Temperature gauge in 1999 Explorer barely working
 

Hey guys,

Having a problem with my temperature gauge inside the truck. No matter how far or long I drive, the needle barely moves off of cold. Would the thermostat be the likely suspect? If not, what else could it be? There is no "check engine" light on and my ODB2 reader reads a temp of around 70c solid. If it is the thermostat, where is this part located in the car and would I need to replace JUST the thermostat or are there gaskets/housing-type things involved as well.

Thanks in advance for your help.

John

The thermostat is right in the front of the engine inside the plastic thermostat housing.
It's pretty common for the long, skinny bolts to break especially if the housing has been leaking even a little bit.

There doesn't seem to be a problem with the interior heat. Would it be more likely to be the Sender than the thermostat?

70c either fahrenheit or celsius isn't hot enough, that is if your OBD2 reader is correct.
An engine that's running cold will run too rich, the extra gas will dilute the oil on the bores causing excessive wear. Blowby will dilute the crankcase oil.

You can take the thermostat out and test it for correct operation.

Assuming the truck you're referring to is the 4.0L SOHC Explorer in the signature block, there are two devices for engine coolant temperature - a sensor used by the PCM and a sender used only for the instrument cluster. The sensor is located near the front of the engine, left of the throttle body. It will have two wires to it, a Light Green/Red wire and a Gray/Red wire.

The sender is located near the center of the engine, behind the alternator bracket. On the SOHC engine it will have two wires, a Red/White wire and a Black/White wire.

On a few Fords I've run in to an "Engine temperature" parameter that never seems to change in the scan tool datastream mode. When I click on the "help" screen for the particular field, the note states the reading is for a downstream head temperature sensor and may not be available on all models. You might want to scroll through the datastream and see if there is another coolant temperature reading that does seem to track better.

-Rod

What is the proper operating temperature of the engine? Would replacing the thermostat correct this problem? Would replacing the sender do it or is there another solution?

Normal operating temperature would be around 180-210 degrees F. The thermostat is probably rated to open at either 185 or 190 degrees F.

-Rod

The upper radiator hose should get too hot to hold onto to.