Fj62 temp guage low (1 Viewer)

[Nick0615]

I have been battling overheating.

I have replaced the thermostat. Water pump. Fan clutch. Belt. Radiator (new aluminum mishomoto). Temp sensor and temp sending sensor.



After this last round of maintenance in which the pump, fan clutch, and sensors were all replaced at once I took it for a drive. When it was idling in the garage it was at normal temp, right in the middle. I turned it off and cleaned up.

2 hours later I started it up and drove it and the temp guage spent most of its time BELOW the first hash mark. It was almost as if the temp guage thought the engine wasn't even on half the time! Everything ran normal, upper rad hose was hot, and the needle did move slightly but it stayed very low the entire time. Below is a pic of me driving on the highway.

 

[pithicus]

Maybe your t-stat is stuck open. But it's new so not likely

 

[3_puppies]

without actual temps, it is hard to say what is going on
saying the upper hose is hot means nothing
did you install the upper gasket on the thermostat?
did you have any rags in hoses you forgot to remove?

 

[Seth S]

The factory temp gage isn’t the most reliable. Better to get one of those laser point and shoot temp gages and take readings around your engine bay. The factory gages can have wiring and grounding issues as well as sensor problems which give you false readings.

 

[OSS]

Check the wire connection to the temperature sender.
Everyone driving these ancient trucks should carry a hand held infrared temperature sensor gun in their center consol. They’re cheap. Harbor Freight has a pretty good one for not much money.

 

[Nick0615]

Check the wire connection to the temperature sender.
Everyone driving these ancient trucks should carry a hand held infrared temperature sensor gun in their center consol. They’re cheap. Harbor Freight has a pretty good one for not much money.

View attachment 2851196

What would you say is the normal operating temp and what area are you using the gun to read?

 

[OSS]

The thermostat is rated at 190°F, so should start opening at near that temperature when engine is warmed up. A good place to point the gun (I found) is at the front of the radiator top cap directly across from the big hose that feeds it (thermostat outlet).
It’s flat and black and directly across from the hottest coolant flowing into the radiator. It’s also easy.

You can try other places too, like back of the head, but after trying everywhere, it seemed that the top front radiator spot was just as good or better than any other.

Don’t waste your time pointing the gun at the engine block. The block is always cooler than the head.

On my 2F (not 3F-E) my temperatures I’d see with that gun could get up to 225°F when driving fast up a long hill, but idling temperatures after the engine warmed up and thermostat opened were around 192°-195° using that gun on the radiator top cap right side.

The 3F-E thermostat is rated to the same temperature- 190°F.
If you installed an aftermarket thermostat, Toss it in the trash and use only the Toyota unit.
Same holds true with the temperature sender. No aftermarket parts.

 

[Nick0615]

without actual temps, it is hard to say what is going on
saying the upper hose is hot means nothing
did you install the upper gasket on the thermostat?
did you have any rags in hoses you forgot to remove?

Yes thermostat installed correctly. Double checked with o ring. No rags anywhere, everything running normal.

 

[OSS]

The thermostat controls the temperature of the engine and it’s purely mechanical. If the gauge is reading low, it’s either the sender, the connection to the sender or the gauge that’s causing the low temp readout.

 

[pithicus]

If that temp reading in the pic is accurate your heater noticeably won't feel as hot as normal.

I installed a cheapo oil temp sender and it worked for a day or 2, then started reading really low like yours.
Not saying your sender is a cheapy, but you could try screwing the old one back in and try that.