I have read a long discussions about the check valve between crossover pipe and radiator bleed pipe and which way it should be installed. There seems to be a lot of doubt if it was installed the “right way” in the factory. I have ordered a new valve EAC4168 and it looks like it is actually designed to be installed the way that check valve “ball” is facing the crossover pipe, as it will not fit the other way around. It looks like that Jaguar wanted it to work the same way as thermostat jiggle-pin. It should let the air out but stop the coolant flow when there is no more air. But apparently in real life it doesn’t work as intended and people have better experiance with check valve ball facing the radiator or without the check valve at all. In this case air and water can flow from the crossover pipe to bleed pipe but not the other way around. This setup made more sense to me as there will be constant flow from the crossover pipe to bleed pipe when engine is cold and should help to bleed the engine better when the engine is cold. When the engine is warm, thermostats are fully open and there is no coolant flow from the engine through crossover pipe to water pump, the check valve will prevent the coolant from being sucked by water pump the other way around. So I decided to modify the new check valve as per pictures below:
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I like it. I guess more of us are in agreement that this thing was installed by Jaguar the wrong way around. I should point out, though, that theoretically the suction is HIGHER in the air purge plumbing than it is in the crossover pipe, so coolant shouldn’t be pulled backwards anyway.
Suction is definitely HIGHER when thermostats open, but I’m not sure if it is still higher when thermostats close crossover pipe. The inlet to water pump from crossover pipe is always open so when thermostats close, the only flow that is available is bleed pipe so this is the question which is stronger, Venturi effect suction bleed pipe or water pump suction. I’m just speculating here 