Cooling Issue

AJ/FormS said

Under steady state conditions you shouldn't be seeing the water temp going up and down.The stat just does not work that fast! What I would do is grab an old stat and cut everything off it so that you are left with just the restrictor. Install that and roadtest it.

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This test is next on the list. While driving it yesterday, I noticed the temperature swings even after 30 mins of driving. It would climb to 220, then drop down to 190 very quickly and stay there for a while before climbing quickly to 210-220-ish and back down. I'm suspecting an issue with the thermostat.