Expert: Sean Halliday - 12/26/2008

Question
Hi Sean.  I have a 2001 VW Jetta GLS 1.8L with ~83K miles.  Recently I noticed that my temperature guage is not coming up to operating temperature (maybe 1/2 way of normal operation) even after several hours of driving.  The car appears to be running just fine but the guage is not reading correctly.  I am thinking it is either a faulty temperature sending unit or thermostat stuck open.  Do you happen to know how to check for a properly functioning thermostat without removing it from the engine?  I found the thermostat and it looks like it will be a bear to remove so I would rather not if possible.  Would you be able to provide some direction how to test the thermostat or do you think it could be something else?  Thanks for your advice.
Andrew

Answer
With the outside temp a lot cooler,the engine will not heat to where it usually does.My own car does exactly the same thing.Temp is half normal.(Outside temp is 55 degrees).The thermostat works if the heater works ok.As normal, that is when you start the car and the heater warms up and is hot after 10 mins or so.If the heater doesnt get hot or blows cool,then it could be stuck open.