1. The valve should open fully at a coolant temperature of 20°C and close when it rises to 70°C.
2. To check the valve on a cold engine, remove the valve box and blow into it: air should pass. If not, then the valve is faulty.
3. To check the valve on a warm engine, start the engine and let it run, at idle, pinch the hose between the valve and the manifold. The engine speed should not change. A change in the crankshaft speed indicates a jamming of the control plunger and the need to replace the valve.
4. To replace the valve, drain the coolant, disconnect the cooling system hoses and remove the valve.
5. When installing a new valve, replace the seal.