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What's wrong with my temp gauge?

rckymtn

New member
Member
City
Edmond
State
OK
Good morning everyone!

Got a chance to drive the Scrambler a bit and found that the temp gauge did not work. So, following this trouble shoot guide Morris4x4 and a few others, I came up with the following:

Sending unit:
Cold: ~210ohms
~150 degrees: 48ohms (just a quick drive around the block, checked temp with an IR thermometer)

Purple/White wire SU to gauge: 2.7ohms
Gage S to A: 21.00ohms

Jumper voltage: Bounced between ~1.5V & 7.0V

This all seems in spec. I found a 57ohm & 10ohm resistor, so I jumped the S terminal to a ground expecting the needle to move, and nothing.

So, just a bad gauge?

EDIT: Fuel gauge works, though seems to read about 1/4 lower than it should be (F @ full tank, 1/2 @ ~3/4 tank)

Thank you in advanced for your help!
 
Last edited:

walkerhoundvm

Just trying to stay upright
Lifetime Member
City
Cave Creek
State
AZ
What's your fuel gauge doing? In my experience, the fuel gauge tends to go first, which tends to cause problems with the temp gauge since it depends on the fuel gauge feed for...voltage, I think? I can't recall.
 

rckymtn

New member
Member
City
Edmond
State
OK
Fuel gauge is working just fine, though seems to be erring on the side of caution. Reading about 1/4 over what it should be (1/2 tank on the gauge but only took 4 gal at the pump).
 

John N

Addicted....Ex-SOA VP
BENEFACTOR
Gold Member
Lifetime Member
SOA Member
City
Rockville
State
VA
Mine stopping working a couple of months ago, I’m not really sure exactly when. I’m trying a new sending unit first, it was only $5.99 at NAPA and easy to get to.
 

Interceptor

My toy of joy
Member
City
Galivants Ferry
State
SC
Are the gas and temperature gauge easy to replace. They seem cheap enough to buy? Both of mine are goofy. Do people R/R those gauges or just replace complete unit?
 

walkerhoundvm

Just trying to stay upright
Lifetime Member
City
Cave Creek
State
AZ
Not exactly easy, but not the hardest thing to do. Plenty of swearing involved, though.

They can be tricky to work on, ground faults are an easy mistake to make.

Problem is, the aftermarket replacements are terrible. If I ever need to replace mine again, I'll just go with a Speedhut replacement speedo. Not as cool as OEM, but new tech, easy to troubleshoot, and they just work.

You could try buying an OEM speedo off of ebay, but it's a real crap shoot whether the gauges work or not - probably less than 50:50. You might get lucky, you might just find yourself in a wild goose chase.

I might have a spare temp gauge I'd be happy to send for shipping. Let me know and I'll check.
 

walkerhoundvm

Just trying to stay upright
Lifetime Member
City
Cave Creek
State
AZ
I do have a spare - working condition unknown but i can un some resistance tests if need be?
 

Interceptor

My toy of joy
Member
City
Galivants Ferry
State
SC
Still in the thinking stages, with a plan of exactly what I want my Jeep to be at the end. Gauges are livable at this stage.
 

walkerhoundvm

Just trying to stay upright
Lifetime Member
City
Cave Creek
State
AZ
Still in the thinking stages, with a plan of exactly what I want my Jeep to be at the end. Gauges are livable at this stage.
No problem. It's sitting on a shelf in my garage if you decide to go that direction. Resistance is 21ohms, and I have a spare jumper as well. (y)
 

MomoJeep

Basic User
Member
City
Seattle
State
WA
I have a similar problem. The temp gauge reads WAY low, and since it started reading low, now the fuel gauge also seems to read a bit low. Hmmm
 

Jeep Addict

Scrambler Junkie
Lifetime Member
City
Baton Rouge
State
La
I’m having the same problems. Gauges are working oem so about to change both sending units and see what happens.
 

MomoJeep

Basic User
Member
City
Seattle
State
WA
In my case it’s not the sending unit. I checked them. I went ahead and changed the temperature sending unit even though it checked out good, but sure enough that was not the problem. IIRC, There is a voltage regulator involved with the gauges. They operate in the range of 0 to 5V not 0 to 12V so the regulator is needed. If the regular is not working right it seems both gauges it would be effected. That’s my suspicion…
 

Chamba

Not obsessed: focused.
Member
SOA Member
City
Vero Beach
State
FL
Look up Dave the Sparky's threads and you'll be blown away by his attention to detail as addresses exactly this.
 

MomoJeep

Basic User
Member
City
Seattle
State
WA
Look up Dave the Sparky's threads and you'll be blown away by his attention to detail as addresses exactly this.
Wow, this goes beyond my bandwidth for messing with electrical stuff!

Here's what I wish: If Crown/Omix stuff doesn't last, why doesn't somebody just make a quality oem gauge!? I'd be happy to pay more for quality!

But since that probably won't happen, how about this. Can someone pinpoint why these aftermarket gauges fail so easily and find a way to improve them.?! For example, I've taken them apart before and there is what appears to be a resistance wire wrapped around a little flat surface. If they are using a crappy little wire for this, and it is the primary failure point, can we unwind it and solder in a better one ourselves?!?!
 

FLCJ8

Legacy Registered User
City
Palm Bay
State
FL
Wow, this goes beyond my bandwidth for messing with electrical stuff!
Maybe something like this:

 

MomoJeep

Basic User
Member
City
Seattle
State
WA
So is the conclusion that the voltage regulator is the "weak link", the primary failure component? The reason I ask is that the previous time I had a gauge fail it was the wrapped resistance wire that failed...
 
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