OVERHEATING The truck is overheating but not showing that it is. Do I need to replace the thermostat?

Connie, Were the radiator,water pump and thermostat replaced to try and fix the over heat issue or as maintenance. Engine overheating can be caused by a lot of things, Leak in cooling system, air in system, bad rad. cap, slipping belt, faulty thermostat or installed upside down, faulty water pump, plugged radiator (inside/outside), collapsing rad hose, faulty cooling fan, leaking head gasket, sludge plugging engine water passages, poorly tuned engine, etc..
Take into a good shop for diagnoses and estimate for repair. Check the attached links,instruction and guides, Good luck
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How to Troubleshoot an Overheating Engine
Steve Litt Overheating Guide
Diagnose Engine Overheating Auto Repair Help
How to Troubleshoot an Overheating Engine DoItYourself com

might be a faulty water pump not circulating the coolant

have you tried to check overheat gauge?? some temperature sensor? isn't that faulty?? I don't mean thermostat, but sensor...

is it really overheating, or gauge is showing overheating???

long time ago I had car that had same problem.... never overheated, but still signalized high temperature.....that time it was temperature sensor probably not compatible with correct one ....

what is your model number is then we can get started then

Seems that your temperature sensor might be faulty, have it replaced, if the car drives fine, I dont see any other problem other than that.

Good luck.

I would replace the thermostat. Its a cheap fix and most likely the issue. If you replace the thermostat and are still overheating then you may have a more serious issue. But going 3 miles and overheating sound like the thermostat is not opening up at operating temperature.

it will be the senser mate ok, the engine senser, i hope this helps....

Overheating can be numerous things: Fans not working, water pump, thermostat, overflow cap, and the list keeps going. When the engine is running and heats ups, feel the heat of the top hose, if the hose isn't hot, the thermostat is most likely stuck open and needs replaced. If it is hot we know you have circulation. The cap on the expansion tank may be defective, if it can't hold the pressure of the water, it will release at the overflow cap if the cap is bad. Also check the coolant level.

sounds like you need tyo replace the thermostat

Is the car actually overheating? Are you adding coolant often or occasionally? Check your thermostat to see if it's working properly. If it's stuck closed, that's about how long it would take start to overheat. To check, remove thermostat, boil water in an old pot, drop thermostat in, it should open. If it doesn't, replace it.