Trying to replace thermostat on my van... one problem I can't find my thermostat housing. I know that sounds silly but after looking for it near the top side radiator hose no luck.When I bought the replacement the auto parts store told me it was inside my radiator cap (on top of the radiator) I've never heard of such a thing. The only ones I've ever dealt with were on the engine side of the top hose.  Are they right and if so how do I open that cap since it says it is pressurized and should not be opened like a regular one?  I'm out of a vehicle right now so anyone who can tell me where the heck this is located would be great. This should really be a simple fix and I'm just lost right now.