Erratic Engine Temperature

Hello

The temperature reading on my 1998 Explorer 4L V6 has been a little eratic resently. From cold the temp builds up to almost over heating then it drops rapidly back to normal operating temp. It then moves up and down the middle of the temp range for the rest of the journey with the odd trip back up to overheat.

Any ideas to the problem? Could it be a dodgy thermostat?

Thanks

Andy

While you are driving, is the heat coming out of the vents warm, or more cooler than normal. I encountered a similar problem on a different type of vehicle and it turned out to be the water pump.

While you are driving, is the heat coming out of the vents warm, or more cooler than normal. I encountered a similar problem on a different type of vehicle and it turned out to be the water pump.

thermostat is cheap and easy to replace, good place to start.

Friend of mine had a similar problem with a van of his. It turned out the erratic indication was from trapped air in the system. The indication was from the sensor going from sensing water to air (which it can't do). He removed the upper radiator hose and found some fibrous gooey stuff blocking the inlet to the radiator. This is probably not a common thing, but if the new thermostat doesn't work, you may want to take a look at something like this.

I'd put a thermostat in it before anything, I've probably done a dozen 4L water pumps and a thousand thermostats. They're kinda known for t-stat issues.