thatXJguy

So I'm having a weird scenario with my temperature gauge on my 99 XJ.

When driving, my temp gauge says my Jeep is operating at about 130º.



When I stop at a red light, my temp gauge says my Jeep is operating at my typical operating temperature.



I have a brand new thermostat in there and I don't appear to be leaking coolant.

Any ideas why it's doing this before I go buy a new sensor?

SteveMongr

The sensor can be tested. Not sure exactly how. Big help I am, lol.

1976gmc20

Yeah I think it's supposed to be X amount of resistance at Y temperature. Somewhere I found a pdf manual that has all that stuff.


But I would be looking at the fans

98XJSPORTSATINJADED

Funny I had the same issue with no coolant leaks and it turned out to be a split heater hose.Ever since i replaced the heater hose temp gauge works at norm.

thatXJguy

I have all new heater hoses.

I just did a power flush today at my local shop. So far so good since the power flush. I will report back after a week and let you know if the problem comes back.

thatXJguy

It's happening again tonight.

What is the relationship between an idle that is about 100 RPM higher than it should be and a low coolant temp reading?

pisspoorxjguy

Just gettin goin in the grand scheam of things but I know I was idling high, I cleaned my throttle body made sure all air lines were good nothing unplugged, and also scraped the paint of my fire wall behind the ground and cleaned all corosion idled perfect

thatXJguy

I'm not idling high unless the temperature sensor acts up. And even then, it's a very small amount. Like 50-100 RPM. I just cleaned my TB last month.

I don't know how often temp sensors go bad on these things, or if the sudden temp drop while driving could be something else?

1976gmc20

Any engine is going to normally run cooler when more air is moving through the radiator (as in while driving).


Is the temp dropping while driving, or going up while idling ???


That's why my uneducated guess was maybe your fans aren't working optimally.

SteveMongr

ECT sensor is used to determine injector pulse width..

.."Related Symptoms to faulty ECT sensor. Not Jeep specific.

Extended crank time when the engine is cold
Poor fuel economy
Spark knock
Lack of engine power
Erratic and/or high idle
Engine cooling fan stays running all the time
Engine cooling fan fails to turn on
Engine overheating"
http://www.freeautomechanic.com/ect-...mperature.html

thatXJguy

We're talking 100 degrees cooler than it should be (or so the sensor says). That doesn't seem normal to me?

The electric fan isn't on when I drive. Unless it goes over 210, which it rarely ever does. The clutch fan only spins at the speed of the engine.

thatXJguy

I've never heard of an ETC sensor before. Where is that located? I Googled it and many of the search results are leading me to the coolant temperature sensor.

SteveMongr

^ Correct ECT = Engine Coolant Temperature.
On my 1996 it is in the thermostat housing, there is another at rear of engine that is used for gauges.
Later models, there is only one ECT, located at top-rear of block, it is used for dash gauge and jeeps computer for calculating injector pulses.

thatXJguy

I think my sensor plug was just loose.

I pushed it in more and the gauge started working again.

Cheddarnut

I don't know about you but I'm always happy resolving a problem by plugging something back in. Was it at least a pain to reach, maybe a busted knuckle? That would be more Jeep like. Just saying.