My 2003 Jeep Grande Cherokee V8 4.7L has been experiencing an odd problem with the temp gauge. I drove from Florida to South Carolina a year ago and it had no issues, thank god. But this past weekend I drop 200 miles and my temp gauge towards the end started to act up and would show that my engine was cooling fast when I was driving but rise back to 210 when I was stopped. I am not sure if its the sensor or if it is an air bubble in the system. It happened again when I was driving home from work which is literally only 10 miles at most from my home. It was fine with morning when it was cooler out, but driving home mid day with the heat, and it happened again. Any thoughts on if its a faulty sensor or if its something else? Im waiting till the engine is a bit cooler to check my fluids again to see, but as far as last week when I checked, literally everything was fine. Last time I had an issue with a faulty sensor was with my old truck and if causes my radiator to go out.

 

It might be a faulty thermostat? Maybe? I mean 210 is normal at rest idling.

 

Yesterday the wife and I stopped at a fast food place ordered and then sat in the car to eat for about 30 min at idle with AC on and it ran just under 210*. I have the same engine with stock cooling system as you.

 

I think I've diagnosed the problem as an open temperature sensor. It's a cheap and easy fix but I'm keeping an eye on it this week to see if my fluid change or if it's just a bubble in the system.

 

IDK if you are aware if this but the dash gauges are NOT directly connected to the sensors, but are activated by data sent from the PCM readings of the sensors! Like we really need the computer to tell us what the temperature is? SO... maybe it is a faulty sensor after all.

Like Fred/NOAZZ said, I've idled for hours and never had an overheat when the system is right. However when my fan was running slow because it was getting old and not running as fast as it should, then it got up to 240* before I shut it off. Even then, it ran normal when driving.

 

The problem isn't overheating though. I run average around 210 degrees and out of nowhere I saw the temp drop like 50 degrees and the engine wasn't hot after driving. The radiator fluid is lower than usual, but my car isn't sluggish when I go from 0 to 70. At a stoplight it sometimes will fluctuate up to 210.

 

That's unusual because an air bubble will usually turn to steam because of the hot pocket caused by it. Likewise, the steam pocket will show an overheat condition until it escapes. The thermostat is designed to maintain a set temperature and not let the coolant temp drop below it's set temp UNLESS it's sticking open.

 

That leaves us to the original statement that my gauge is stuck open and I'm burning radiator fluid faster than usual cause my engine to run cooler.

 

Say what? Burning radiator fluid?

 

Antifreeze fluid level is lower than it usually is.

 

Burning coolant? Got milky/sludgy foam deposits in oil or coolant? For oil, look under the oil fill-cap and in the fill-tube. Anything more than what's shown is here is abby-normal...

 

Nothing sludge like in anything. Just lower level of the fluid when my jeep has had the same level for 3 months. My dad said there might have been a problem with the gauge not being open before hand because I use to overheat when I was in Florida especially when my air compressor went out and the fan was disconnected. I got that fixed and everything was fine. I think the gauge was meant to go. The jeep has 400,000 miles on it and it seems to be the only problem is the gauge reading cold and my engine being cooler than usual. There's no sweet smell of radiator fluid, no leaks, just lower level if fluid my temp reading cold.

 

Whoa! 400K miles? Dude, you are blessed! You obviously also know how to take care of your rig. Let Dave1123 be your guide here, I'll defer to his advice 99% of the time.