Does this thermostat look okay?

I did the "dunk in boiling water" test to see if it would open.

It did, but not fully.

 

Here it is after cooling down.

 

When in doubt, throw it out. Are these inexpensive?

 

I have never tested a thermostat in my years of working on cars. If it's out, it's getting replaced.

What issue are you having?

 

They're $10-15 bucks

Maintenance item, I'd just replace it and toss that one out. It's such a cheap and easy item to replace there's no reason to run a bad one.

Can't forget the new o-ring too.