crazy temp guage

Rear, passenger side of cylinder head. 2 wire sensor. Very easy to access on a classic. Part# 23514708. Pretty cheap (under $35) 1" wrench. Be careful. When you remove you will have coolant shoot out at you. If you do it quickly you wont loose much. DO NOT swap when engine is hot.

 

I agree. two of my trucks did the exact same thing, pull the actual sensor itself and replace it out of the block. It's going to be very deep inside of it. Wait when shes cold before doing this work. Bet the farm the sensor itself would be rusted in some way or corroded. If the gauge has gone crazy then if there is a engine computer it would go nuts in time as well dealing with the crazy data flow.

It's routine. In the old cabovers we used relatively basic standard gauges, wires and sensor that went straight into the block and found some way to get power to them when in the dash ready to go.

Another possibility for a crazy gauge is you have lost enough fluid that is supposed to keep that sensor covered. If the fluid does not touch it its going to drop fast in temp. When additional surge of fluid managed to cover it back up it goes relatively fast. Until you lose enough coolant to be a problem elsewhere. I remember someone managed to use a icepick to poke a hole in the coolant line behind the turbo resulting eventually in a total coolant loss through that little hole. Would never have seen it if it did not coat the immediate area in that color when escaping that engine. Thats something we checked from that day to this.

Another time a radiator cap refuses to hold coolant pressure in the entire system. So it refused to cool, just splashed out all over the place.

I had a CAT that smelled of Coolant leak one day we could not find the source with the engine running. However when we shut down and she cooled off in the night until morning, the water pump seals allowed the coolant to escape and made a lake under the tractor. Dumped all of it. That was a surprise. Somewhat disruptive to the schedule for that particular load. By the time we got that fixed later in the day the rains came. And took care of that lake among everything else in that smelly lot. Fun times.

 

Just start unplugging stuff until it works,,,that's the biggest problem with 15-20 year old trucks. Electrical gremlins will drive you nuts.

 

News flash, they don't have to be 15 to 20 year old. The sensors that I have had to change on my 97 were changed before it was 3 years old, except the timing sensor, it made it 10 or so. Once they were changed though, they have held up to this day. I do have one electrical gremlin to work out, one of these days though.