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So this is my temp gauge after running for over 20 mins. The gauge always seems to run around this temp on the highway. The only time it creeps up is in traffic and on trails. The truck runs fine. It just looks weird. Ik the saying “if it ain’t broke don’t fix it” and trust me i won’t. Just wondering if anyone has an explanation. Thanks

 

Could be the sender is reading off some, or it could be the gauge isn't indicating the information it gets from the sender correctly. These gauges are notoriously inaccurate.

I'm not certain, right off, what th sender should indicate, as far as ohms, for specific temps. It should have specific ohms for specific temps. Like, and this is ONLY AN EXAMPLE, for 65° F, 100 ohms, for 150° F, 500 ohms, or whatever. That would change the current through the gauge as the temp changes, causing the gauge to indicate the temp.

On the other hand, it could be that the gauge is indicating something other than the system is designed to indicate. that for a specific value of the sender, it should read at 1/4 deflection, but only reads at 1/8 deflection. Sometimes tha solder joins on the circuit card the gauge is mounted on either aren't the best to start with, causing the gauge to be off, or have slowly gotten "badder" over time, as the circuit board flexes as the truck bounces around.

I would say get a remote reading thermometer at Harbour Freight, or wherever, and when the truck s good and warmed up, point it at the thermostat housing. I'd bet it will read 185 to 195° F. Look and see what the gauge indicates at that point. That's your truck's "normal" indication.

What's really important, in this situation, is does the gauge read higher and higher as the temperature of the water goes higher. In other words, will the gauge tell you there's an incipient (big word, huh??) problem, or an actual problem, situation occurring. THAT'S the key.

Not super helpful, but the best I can offer...
Pat☺

 

I might remove the temperature sender from the engine and see just how much rusty crap is about the sensors cylindrical probe. Is this a 22R? Cleaning up the electrical contacts might prove a good idea and perhaps reconnect but with dielectric grease added to the conductive terminals.

 

If, and it's a big IF, it were me, I'd be more worried about what corrosion had built up on the threads. The cleaner they are, the more accurate the information the sender will provide. That's it's path to ground, which is the really crucial part of the circuit.

Mine are one of each. A 22R, and 22RE in the 4Runner. Or did you men the OP? If you did, ignore my interferance.


THAT is a super-good idea.

Pat☺

 

That's a freaking horrible idea especially without the explanation that dielectric grease is non conductiv and that it will turn a loose shady connection into a no connection.

You need tight clean metal to metal contact between the male and female lugs of the temp gauge sensor, as well as your grounds (block to battery, body to battery, head to battery, dash to body).

Cleaning the scale build up off the sensor, which is effectively and insulation, will make the guage more responsive.

cleaning the sensor body and the intake threads, are very much a good idea. This is the ground portion of the sensor.

This is a hot wire bimetallic guage, the lower the sensor resistance the more the current and thus heat in the bimetallic spring in the guage moves the needle. I hope you can see that all the junctions in the circuit add to the resistance the guage uses..

 

I had similar and read to pull the gauge cluster and clean the contacts on the back with electronic cleaner. I did all the instrument contacts while I had the cluster off. Fixed the low reading.

Some time later the oil pressure gauge was reading zero at idle and only 'idle level' when doing 65 mph. I replaced the sending unit with an OEM Toyota and read normal pressure. I always use OEM for sending units are had issues with universal aftermarket. For as long as they last worth the few bcuks more

 

a new oem sender from Toyota (83420-20020) should be only $25.00. If you decide you need a new sender it'd be worth the peace of mind to get this over aftermarket.

 

If the gauge is bad, why does it move up at all? Well, it is possible, but I would be sure to consider that your thermostat is not closing. Air running through the radiator is keeping the coolant cool, just like your gauge says, until you get into a situation where your cooling breeze goes away.

Get an inexpensive infrared thermometer and read the temperature right on the metal of the thermostat. Do it after you've been driving a while; as you sit there idling the temp will come up.

 

I had this exact issue and it was the thermostat not closing.