I tryed to test my thermostat in boiling water... but I didn't see *anything* budge, although I'm not really sure what I'm supposed to be looking for... is it supposed to contract and move that washer thingy inwards? Because it didn't...

Also, it's basically accepted that only OEM thermostats are worth using, right?

I did have pressure in my coolant system, since there was pressure when I took the cap off, and because it blew white coolant smoke out of my bad coolant seals (working on that... I got the flywheel nut off but now I need to borrow a puller), but can you still have pressure in the coolant system with a stuck thermostat?

Well, any advice?

(One more thing: am I supposed to replace the water pump if it's all rusty-looking, even if it still spins?)

 

Yes it's recommened to use Mazda thermostats only.

As for the water pump, if it has rust on it then it's probably old and could need replacing but may not be necessary. Check for any wet spots at seems and sniff around for a sweet smell (antifreeze). If you know the age of your water pump then it would help out your answer a great deal.