Water Temp Low??

My 2000 GMC 4x4 5.3 will not heat up to normal operating temp (210 degrees) It will run around 175. It just started doing it yesterday. No reason, no codes. no, smells, no leaks, full radiator (not overfilled) What am I missing?
Thanks

My 2000 GMC 4x4 5.3 will not heat up to normal operating temp (210 degrees) It will run around 175. It just started doing it yesterday. No reason, no codes. no, smells, no leaks, full radiator (not overfilled) What am I missing?
Thanks
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Thermostat stuck open?

Bob B

I considered that but usually when a thermostat is stuck open the engine will overheat due to flowing too fast through the radiator. Unless there is enough restriction in the normal flow to slow it down. In my race truck I had to use a restrictor washer ( no thermostat) to slow it down to have time to cool.

Thanks

I had my 96 GMC do the low coolant temp . it was like that for almost a year until I decided it was a bit to cool for the winter months. so I pulled the thermostat out and found that a little piece of the thermostat had come loose and was just enough missing to keep the cooler temp. when I replaced it back to factory it rose back up to the 195 degrees.

I have never heard of a thermostat that is stuck open causing a truck to over heat. I have had to remove a t-stat from a vechile that was over heating to get it home.

My race truck will overheat without a restrictor in the system... but you are right with a stuck open thermostat there is enough restriction in the thermostat itself that it will not overheat.