I have been dealing with the same problem for a while, I found this thread (https://mitsubishiforum.com/forum/showthread.php?p=225427) with a possible solution. let me know what you guys think

 

I'd say it sounds pretty straightforward; if your gauge is reading hot and your engine isn't overheating and your sensors are good, then it's time to be looking at the gauge itself. Unfortunately, I haven't delved into the gauge clusters of these vehicles, so we'll have to wait for someone more knowledgeable than I am to pipe up with any specifics you might want before you go poking around in there.

I do know that if your beast is similar to mine, the temp gauge is a separate unit so you should be able to find a spare one and plug her in.

BTW, you should update your avatar so we'll know the vintage of your ride

 

I am having the same problems as the initiator of this thread is having. My 02 Montero is overheating. Took it to one shop and they said the water pump was bad after they replaced the thermostat. The water pump has been replaced less than a year ago ( I dont think that is it). Took it to the dealership and was told the condensor fan was bad. Replaced that (and the fuse which the dealership didn't catch). Dealership said the gauge is working. Any Suggestions?