Step 1. Remove the cap from the radiator and inspect the pressure seal. If it has a dam- aged surface or has stretched so that t overlaps its seating, fit a new cap.

2. Gently liftthe vacuum seal in the centre of the pressure seal and make the same checks on the sealing washer.

3. Caps are usually stamped with their spring pressure on the top. This should agree with the maker’s recommendation (a dealer will know). If you suspect that the pressure spring is weak, a garage can check it.