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Temp. sender, gauge or thermostat?

G

gba88

NAXJA Forum User
Location
PA
I have an odd problem going on with my coolant gauge. It acts fine (no jumping on startup) until I'm idling in traffic on a hot day. It's usually a little above the 210 mark, but then it will sort of jump into the red area and hang there until I kick the heater on and get moving again. It doesnt' slowly drop though, it sort of jumps again back to a little above the normal area. I'd say it visually jumps about at least 1/8 of an inch, maybe a quarter. It's only from the red to the normal area or vice versa.

Can anyone guess what part is more likely to be at fault considering the circumstances? Originally I thought the sender, but after searching and reading, it seems like if the sender (or the gauge) is going, it would be a lot more erratic or unreliable.

In case it might be related: my oil gauge has been acting up off and on for a couple months, too. When accelerating on the highway it jumps all over the place between the halfway mark and the right hand side.
 
I would check the fans, both the electric and replace the viscous hub. If you have AC, turn it on to see if the electic fan comes on. Check fluid not only in the plastic tank but open the radiator too. Often if there is a leak the plastic tank looks good but there isn't enough coolant in the system.
I assume you have an 1988?
 
Sorry, it's a 96, 231, and about 19x,xxx on the odometer. I know the fan is kicking in for sure, but the ac doesn't work (leak in it somewhere). I don't have any coolant loss, and both the tank and radiator look good (as far as color of the coolant and levels).
 
There is not a good way to check the viscous fan hub. Has it been replaced within the last 5 years? If not, do that next and see if there is improvement.
 
sjx40250 said:
There is not a good way to check the viscous fan hub. Has it been replaced within the last 5 years? If not, do that next and see if there is improvement.
Click to expand...

Def. not replaced by me and I've had it since 2006 so no. Is it a big job or expensive?
 
Physics says that it is impossible for the temperature to jump many degrees in just a second or two. If that is what you mean by jump, then you are fighting an electrical problem such as a loose connection to the sensor or gauge cluster. Other issues can be a bad ground.
 
old_man said:
Physics says that it is impossible for the temperature to jump many degrees in just a second or two. If that is what you mean by jump, then you are fighting an electrical problem such as a loose connection to the sensor or gauge cluster. Other issues can be a bad ground.
Click to expand...

This is why I was leaning more towards the gauge or the sending unit. I'm not sure of the conversion of "1/8 to 1/4" of an inch to degrees, but it definitely drops or rises within seconds. Also, it has never actually overheated even though I've sat with it in the red through many stop lights.
 
It sounds to me like you have a defective sender. They are $14 at autozone so I would just throw in another one.

The only real test for the gauge is (1) disconnect the sender wire and see if the gauge goes to zero, then (2) touch the sender wire to a good ground and see if the gauge pegs out the other direction. If you want to test it more, you can put a variable resistor between the sender wire and ground and see if the gauge moves smoothly.
 
Last edited:
ehall said:
It sounds to me like you have a defective sender. They are $14 at autozone so I would just throw in another one.

The only real test for the gauge is (1) disconnect the sender wire and see if the gauge goes to zero, then (2) touch the sender wire to a good ground and see if the gauge pegs out the other direction. If you want to test it more, you can put a variable resistor between the sender wire and ground and see if the gauge moves smoothly.
Click to expand...


Thanks for the replies! I'm going to see how much give the fan has later after work (saw some stuff about if it moves freely, the clutch is shot). I don't have an autozone, but I think advance has the sender for about 20. I'll post back to the thread if I ever figure it out :)
 
krawler09 said:
Please let us know if that fixed it i'm having sort of the same problem
Click to expand...

No problem. Checked the fan earlier, and it doesn't spin at all by hand (read online somewhere about if it spins at least 5 rotations on it's own, the clutch is worn out). Mine *maybe* moved a couple fins worth when I tried to give it a spin, and felt like it had a lot of resistance. Not sure when I'll pick up the sender, but prob this week someday after work. I really want to figure out what the issue is because even though I know it's not actually overheating (yet anyway), it sucks running the heat on high when it's 90 something out when sitting at a stop light!
 
