So I'm new here with a 98 XJ Classic. I'm having this issue with my temp guage spiking and the check gauges light coming on. Its just the guage, the jeep isn't really heating up. I keep an eye on the temp with my OBD2 guage. I started with changing the temp sensor(cheapy from Autozone). That didn't work. I changed the thermostat(cheapy from Autozone) and replaced fluid. That didn't work. So I figured that there has to be air in the system and when an air bubble flows by the sensor it spikes the guage. I went and bought a no spill funnel and then jacked up the jeep on the drivers side and ran it for 30 mins jacked up I really thought that was gonna work. The heat works fine.

 

You are firing the parts cannon at a rapid pace. And its not really overheating according to your other gauge so why you getting parts and replacing them if its not overheating? Also Instead of buying cheap parts, buy better ones. Get a better temp sensor. That may do the trick. With xjs, they only like certain sensors and that may be the issue.

 

well I went to NAPA and purchased a temp sensor. Its 10 times worse. Temp guage was all over the place. So I purchased one of the Prestone T Flush kits. I'm gonna try that tomorrow. Its crazy the actual temp is fine on the Jeep. It has to be the temp sensor picking up air on the sensor to spike. Its strange now with the NAPA temp sensor the temp guage is staying really low and the fan is kicking on. Crazy

 

On a 98 the same temp signal-sender that drives the computer/ also drives the temp gauge...on the pre 96's there was a separate temp sender for the gauge....an open temp sender shows as a really low temp but signals an overheat to the computer and it puts the fan on. The factory sender is only a few dollars more than the auto part stores sender....is your 98 modified by prior owner...is there a sender on the driver side of the block near the firewall?....the computer /obd reading should not differ from the gauge...unless the gauge or wiring to gauge is bad

 

It's all stock. As far as I know the only sensor is in front by the thermostat. Most of the time it works fine and then it just spikes and then goes back to normal. I'm thinking there is air in the line and when it hits the sensor it just spikes.

 

Anything else going on? I'm thinking you may have a wiring problem. If it's not overheating, stop buying parts that would correct an overheating problem.

 

nothing else is going on. Its just the temp gauge is doing wacky thing. But I also use my OBD2 sensor and that spikes to 300 also and then goes back down. I've read to disconnect the battery to reset the computer.

 

sounds like wiring. I'm a control electrician by trade. Sometimes in my world I will run into a machine with sensor issues. I will replace the sensor and the problem gets worse.

What happens is when you mess with the sensor and task of replacing it, you will end up moving the wiring around causing the intermittent wiring issue to show itself.

Try jiggling the connectors and wiring harness while a friend watches the gauge. Also, look for warn insulation and or bad connections.

 

Well I starting thinking. This all started about a week after I removed my speedometer assembly to replaced 4 bulbs. A few of the bulbs were burnt out and I couldn't see the half the gauges at night. It didn't make sense to me that this would be related until I was just sitting in the jeep with the key on and the engine not running. The gauge was still pegging for a bit then going down to the normal 200 and then it would peg again stay for a bit then go back. Hell I needed a radiator flush anyways

 

Well the more I think about it. My OBD2 gauge still spikes up to 302 so that wouldn't point to the gauge having a connection problem. That information comes directly from the computer

 

Yep. That's what I'm thinking.

 

huh, doesn't your XJ have one temp sensor @ the t-stat? If my memory serves me correct. The older models had one at the back of the head in addition to the one in the t-stat housing. The newer models eliminated the one in the back of the head. Your reading the temp off of the ECU and it's the same sensor feeding both readings (ECU and gauge).

Edit: Also, if your gauge and ECU readings are experiencing the same problem. Then troubleshooting would tell you if two devices are experiencing the same problem. The problem probably lies up stream of both of those devices. I am speaking about the connection from the sensor to the ECU. Your temp gauge on your cluster is probably fine as well as the wiring to it.

sorry if there are typos I'm half drunk.

 

The temp gauge works fine. The temp sensor seams to work fine. I just disconnected the battery for a while to see if that had any effect. It seems like air is hitting the temp sensor and it's making the gauge spike and the OBD2 gauge go to 302. But I've bled and burped and run all the air to of this thing. I'm getting to the point where I'm just going to live with it but I'm afraid someday I'm gonna have an overheating problem and I'm not going to know it

 

FFS man, are you here asking for advice or telling us what you think the problem is? We are literally trying to give you ideas to check and you just keep telling us what you think the problem is. Like what is the point of this thread? It is all one-sided

 

OK how should I proceed? I've been jigling all the wires from the get go to see if it was kind of loose connection. Looking for worn wires. I haven't removed the plastic cover from the wiring rail inspect that. I've tried cleaning the connector that goes into the temp senso with a small file