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how about using an infrared heat gun to check the top and bottom of the radiator, as well as the heater hoses, to get some idea of how hot the engine is actually getting ?


"Correcto"
Folks will spent $hundreds on cooling system parts to fix heating issues,
But don't have, or use, an infrared temp gun.
Being so cheap these days, they should be as common as an adjustable wrench.
Best "tool" to have when questioning accuracy of gauge, digital or analog.