i have a 98 with the 4.0 and today i replaced my coolant temp sensor because the guage was always reading cold, and would not move. i drove the truck after i replaced the sensor and still showes cold. what do i do now?

 

1)
There are two coolant temp sensors.

A two wire sensor reports the coolant temp to the PCM.
The single wire sensor is for the temp gauge.

If you replaced the two wire sensor, that has no affect on the operation of the gauge.



2)
Let say that you already replaced the single wire sensor and that didn't fix it. If the other gauges are working, then you know that the cluster has power and ground. Once you have eliminated the sensor, there is nothing to check except but the gauge and the red/white sensor wire.

 

Do you have heat?

 

i replaced the sensor with the single wire near the thermostat where is the other sensor located and yes all guages and heat work

 

You don't need to replace the two wire because it doesn't affect the gauge operation.

My next move would be to do a continuity check on the red/white wire. After that, all you have left is a problem with the gauge segment.

 

Check the actual operating temp to be sure, if it's not at least 190 at the engine your thermostat is most likely stuck.
You can do a quick test of the gauge by simply touching the single wire off the coolant temp sender to ground with the key on, (red with white wire as stated above).
The coolant temp sender reads between 74 ohms cold and 9.7 ohms when hot.
Lowering the resistance or grounding the wire should make the gauge read high.
If grounding the wire does not move the gauge, you either have a wiring problem or a bad guage.

 

got the damn thing to work. the probelm was the stoners up at murrays auto parts gave me the wrong damn sensor/sending unit. i went to my local auto parts store and got a diffrent one put that in and wala it works. now my truck shoulnt be gettting 7-10 mpg now maybe 14 or more lets hope
thanks for ur help and dont buy stuff from murrays discount auto

 

you could also put a seperate temp gauge like autometer...ect. with a seperate sending unit. I put mine in the steel pipe that goes to the return of the radiator.

 

You are not getting 7 to 10 mpg's because on the temp sending unit to the guage. That has nothing to do with the computer. It is only for the guage. If you are having temperature related computer problems you need to replace the other one on the other side. Good Luck

 

That steel pipe was your transmission fluid cooler lines. Did it have red fluid in it???

 

The upper rad hose with the tstat housing has a metal elbow.

 

I am having the same type issues and I am going to replace both. I got a code P0125. I have not had any overheating issues, but since I have had the truck the temp gauge either does not move (during the colder months) or moves little (during the hotter months) with the AC running. Do I need to drain the cooling system to replace these sensor/sender?

Thanks Jeff