92_comanche

This happend a week ago but my temp gauge will not show the tempature the engine is running at. When I start up the MJ the gauge moves from left pegged all the way over to peg at the right then back down to the left. I am sure that the gauge works and one of the sensors is bad or I have a wire issue. THe MJ is a 1992 and I only know about two coolant sensors. The first sensor is the coolant tempature sensor that plugs into the thermistate housing. The second sensor is the Temperature sending unit sensor. Are there any other sensors for the coolant system that I am missing? Latter today I am going to test the Temperature sending unit sensor with my Multi Meter. I replaced the Thermistate roughly two months ago.

93XJLI

its def the sender, im fairly sure its the one on the back of the head that reads temp to the gauge. like you said, check and replace.

92_comanche

Just got back from checking the temp sensor. I found out that the wire from the temp gauge conector to the gauge is good. It was reading 13.7 volts at points tested. I Also found out that the base of the temp gauge sensor is cracked. I will replace this sensor next week and give you an update.

alcratin

I too have the same problem you are describing, did your solution work? or was it something else?

Crazy4x4Chick

Same thing happening to me, although I have already replaced the Temp. Sending sensor twice! Still not working.... Help!

coyote121403

Having the same issue after replacing the head.

alcratin

I had to replace the Coolant Temp Sensor and the Temp Sending Unit. Then it worked.

I had to update this posting as it got a lot of hits as other people have the same issue.

Oh, you better drain your coolant first before you do this, it's kind of like pulling a plug on the bottom of a boat while it's in the water. You better be quick or you'll have a mess.

If you're wondering where is the TSU, it's at the far back of the engine behind the manifold by the firewall. It's a pain to get to. Haynes and Chilton say it's "at the rear left of the manifold". They're semi right. To get it out, you will need a crow foot wrench. A stubby wrench, pliers or even small hands (my wife volunteered to help even) won't do, there are too many other things in the way, not to mention it appears to be snug in a corner against the manifold.

I guess if you're a pro and you like taking your engine apart and you're ok doing that, the best way to get to this thing is to remove the manifold housing and all the other wires and tubes and sensors along with it. Then you should be able to get at it no problem.

You'll need to unbolt the air sensor bracket to move it out of the way and rotate one of the other sensors on the wire harness. Even then you'll still be at a slight angle to get to the TSU. You can't use a Extension for your Wrench because the socket isn't deep enough to get to the nut because the plastic connector is too long. Mine was dead so I broke it off because I knew I had to replace it. The original had a hex of 1/2", the replacement had a hex of 9/16" (in case you are wondering). When I went to put the new one in I struggled with my goliath hands until I just went online and did some research ended up going to Sears where the guy told me I needed a Crows Foot Wrench, they don't sell them individually anymore, but they sell them in a pack (oh goody). Crows Feet Wrench pack is $49. (ugh). If you're on a budget like me, Harbor Freight across the street had them for $9.99 (cheaper, yes, worse tools, yes. I know) Anyway. Use a Driver Extension (12" pref) and then you have to eek it in 1/4" turn at a time till it's on tight. Then snap the sensor cable back on and you're back in the game.

If you're like me and you also replaced the CTS, the BWD (from Pep Boys) replacement part had a longer shaft than the original, so you'll need to experiment with how far down you need to screw the darn thing in to get it to trigger the fan at 205 - 210 degrees. This will take you several hours as you'll need to fire up the engine and monitor the temp gauge and listen for the fan to come on, if it doesn't come on at 210, then watch when it does, stop the engine. Let it cool down, ratchet the CTS down 1/4 - 1/2 turn and try again till you get it right.

If you're like me just trying to save a buck to avoid a car payment, while the sun is in the sky, I'll do it the hard way to keep myself out of bigger trouble as I'm not a mechanic. Computer problems and pro audio and midi is my day job. This stuff appears logical enough. Any way hope this helps someone in the future who may be searching for help on this topic.

baloozabub

I had the same problem and seem to have found the fix. I held in my odometer/trip stick while starting engine. This will bring the odo reading to 0000000 then 111111 and so on until 999999. This does a check on all the dash gauges. After doing this my temp reading went back to normal. Hope this helps.

ElColo

Hey All,

Just bought a Cherokee Classic, '98 4 days ago. When I test drove it the temp gauge worked fine. Now it doesn't even budge. I sure I hope can just try that trip/odometer trick and not spend all that time replacing units. That might be a bit over my head. Either way, thanks for the help.

Slick761

That's a trip

ElColo

I just tried this and it didn't work. I didn't get a 0000000, 111111111, or anything. Could you elaborate a little? Do I need to hold it down for 10 seconds or something?

My temp gauge just sits at the bottom without moving. It worked for a second, then dropped again. Is this gauge not working going to have any effect on the cooling system? Or is it just a gauge issue. Please help, look to take a big trip in hot weather over mountain passes this weekend.

Thanks in advance.

90_cherokee

The easiest way to determine if your gauge is working correctly is to take the wire off the sending unit on the rear of the cylinder head.

Using a jumper wire,insert it into the wire that you unplugged frtom the coolant sensor.

Attach the other end of the jumper to a good ground.

Get in the vehicle and turn the key to the "on" position. DO NOT start the vehicle.

Observe the needle on the gauge,if it pegs 260 quickly,t,the gauge is good.

Make sure you turn the key off after making this observation ,leaving it on with the sending unit wire grounded will fry your gauge.

ziegler.1289

If someone happens to read through this thread again. I have X2 on the hold trip button thing. I am unsure if that's the correct way to do it but I had my gauges mess up and I did this and it reset them. Keep in mind this was on a 97-01 XJ. You will know you did it right when it the trip shows all 0,1,2,3,4,5,6,7,8,9's.