Temp gauge problem

[jeepzj]

Weird thing I noticed driving home from work today. While driving and up to normal operating temp the needle stays at a steady 210 or slightly below all the time....normal. Today the temp gauge dropped a few needles then went back up to 210 in a mtter of seconds. It did this a few times. Also, for a good amount of time while driving 45mph or so the temp needle stayed at two lines below 210 then jumped up to 210 while sitting at a light. I'm thinking a bad temp sensor? Has anyone ever experienced this. This is for a 1998 ZJ I6 with 124K miles.

Thanks.

 

[Brandon]

I took a couple of pics this morning with my phone cam.

This is how far down it dropped while driving to work this morning for an hour then went back up to 210 then dropped back down a few notches. It eventually went back to 210.

210*. This is where it stays at normal operating temp when the gauge isn't wacky:

Thanks.

 

[johnd]

It certainly is possible for a sensor to fail. I had one on my Camaro do that. It would drop to zero (open) and register the correct temp every now and again. It didn't act like your gauge is showing so that might not be your problem. If you have heat gun you might check and see if the gauge is actually tracking the engine.

 

[Quest]

lemme see: temp sensor problems, wiring/connections problem, gauge going bad, last but not least: possibly a bad thermostat as well.

 

[Brandon]

I would not think of it being a thermostat problem since the gauge flucuates too quickly. I'm thinking temp sensor which I think is mounted right on the manifold.

 

[MarkC]

Put a jumper on the sensor and see what the gauge does.

 

[fatjack]

I would check if it has enough coolant and has no air bubbles in the block. Just burp it to be on the safe side

 

[Brandon]

Quote:

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I would check if it has enough coolant and has no air bubbles in the block. Just burp it to be on the safe side

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Coolant is full and no air bubbles.

 

[CBDFrontier06]

The oil temp guage I installed on my 74 Beetle did this when the connection to the sending unit got loose, but didn't totally disconnect. It would be reading steady at 225 and then suddently drop to about 1/2 that, and the zoom back up after a few more miles. Tightened the connection and it stopped.

 

[mechtech2]

My first guess is air in the system.
The sender, wiring, connections, or gauge are next.

 

[jeepzj]

Quote:

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My first guess is air in the system.
The sender, wiring, connections, or gauge are next.

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Next question I pose is where is the sensor that controls the temp needle on the dash?

 

[mechtech2]

Sorrry - I don't know your particular engine.

 

[ThirdeYe]

I'm thinking coolant temp sensor. I had an issue on my old Altima where it would fluctuate or sometimes not read the temperature, or jump all over the place. Turned out the sensor was somehow loose, because the plastic connector wasn't holding it in very good. Had to end up replacing the entire unit, but it wasn't very expensive. Between $10-20 if I remember right.

 

[Gary Allan]

The temp sensor on the 4.0 is on the thermostat housing on the Wranglers. I assume so on the Cherokees. It's a 3/8" NPT connection and is integrated with the bypass port that your heater hose is connected to.

You can sorta see it here. It's at a right angle to the rad hose port (about 2 o'clock). The heater hose/bypass port is parallel to the rad hose port.

 

[NYEngineer]

I had a Ford van that the temp guage would go completely down while I was driving. Then, if I went over a big bump, it came back on. It also came back if I whacked the dash. It turned out to be a bad dash ground.

 

[Brandon]

Unplugged and re-plugged the connector a few times and that seemed to clean the contacts. Has been working normal yesterday afternoon and during my drive into work this morning.

Now if I can only fix my gas guage....that gas needle keeps dropping to empty then back up to where it was every so often even when the tank is full.

 

[Gary Allan]

There's a TSB for that IIRC. At least (and again) for my Wrangler. It usually happens for us when we start the engine. You'll start it (most of us don't sit there with the key in the ON position without a purpose

) and then a few seconds later, the low fuel light comes on with a "BEEP" and you realize that it's not working. The next starting event usually (every time for us) gets it working again. We just ignore it and know that we're not going to run out of gas before we, A) Get fuel. or B) Cycle the key again.

Again, there's a TSB out for this.

 

[Curious Kid]

OT:
As far as manufacturing, it seems there's so many little simple things that problems are bound to happen. It's kind of ironic, no?

I had a problem with my mother's 240 volvo where the gauge would work, go out, and then fluctuate between blow normal to over heating. It turned out to be the gauge control circuit that dumbs down the gauge readings. It's since been removed and bypassed so what's now displayed is how the sensor signals. Not likely the case with your vehicle from what I've read thus far.

Good luck. I'd just think that for all this time for jeeps being in production, they would have perfected things by now. I still think about a used wrangler now and again however.

Take care.

 

[MarkC]

Quote:

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The temp sensor on the 4.0 is on the thermostat housing on the Wranglers. I assume so on the Cherokees. It's a 3/8" NPT connection and is integrated with the bypass port that your heater hose is connected to.

You can sorta see it here. It's at a right angle to the rad hose port (about 2 o'clock). The heater hose/bypass port is parallel to the rad hose port.

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There's another sensor specifically for the gauge, it's located back near the firewall near the rear of the valve cover.

 

[Chris142]

Quote:

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There's another sensor specifically for the gauge, it's located back near the firewall near the rear of the valve cover.

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Thats what I was gonna say! The one on the stat housing sends info to the puter and the one on the dr side of the head near the back is for the guage.