Strange Temperature Behavior in 2000 Ford Explorer

I'm having a curious problem in my 2000 Ford Explorer and would appreciate any guidance anyone could supply.

The problem is that the temperature gauge on the dashboard normally barely gets into the normal operating range. Even on hot days with in-traffic driving, it barely makes it above the lower marking that denotes the operating range. On a cold day, it doesn't even make it that far, although it does move off its initial position.

The exception is when going up steep hills. In that case, the temperature gauge will suddenly climb back into the middle of the operating range, and will stay there as long as I'm going uphill. Once I level out though, or start downhill, it drops again.

Is this a thermostat problem, and, if so, how much of a hassle would it be for me to change it? The car has a 4.0 L OHV 6 cylinder engine with a 5 speed manual transmission.

Thanks in advance.

First thingcheck you coolant and make sure it is full.
Then make sure it is not just a bad tempture gauge or sending unit.
Check your actual engine runnng tempt.
Should stay in the 190-210 degree range.
Does the heater put out good hot heat all of the time?
MY

MY:

Thanks for the response.

My first thought was also a low coolant level, but when I checked it, it appeared to be ok. The upper hose from the radiator gets hot, but I don't know what the temperature is.

I get decent heat once the car has been running for about 5 minutes: not super hot, but enough to warm the car up.

Any thoughts on how to proceed?

mjs

MY:

Thanks for the response.

My first thought was also a low coolant level, but when I checked it, it appeared to be ok. The upper hose from the radiator gets hot, but I don't know what the temperature is.

I get decent heat once the car has been running for about 5 minutes: not super hot, but enough to warm the car up.

Any thoughts on how to proceed?

mjs

Sounds like your thermostat is stuck open. You can do it urself - you might want to get an explorer manual at the parts store so you have some instructions.