Gauges

We might get a better idea to help with your problem if you tell us what kind of truck and engine you have. I never heard of a engine water gage?

 

Your engine temp gauge is bounding that hi from either being low on water (gauge peds in air) or you have combustion (head gasket, air comp, whatever).

The four gauge sendors you CAN have on coolant:
1) Coolant temp (1 pole, 3/8" nut)
2) Overheat idiot light sendor (1 pole, 11/32" nut, red top)
3) Low coolant sendor in the rad (3 or 4 wires depending on external grounds)
4) Horton (Bendix) fan switch (two poles; hot in, power feed out)

Running the fan full time drinks fuel, and you're not fixing the actaul problem. Good luck tho!!...

 

International only has one gauge for engine cooland temp. Chances are the second gauge is either a custom installed gauge or a second water temp gauge in the engine oil temp gauge spot. (some you can switch spots) The fan switch will be for the engine fan. If your gauge needle is boucing around really quickly then you will have a bad sensor or wire. I would need to get my manuals that I don't have access to a home, but I think you would have just a single wire temp sensor somewhere near the waterpump or rear of the oil cooler. With the age of the truck, I would bet the wire is corroded or loose somewhere. If the needle bounces really fast I would say it is a gauge/sensor/wire problem. You have realize that engine coolant doesn't change temperature that quickly. It takes a while to warm up and cool down, it is a slow process.