somewhere, and been missfiring on i think one cylinder. this morning it missfired as usual, but when i turned on the heater it was not blowing any hot air whatsoever, just cold air.
then i shat myself and looked at the water temp guage and it was reading maximum!!!
so i pulled over and checked there was plenty of water in the header, but it was showing empty (although when i realeased the presure the water rose back into the header tank,is this normal? )
also the engine didnt seem overly hot,it had been running for about 10 mins

started it back up and the temp semmed to go down and it ocassionally blew some hot air thru heaters.

is the thermostat to blame for this or is it the water pump,

i need help,please,
dont want to warp my head, and 10 petrol has done 32 miles!!