Step 1. Remove the thermostat . Hold the flange with pliers and submerge it in a pan of boiling water. The valve should open within approxi- mately 30 seconds. When fully open the thermostat valve will be about~in from its seating.

2. To refit, scrape clean the seating on the cylinder head. Some thermostats are marked with the word radiator’ or rad’ on the flange. This marking goes nearest to the radiator.

3. Fit a new gasket after the thermostat, smear with high- melting-point grease, replace the cover and tighten the fixings evenly.