x2 on using genuine thermostat as well.

I was in a rush and bought a Repco one before a trip and it played up big time. Sometimes jammed and didn't open and they also opened up at 80 degrees rather then the standard 76.5 on a GQ TD42 and I had a lot of overheating issues. Never had that with the original thermostat so go the genuine!

Also with a thermostat stuck open or not having one can cause problems with your engine not reaching It's ideal running temp too.