Testing a thermoswitch

Now that my engine runs again, I'm getting ready to hook up an overheat buzzer I got from work to my late 80's Force 50. In order to make sure the system is working correctly, I want to make sure the temp sending unit (apparently called a "thermoswitch" by some parts websites) is actually working before I do any wiring.

I am assuming that at a certain temperature, the thermoswitch closes and creates a path to ground for the overheat buzzer, using the engine block as a ground point. If my assumption is wrong, let me know!

But assuming that is how it works, could I heat the switch up somehow (using a heat gun, or perhaps in a pot of boiling water?) and then check for continuity between the body of the switch and the wire?

I didn't see anything in my manual (not that I expect to) but if anyone has any advice or a better test method, let me know! Thanks!

Re: Testing a thermoswitch

Your assumption is correct about the switch. I don't know what temperature it closes. at but since 212 degrees is too hot for the engine, I would think that boiling water would close it. These bimetal switches are extremely old school, dirt simple, and almost indestructable. The only damaged ones I have see are screw in ones where the top has become disconnected from the body. I would expect that if the outside looks good, the switch will work, but it never hurts to check.

If your 50 has the type that plugs into a hole in the head, simply remove the circlip and pull out the wafer and rubber seal. If boiling water doesn't close it, try heating with a match or cigarette lighter.