Testing thermostats
 

My '53 flattie doesn't seem to be indicating temp properly. It's full H before I fire it up and then full cold after that, even after idling until it's clearly warm. Can you test sending units by checking the resistance through them at various temperatures? What should the two (different) sending units read?

-Scott

I can't help with the figures, but your gauge is working properly - H at rest, then moves to C with key on. It should move up as the engine gets hot.

The single pole sender is just an on/off switch that spikes the temp gauge when it reaches a pre-set temp.

The double pole sender is the actual variable sender that indicates on the gauge.