Since someone else got on the subject of a problem with there computer, I figured I would ask about mine. I have a 98' Ram 1500 with only the compass and thermometer on it. Sometimes when I turn my truck on the meter reads some crazy temperature, a good 25 degrees sometimes. After I begin driving the temperature drops to normal after about 5 minutes.

Is there something going bad with the sensor or is the thermometer located in the engine compartment? I have no idea, it doesn't really bother me but I would want to know what is going wrong.

Thanks,
Mike.

 

It just gets hot under the hood sometimes.... or stays cool if the truck hasn't been run and is in the shade.
Can't think of any other reason it would be showing an incorrect number and then return to "normal" after a little bit of driving.

 

It is normal for the temperature reading to be false when first getting in the vehicle. The sensor is located under the hood, actually behind the grill in front of the radiator, to the side, and as you might imagine this could give different readings dependent upon whether or not the engine was hot or the truck had been sitting in the sun.

After the truck starts moving and the air has time to circulate around the sensor, the reading should return to normal. If you are driving under 20 MPH or doing a lot of stop and go driving, the unit updates much less frequently.

 

I get about 5-10 degrees variance on mine after it is hot and stopped then started again. A 25 degree difference is not extreme depending on where you live and how hot your engine is getting.
Here are a few tips I saw from another post somewhere.

Make sure your temp sensor is clean - dirt, grime and grease on the probe will hold heat or throw off the temp. Make sure the connections are clean and secured in place. Use another thermostat and place it near your temp probe when you engine is cold, then try it when it has reached normal operating temperature to see if there is a significant variance.

If there is a big difference between the two temperatures then you should perform further diagnostics on the probe to see what the issue is.

DIAGNOSIS AND TESTING - AMBIENT
TEMPERATURE SENSOR
(1) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Disconnect the ambient temperature sensor wire harness
connector.
(2) Measure the resistance of the ambient temperature
sensor. At –40° C (–40° F), the sensor resistance
is 336 kilohms. At 55° C (140° F), the sensor
resistance is 2.488 kilohms. The sensor resistance
should read between these two values. If OK, refer to
Diagnosis and Testing - Ambient Temperature
Sensor Circuit in this group. If not OK, replace the
faulty ambient temperature sensor.

DIAGNOSIS AND TESTING - AMBIENT
TEMPERATURE SENSOR CIRCUIT
(1) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Disconnect the ambient temperature sensor wire harness
connector and the Front Control Module wire
harness connector.
(2) Connect a jumper wire between the two terminals
in the body half of the ambient temperature sensor
wire harness connector.
(3) Check for continuity between the sensor return
circuit and the ambient temperature sensor signal
circuit cavities of the Front Control Module wire harness
connector. There should be continuity. If OK, go
to Step 4. If not OK, repair the open sensor return
circuit or ambient temperature sensor signal circuit
to the ambient temperature sensor as required.
(4) Remove the jumper wire from the body half of
the ambient temperature sensor wire harness connector.
Check for continuity between the sensor
return circuit cavity of the Front Control Module
wire harness connector and a good ground. There
should be no continuity. If OK, go to Step 5. If not
OK, repair the shorted sensor return circuit as
required.
(5) Check for continuity between the ambient temperature
sensor signal circuit cavity of the Front
Control Module wire harness connector and a good
ground. There should be no continuity. If OK, refer to
Diagnosis and Testing - Overhead Console in
this group. If not OK, repair the shorted ambient
temperature sensor signal circuit as required.
REMOVAL
(1) Open the hood.
(2) Disconnect and isolate the battery negative
cable.
(3) Working on the underside of the hood, remove
screw holding sensor to hood panel.
(4) Disconnect the sensor electrical connector and
remove sensor from vehicle.
INSTALLATION
(1) Connect the sensor electrical connector.
(2) Working on the underside of the hood, install
screw holding sensor to hood panel.
(3) Connect the battery negative cable.
(4) Close the hood