Temp gauge on a 1992 GTI cabby

Hi any chance of a bit of help. Had my 1992 GTi cabby for just over a week and all is well, but noticed that the temp gauge only rises slowly to just above cold. When shes parked up with the engine running the gauge rises to mid way once on my way again it drops again. There appears to be no other issues I'm I right in assuming its the thermostat and if so how easy is it to replace. Its been hot today and when I turned my engine off the fans keep running for about 1 minute but most cars do that.
cheers in advance

yeh sounds like a stuck open thermostat to me,two ten ml bolts at underneath bottom of water pump to get access to change,just make sure you soak them in wd40 or similar as very to snap,as with the fan its meant to spin after shutdown only if it was hot enough to be on before shutdown