Possible thermostat Issue?

[dave192]

I'm looking for some advice please. I have a 07 plate sport back and over the summer we were going though coolant at a fast rate, the reservoir would be empty. sometimes when the cap was taken off the reservoir would fill and other times it would not. I did the following to try and address the issue:

1. Used BAR seal to see if there was any leeks

2. Tried releasing any air locks

Problem still persisted through summer, but know the colder weather is setting in we rarely getting the warning on the dash and have only had to put coolant in twice since August, but now have a problem with the heating. It can sometimes take over 7 miles (school run is 7 miles one way) for the heating to kick in.

The engine runs at 90 all of the time, I am thinking the Thermostat is at fault.

Any thoughts would be great

[Geraldy212]

HI Dave. First of all, you seem to have a coolant leak. This is a closed system, with NO loss of coolant at all, if the coolant circuit is properly secured. Suggest you check the radiator (in the corners) for leaks. Well known problem. Have the undertray off, run the engine until hot and look for leaks. Other possibilities are the water pump and the cylinder head. Both need attention to make sure they are not the culprit. A pressure test should be done to see where the coolant is going. Now, if the engine is running at 90 deg, then the thermostat is doing its job. If the thermostat is jammed open, the temperature would be lower, and if the thermostat is jammed closed, then a higher temperature would be seen. It seems that the heater matrix is not receiving hot coolant, or the heater flaps are in the wrong position. A VCDS error scan may help to pinpoint where the problem is. Heater flap positions can be reset using VCDS. Bear in mind that if you have a diesel, they do take a long time to warm up. Just some early thoughts. Good luck.