isuzufool wrote:It is really a useless valve and can be eliminated from your system. It was originally designed to up the idle speed if the engine gets too hot to pull more air through the radiator I think, but that is stupid anyway. The later model 2.6L engines did not use them at all, nor did they have the air induction pump for the exhaust system for that matter!
If it's that one with the big ports up by the thermostat housing, then you only need to use one on each side - one side only has one nipple anyway.
It is supposed to do two things - speed up the water pump and also the fan.
One nipple goes into the clean air side of the intake runner and the other into the plenum. It acts as a bypass to allow extra air into the plenum and the idle speeds up - that's all.
I use mine although I have an electric fan and temp sensor that I installed as it can tell me if for some reason my fan has failed to run. The engine will speed up and you'll know that something's happening.
Unfortunately there are multiple "thermal valves" on these engines and without a placement hint - it's kinda hard to say which one you are pointing to.