I have a 2002 1.8 Astra Coupe engine Z18XE .
It does not seem to be getting up to temperature . If i take it on a long run it will go just below 80 on the temperature guage for a very short time if driven fairly hard ,which I have done soley to see if I could get the guage to move , then when I return to driving it normally it soon drops back to virtually zero normally sits at the second line at the start of the guage.
I suspect it's the thermostat but the heater seems to be working normally if the thermostat was stuck open would the heater still work as well as it seems to be doing.
Also I topped up the coolant a while ago and just put in pure coolant which I didnt mix with any water ,would this cause my problems