Cooling fluctuations

So, my mother has an '89 Escort (LX), and I can be driving along, with the coolant temp guage will be hovering around the M or R in NORMAL, when randomly the needle will start up to HOT or at least N, and then go back down to where ever it was, all in about the time it takes to drive a couple fo blocks. Any thoughts?

Maybe the thermostat is not opening soon enough? Once it does the temp cools back down.....

try removing the wire to the temperature sensor and cleaning it up, could be bad connection with corrosion and cheese growing in there. I've seen it happen before where the temperature gauge goes all over because it has a bad connection or the wire has worn through against something and is grounding out.

The switch for the fan may also need cleaning. When was the last time the cooling system was flushed?

Could be the thermostat sticking or the coolant fan temperature sensor is going bad. Find the fan motor wires (colors) and find the fan relay on the fender wall by these unique colored wires. The other wires from the relay go to the sensor. It is either located near the thermostat or the radiator itself. Been awhile since I worked on an Escort. But all electric fan systems are the same.

They consist of the sensor which turns the relay on which turns the fan motor on. I see so many people short wiring the fan or putting a toggle switch in when really it's real easy to troubleshoot once you know the 3 parts of the system. Fan motor, sensor, relay. 4 if you want to count the fuse, lol.

The switch for the fan may also need cleaning. When was the last time the cooling system was flushed?


That is a very good question. I don't rightly know, so I guess it will go on the list of stuff to do.

My vote goes for sticky thermostat. Like it's trying to open, but not until it reaches a few degrees above it's rating, so when it finally does open it brings the temperature back down to its rating.