93 toyoya truck getting hot, not the bunnion

Have a '93 Toyota truck. Only 100K miles. Today, noticed the gauge near the hot mark. The engine was not hot. It did not expell coolant and the engine and radiator were normal. (about 190 per the test probe all over) I am old school. A clogged radiator does not show overheating without warning. I need your help and owner/mechanic experience with this year Toy. A thermostat does not usually close after opening especially after getting to operating temp. I am thinking the gauge or sending unit? What do you smart folks think? If you agree, where is the sending unit? Please don’t say under the #5 main cap attached to the fuel injector fusible link. Kidding, but new tech. has made me suspicious in some cases, even early 1990’s … Anyone out there with a similar “I know that one” answer? Thanks. Not a nummy, just tired of pulling the fenders and entire front suspension off to find the engine. Woody

On a vehicle built two milenniums (baloneyums) ago like yours, the radiator fins could be completely gone. That’s between 5% and 10% rusted away. Check it from the rear with the shroud pulled back if you can’t see them all. If that is the case, it will overheat soon, probably within the next six months, if not next week.

Fisrt let me clarify a misconception. A thermostat’s function is to keep the engine temperature up to full operating temp while at the same time allowing sufficient coolant flow to prevent overheating. In cold weather a thermostat can, in fact, open and close, and can even stabilize at partially open.

A vehicle this age needs a good thorough going over. There could easily be more than one part of the cooling system that needs addressing.

Wow, my old school training worked. It was in fact the thermostat. Hey friend, 93 Toy was one of the best and for your information, the radiator fins do not rust. They are non ferrous, no iron to oxidize. My suspicion was late, but correct. For your information, a thermostat I learned, (yes I learned also) does the following. What happened, the thermostat opened/closed on and on, Finally, it corroded and after parking for 20 minutes and cooling, it closed, then did not open fully. After a replacement, it ran so cool, as if I installed a new radiator.
I, looking for black helis copsters going into those walls. (Katrina) pried way ahead and considered the sending unit. Wrong. Cover the basics first. For me at least. Radiators don’t clog overnight. (unless you have a liberal neighbor) It is either the thermostat or gauges, or idiots lights. on that dog. Especially if it happens suddenly.
Late post, got it right so had to do it. So long since a post, not sure if it goes to the front of the line. Sorry if it did Woody.