So I have a 1998 ram 1500 5.2 auto. My coolant temp gauge is reading low currently. I have replaced the water pump. Thermostate twice now cause it was in my plenium gasket kit. I have tried to replace coolant temp sensor with single pin and double sensor. Both read that it is low. I am also having the issues of rough idle and dying when coming back down in rpms. My idle air control valve seems to b working correctly but have a new one on the way to take that out of the question the truck has a full new tune up i am wondering if anyone has a fix for this or a way to bypass this for the engine to run correctly and just use a store bought gauge thanks in advance

 

Your truck only has one temp sensor, and both the gauge, and the PCM use it. Need to find out if the sensor is simply mis-reporting, or there is some other issue going on. Check temp with an IR thermometer, and see if the gauge is actually telling the truth. Might also plug in with a scanner, and see what temp the PCM thinks the engine is.

 

The 98 model year has a sensor with two pins which both connect back to the PCM. As HeyYou wrote the sensor is used for both engine management and the gauge. Below is a table of what the sensor should read at different temperatures. Also consider that bad wiring might cause the PCM to read high resistance which is interpreted as low temperature.

 

Judging by driving my truck for 20 min just now and being able to hold my hand on the coolant hose says that a brand new thermostate is stuck open?

 

I currently have the double pin sensor hard wired in to the harness that Is sotterd and installed cleanly. Would reversing the wires make a difference to and as for being able to hold the hose that was out of the raditor side so the cool side back into the engine but I also have id say decent heat also to show more that it is up to temp.

 

Ok sorry to be so annoying with bad info it seems like the brand new thermostate is stuck open. From testing temp in the raditor I was getting 125 gauge is reading around 140 so backwards from what I think that the temp sensor is correct but has something to do with thermostate

 

Having the sensor backwards will not affect anything. Resistance is resistance.

I'll say it, any chance you put the thermostat in upside down? Wouldn't be the first time I did it. Double checked for air in the system?

 

No its totally fine I honestly thought the same thing. I checked the Chilton manual I have from napa and it was in correctly. I just went through and replaced the theromostate with a new one from napa and I gained ground on the temp gauge I'm about half way to 210 with a 195 state. I did test the state before I put it in the truck and checked out ok so I guess I'm still stumped on why I'm not there yet endless its just the cluster is off and my IAC valve is bad

 

Plug in with a scanner, and see what the PCM thinks engine temp is. (your local parts store should be able to do that for you.) I went from a 96 truck to a 98, and the temp gauge on the 98 reads WAY different than the 96 did. To the point that I thought I had a bad thermostat as well, so, I changed it, only for nothing to be any different.... Plugged in with a scanner, and low and behold, 195 degrees......

 

I have just gotten used to mine not reading properly. Might actually go plug in the reader and see if mine actually runs right or not.