Guide: Replacing Thermostat
 

Engines: 1.6/1.8/2.0 Petrol

Symptoms: Poor MPG, Low engine temp, poor heat output on heater.

Time required: 15 Mins

Tools required: Torx driver (sorry forget what size..)

NOTE: Ensure engine is cool before attempting or risk of scalding.

Engine temp should be around 90°C anything below this indicates a fault. My car was running at 78°C, I have seen some worse and some better. For a while mine ran at 85°C and I didn't believe the thermostat to be at fault. I was wrong, 960KG was right (I'm going way back here..).

Follow top radiator hose to locate thermostat cover and remove the 2 torx bolts (you will lose about a cup full of coolant):
http://i102.photobucket.com/albums/m...-Muove/1-1.jpg


Move hose out of the way:
http://i102.photobucket.com/albums/m...-Muove/2-1.jpg


Remove old thermostat:
http://i102.photobucket.com/albums/m...-Muove/3-1.jpg


Ensure new thermostat is correct and ensure it comes with O ring:
http://i102.photobucket.com/albums/m...-Muove/4-1.jpg


Fit new o-ring onto new thermostat:
http://i102.photobucket.com/albums/m...-Muove/5-1.jpg


Install new thermostat:
http://i102.photobucket.com/albums/m...-Muove/6-1.jpg


Retighten thermostat cover torx bolts:
http://i102.photobucket.com/albums/m...-Muove/7-1.jpg

Top up any lost coolant. Coming into Spring summer I just topped up with distilled water. Any other time I'd replace coolant.

Job Done :) Put kettle on.

Maximum temp car achieved on tickover with old thermostat:
http://i102.photobucket.com/albums/m...-Muove/8-1.jpg

Maximum temp car achieved on tickover with new thermostat:
http://i102.photobucket.com/albums/m...Si-Muove/9.jpg

The difference is significant! I haven't been for a drive yet, but I bet the MPG is improved massively! I have to do a 200km drive to Helsinki on Thursday, a good MPG test. With faulty thermostat I got around 37 MPG on motorway runs, I will report back Thursdays finding and see, once and for all just how much a thermostat affects MPG.


Edit: Original thread