1975 Evinrude 6hp Thermostat Question

I had posted a thread a month or so ago and someone had suggested I check to see if my thermostat was working. I opened the thermostat cap to have a look, it didn't look like it was stuck open, but while I was in there I decided to check that it was opening properly. I heated some water to 150 degrees, but I'm seeing very little change. It may have opened 3/16" or maybe I'm fooling myself. How much is the thermostat supposed to open if it's working properly? Is it supposed to move fairly quickly? Do I need to heat the water more? It's a fairly cheap replacement, so I'm leaning toward getting a new one.

They usually fail stuck open.------No worry that they stick closed.-----I use boiling water and they open fully in seconds.----Good to go.

I ran a couple more tests, it opened at 190 degrees, although not quickly. It stayed closed at 165 degrees. I see on the replacement thermostats that they're supposed to open at 143 degrees. Does it matter if it has to get to 190 degrees to open?

It does matter if it truly is that hot. Which I sort of doubt (??).

Last test I ran, put it in 190 degree water, watched it go from fully open to fully closed. Ended up fully closed at 160 degrees. Given the cost of a new one I'm just going to get a new one so I don't have to worry about it.

Swarlos said:

Last test I ran, put it in 190 degree water, watched it go from fully open to fully closed. Ended up fully closed at 160 degrees. Given the cost of a new one I'm just going to get a new one so I don't have to worry about it.

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If it does not start to open until it is over 160F then it is definitely defective and should be replaced