minor temp gauge problem

[mjeff87]

One tiny problem with the full gauge cluster I swapped in last week....the temp gauge is reading too high, like 260 degrees when fully warmed up. All other gauges work fine, BTW. I pulled the cluster from a 90 MJ (non-HO so the wiring has the same polarity), 4.0L, and grabbed both the oil and temp sending units and swapped them onto my 2.5L. With the 4.0 sensor, the gauge read from 160 to 240, so I ponied up and bought a new sending unit and put it in yesterday. Now it reads 180 to 260 (almost pegged)....

 

Also, when starting up, the needle pegs waaaayy past 260 while cranking, then drops back to 180-ish when it starts. By comparison, the OP gauge zeros itself with key-on, then springs right up to 60-65 psi when started and running.

 

I did pull the plastic bezel off the cluster and cleaned all the gauge faces carefully when I got it....I'm thinking I may have futzed the needle on the temp gauge accidentally. I've got a heat gun here at work to borow tonight and see what the actual temp really is when hot, then maybe pull the bezel off and push the needle a bit to match.

 

For those of you with gauges, what does your temp gauge do when you hit the key, sweep far right, far left, or not move at all?

 

Jeff

 

edit: you can watch and see when the tstat opens, so I know everything's working like it's supposed to. Just seems like the gauge is registering about 40-60 degrees too high.

[87manche]

mine sweeps to the right when cranking, it will hit about 260.

 

as soon as the starter is released it pops back down to the left.

 

sounds to me like you've got a bit more resistance than you should have in the circuit, and that would cause it to read high.

[mjeff87]

When mine sweeps right, it goes way right, like to about the 3 o'clock position :cry:

[fiatslug87]

I might have an extra temp gauge you can have, I'll check tonight after work and let you know.

[87manche]

When mine sweeps right, it goes way right, like to about the 3 o'clock position :cry:

i'm sure mine would as well, but the jeep starts before then.

[Oizarod115]

mine goes right to the screw at almost 3' before it goes back down

[CWLONGSHOT]

Mine sweeps to the max and after engine starts reads correct temp.

 

CW

[mjeff87]

This is where it read with the sensor from the junkyard. I just shut it off right before I took that pic (not too shabby oil pressure for a 180K 2.5L, eh?)

With the brand spankin' new sensor it floates up about 1/2 way into the red (actually made it worse). I guess the sweep right is normal, then?

 

I've got the heat gun...gonna get a real read tonite after work.

 

Jeff

 

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[Oizarod115]

any chance you've been cookin that engine and just didnt know it?

 

my 4.0 ran at 250 for MONTHS and months before i figured out it awsnt a bad gauge. that engine has to hate me... but it still picks up nice

[mjeff87]

No, but I was starting to think that....

 

I put the heat gun on it this morning after a 30 min drive into the office. Upper radiator temp is about 180-185, and the head right where the sensor screws in is running 195-200. I tried to get a reading on the lower rad hose but couldn't get an accurate one. Lots of spinny things in the way and I have good clothes on :D

 

Think I'll put the old sensor back in, and maybe try to "adjust" the needle on the gauge.

 

Jeff

[tjbliley]

I know it goes against your better judgement, but you could always get a brand new sensor from the parts store. It may send the truck into shock to have new parts but it will only be temporary.

[mjeff87]

LOL Jerry....but that is a new sensor.....$26 friggin' dollars worth.

 

I pulled the idiot light sender and replaced it with a junkyard gauge sender first, then sprung for a new one (which read worse than the junkyard one).

[tjbliley]

That sux. I would say that you need to check the ohms on the sender to see if its in range. if it is adjust the gauge to be correct. if not then you prob got a bad sender.

[87manche]

I would say that the 20 year old wiring harness "may" have a little added resistance due to corrosion.

ohm out the wire to the sender and see what you get.

should be near 0.

[fiatslug87]

I might have an extra temp gauge you can have, I'll check tonight after work and let you know.

I only have the blue temp gauge not the red as in your picture. There are several listings for temp senders in the parts cataloge maybe you have the wrong one?

[mjeff87]

That's very possible, too. The parts guy had two listings for the sender, and the note in the book said "compare to original" He pulled both and we eyeballed them, comparing them to the idiot light sender I had originally and the gauge sender I got from the 'yard, and none of them were the same length so I took the one closest to the idiot light sender. Thanks for the offer on the gauge, though :cheers:

 

Jeff

[HOrnbrod]

Here's a pic of the one you need (# 12), part number 53005309. Maybe they can cross reference it for you.

 

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[mjeff87]

Thanks Don :waving:

[mjeff87]

I would say that the 20 year old wiring harness "may" have a little added resistance due to corrosion.

ohm out the wire to the sender and see what you get.

should be near 0.

 

Mmmmkay....mighta found the problem. I ohmed the sending wire out straight to the neg terminal on the battery and got about 91 ohms (key off).

[HOrnbrod]

I would say that the 20 year old wiring harness "may" have a little added resistance due to corrosion.

ohm out the wire to the sender and see what you get.

should be near 0.

 

Mmmmkay....mighta found the problem. I ohmed the sending wire out straight to the neg terminal on the battery and got about 91 ohms (key off).

 

If I read this right, you're reading through the meter movement and 91 ohms is okay. The simple way is to turn the key on, disconnect the sender, and the gauge should go to C (left). If not, touch the coolant sensor wire to ground, the gauge should go to H (right). If it does both, the sender is bad. If it does not, the sensor wire to the gauge is open. This is for the 91, but I think the temp gauges are the same in all years. I take the same temp sensor as you do.

[87manche]

jeff, I've got a known good temp sender for my 87. I replaced it because I thought the gauge was wrong, turns out my 4.0 really does like to run at 180*.

[mjeff87]

Thanks Nate, but I don't think it's a sending unit problem. Unhooked the wire and keyed it, and the gauge only drops to about 150 degrees. I think I just pushed the needle a bit too far when I was cleaning it. I'm gonna pull the bezel off again and "persuade" the needle a bit.

 

Jeff

[87manche]

yeah, I did the same thing to my fuel gauge when I took it apart to clean it.

 

just needed to be very careful when pushing it back.

[Eagle]

You can check the sender with a multimeter, a pot of water on the range, and a candy thermometer.

 

At 100 degrees, the sender should offer 1365 ohms resistance. At 220 degrees it should be 93.5 ohms. At 260 degrees it should be 55.1 ohms.

 

To my surprise, this applies to all years. I thought they reversed the polarity on the instruments from 1990 to 1991. Turns out they only reversed in on the fuel level sender.

[tjbliley]

Thats good to know. I knew I liked you for some reason Eagle.