Ok, have a ques for the forum nobody seems to be able to shed some light on so far. Have a 2000 Sierra that won't get up to temp. Gauge sits just above 160, infrared on the water outlet says the same thing. Have tested and installed 2 additional thermostats, each open at 190 or so and close at 180. No change in the vehicle. Water pump and radiator were replaced 9 months or so ago, no problems until recently. Temp will occasionally reach "normal" on the gauge, then drop randomly, mostly on the highway. The engine is physically running cold, and the mileage has suffered as a result. After sitting with the engine off and heat soaking, the temp rises to 174, then after 20 seconds of running, it drops to 155 or so. Any ideas?
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