Reply to "Expansion tank cap"

First things first. A thermostat is a temperature controlled valve installed in the engine block under the inlet housing for the top radiator hose. The tank caps you refer to are pressure controlled valves. Your pressure tank needs a pressure rated cap, but the stock tanks require european caps - using american caps, due to the height of the tank neck, does not give proper sealing. Your expansion tank does not need a pressure cap but many, unnecessarily, have them. A non-pressure cap, as found on an overflow tank, will be what you use for that tank. Some stock pressure tanks have been modified with the proper height necks (you can have this done at any radiator shop) but you would be hard pressed to tell if that modification has been done. Most of the aftermarket SS tanks are built to properly use american caps.

Hope this helps.

Larry