Just put it in a with water filled pan on the stove , heat on.
When the water reaches the boiling point , the thermostat has to open slowly.
Goes it open a while before your water is at boiling temperature ( let's say , @ 100 °F ) , is your thermostat toast...
Does it not open at boiling temperature , is your thermostat toast also, but don't be surprised when your engine turns from a gas engine to a steam one
I had to put a new thermostat in my Impala , as the water temp won't rise : there was no thermostat at all...
Before I've put the new thermostat in the engine , I did the test.
No problem at all...
The Baron
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1979 C10 LWB , 350 Oldsmobile engine , rusty stock
1977 Impala sedan , 250ci , "Ye Old reliable"
1960 Girl friend , frame still good , body has some dents
