interesting overheating issue

I was driving my mothers '89 Escort, and I was very slowly plodding along in really bad traffic. When I looked down, I noticed that the temperature gauge had spiked to HOT, so I made my way to the shoulder. Interestingly though, when the temperature gauge started getting really high, the fuel gauge started going up. When the engine was at HOT, the fuel gauge said the tank was FULL, but I know that before this the tank was only about half full.

Has anyone seen this sort of strange cross talk between the gauges?

High temps can cause all kinds of readings. Was the car actually hot? Put a thermostat in it an reply here.

That was the only time that has happened. There has been some intermittent heating issues, where the temp will go up to new HOT and then drop back down to the usual operating temp, but this time it stayed pegged. I can't make it happen on command, nor can I predict when it will happen to put in a thermocouple.

The temperature gauge and fuel level gauge share a common ground. Too much resistance going to the gauges will make both inidicate high. Check the resistance of the ground wiring. You might have to pull the gauge cluster to check the ground which is a black and green and solid black wire. Also, check the wiring from the temperature sender at the engine. I wouldn't worry about a false intermittent high reading on both of the gauges. It's just a ground wire that isn't making a good connnection. If it was me I wouldn't worry about it too much.

How about an intermittent temperature reading? It sounds to me like it might also be a grounding issue then.

First things first. Clean and tighten the battery terminals.