Check the thermostatic spring of the valve to make sure it is hooked up on the stop pin. The spring stop is at the top of the valve housing when the valve is properly installed.
Make sure the spring holds the valve closed. Actuate the counterweight by hand to make sure it moves freely through approximately 90° of rotation without binding.
The valve is closed when the engine is cold. However, a properly operating valve will open when very light finger pressure is applied to the counterweight. Rapidly accelerate the engine to make sure the valve momentarily opens. The valve is designed to open when the engine is at normal operating temperature and is operated at high rpm.
Lubricate and free the value with the non-flammable solvent if the valve is sluggish or stuck.