Hey guys,
I'm finding conflicting info on where the sensor is that ties to the gauge. This is a 1996, so is there just the one sender on the thermostat housing, or does it have one in the rear on the block also? I can't do the obvious (look at it) at the moment so any help would be appreciated. Part number at advance would help even more since I get a 2 wire version and a 1 wire version when I search. I know the one on the housing has 2 wires, so maybe there actually IS another sensor on the 96 in the rear? I'm confused because I saw a post where a guy said that the high output switched to just the one on the thermostat housing.
 
gba88 said:
Hey guys,
I'm finding conflicting info on where the sensor is that ties to the gauge. This is a 1996, so is there just the one sender on the thermostat housing, or does it have one in the rear on the block also? I can't do the obvious (look at it) at the moment so any help would be appreciated. Part number at advance would help even more since I get a 2 wire version and a 1 wire version when I search. I know the one on the housing has 2 wires, so maybe there actually IS another sensor on the 96 in the rear? I'm confused because I saw a post where a guy said that the high output switched to just the one on the thermostat housing.
Click to expand...

Someone correct me if I'm wrong, but I believe the 96 has only one temp sender on the T-stat housing, which feeds the ECU and the Gauge.

Also, if you've decided to replace your sender, I recommend getting a dealership OEM sender. I had trouble with an after-market sender that I got ... it never gave the correct reading. I finally replaced with OEM, and it was immediately correct after that. Here is a good place to get discount prices on dealer parts:

http://moparonlineparts.com/

Good luck.
 
montanaman said:
Someone correct me if I'm wrong, but I believe the 96 has only one temp sender on the T-stat housing, which feeds the ECU and the Gauge.

Also, if you've decided to replace your sender, I recommend getting a dealership OEM sender. I had trouble with an after-market sender that I got ... it never gave the correct reading. I finally replaced with OEM, and it was immediately correct after that. Here is a good place to get discount prices on dealer parts:

http://moparonlineparts.com/

Good luck.
Click to expand...

Thanks for the reply! Maybe I should forget about the one at advance, I saw a post on another site where a guy replaced his original and had the same problem.
 
Yeah ... lots of people have posted problems with after-market temp senders.

Did you run the test that ehall described? I would do that before spending $$. Since your OP gauge is also acting weird, It's possible you have a poor connection at your gauge cluster. Does the OP gauge go nuts at the same time as your Temp gauge? Also, when the OP gauge is having problems, are you sure your crankcase has the proper level of oil in it?
 
ehall said:
you should have a separate sender at the back of the head, in the corner nearest the driver, beside the valve cover
Click to expand...

On a '96? I thought the last year for that was '91. 1991 was a transition year ... the first year with the HO motor, but still had 2 temp senders.
 
Last edited:
montanaman said:
Yeah ... lots of people have posted problems with after-market temp senders.

Did you run the test that ehall described? I would do that before spending $$. Since your OP gauge is also acting weird, It's possible you have a poor connection at your gauge cluster. Does the OP gauge go nuts at the same time as your Temp gauge? Also, when the OP gauge is having problems, are you sure your crankcase has the proper level of oil in it?
Click to expand...

Haven't tried the test because I wasn't sure which sensor to check. The mopar site only listed 2 senders one was for with gauge and one was for without. The op activity did not happen at the same time, but the oil level was fine. I keep a real good watch on my fluid levels. I see from the other post that I should check the one on the head so I guess I'll see if I can locate that next. I kind of looked real quick earlier on my break but didn't see it standing out in the rear driver area of the block. Will have to take a better look I guess. Might be covered in dirt and grease :)
 
gba88 said:
I see from the other post that I should check the one on the head so I guess I'll see if I can locate that next.
Click to expand...

If you have it, it will be on the very back of the head, driver's side. You'll see the wire going to it. it points right up out of the head.

I went through a lot of this on my '91 xj when I swapped my cluster from idiot lights to gauges.
 
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