Temp Gauge issue

[Pat McMurray]

My '87 FJ60 was sitting for many years. Finally got her running but I've been chasing an overheat issue. I've flushed it 3 times and it needed it, the coolant looks good now but according to the gauge its still overheating. I've changed the sensor and recrimped the wire. Sometimes the gauge goes so far to the right that the needle seems like it should bend, then right back to normal (within seconds). I've checked the actual block temp and it's 180. What I just noticed today is that at the same time the fuel gauge does the same exact thing at the same time. So it has to be an electrical issue. Any clues where I should look first?

 

[Ben Stratford]

My 60 used to do the same thing occasionally. Both the temp and fuel gauges suddenly max out at the same time having been normal.
Traced it ti a bad connection at the temp sensor. I polished the connector on the sensor as it was tarnished and fitted a new spade connector as it had become worn and loose.
Its worked fine since.
Hopefully it will be similarly straight forward for you pat

 

[alexy]

its widely covered on ih8mud. its called temperature spike.

Could be sender, or old connection.
The fuel gauge has in it a voltage drop unit from 12v to 7v. thats where usually problems are.
There are mechanical contacts there that can be cleaned. some guys change resistors there. or use another voltage convertor.

same happens in 70s (like mine).
I used to get the spikes, but fuel will jump usually when the fuel tank is full. with fuel tank less full , only temp needle will spike and would give a "oh shit" moment.

be very careful if you choose to clean the regulator contacts. I did on the old gauge and it throw out of normal the readings, not they were accurate anyway.

 

[Pat McMurray]

its widely covered on ih8mud. its called temperature spike.

Could be sender, or old connection.
The fuel gauge has in it a voltage drop unit from 12v to 7v. thats where usually problems are.
There are mechanical contacts there that can be cleaned. some guys change resistors there. or use another voltage convertor.

same happens in 70s (like mine).
I used to get the spikes, but fuel will jump usually when the fuel tank is full. with fuel tank less full , only temp needle will spike and would give a "oh shit" moment.

be very careful if you choose to clean the regulator contacts. I did on the old gauge and it throw out of normal the readings, not they were accurate anyway.

 

[Pat McMurray]

Already installed a new Temp sensor, reterminated the spade connection going to it. Traced and checked the wire into the bundle and it looked good. It sounds like I need to look at the fuel gauge and at that circuit. I have been so fixated on the temp sensor that I had not thought to look at the fuel as the culprit.

"oh shit" is correct, I'll bet the fuel gauge was doing that all along but it didn't notice till yesterday.

Thanks all!