Engine Temp Gage stays at 0 (zero)

[Mt Doom Field Owner]

Me again... new-bee... bought my first M35A2 a couple of weeks ago and the SS Forums are my saviour! Three of four questions or issues I have posted here were answered in minutes to hours but not DAYS! as I have found in other forums. This is a powerful MV owners forum. My issue now... a dead engine temp gage. I swear I looked through the TM-s and I swear I tried the search features best I could on the forum but only found what to do if you have high engine temps on the gage... i.e. engine running hot. My cooling system is full of antifreeze and the truck runs like a charm and doesn't run hot... the gage is just dead. Can someone tell me the manual # that addresses the temp gage instrument itself in the test proceedures? Or where to start multimeter tests on the wiring harness and such to see if it's the gage or the harness or someplace else? I'm taking the deuce to a local truck stop near my house to have a wheel cylinder replaced by a knowledgable 2.5 ton mechanic so I may get him to look at this gage for me as well. Anyone got a lead on a new/used gage if it is the problem? Or if you've gone through this problem and fixed it in your early stages of ownership please offer any advise you can. Of all the gages on this thing I believe the engine temp gage might be the most vital. Thanks for your help guys! Love the SS Forums!!!

 

[dmetalmiki]

temp problem

Well I got so fed up with the indescriminate readings of electrical gauges I have changed ALL the temp guages in my trucks to capilary type. "ah-la" jeep etc. NOW what I see is what i have! great mind easing convo. on the subject of gauges I have mine on easy "scan" top = left to right oil engine then air pressure (brakes) below right to left temp engine then batt then (who cares! ((its free!!)) fuel!)

 

[Mt Doom Field Owner]

I had a chance to allow an oil drilling company to set up a drilling rig and pump station on my property with a 5 year contract for a couple of grand but declined... I might be sitting on a life-time supply of crude oil or natural gas... just 2000 feet deep! Wonder if they would have let me tap into their storage tank?? Guess I will just have to buy my fuel for now.

 

[Wolf.Dose]

For your temp gauges problems I have the following ideas:
First: Did you check the harness for propper contact? Old harneses sometimes have broken cables inside due to their age.
Second: Is the sending unit doing its job? The manuals should have told you which one it is and where it is located. The registor reading must be different between a cold and a warm engine. But readings below 120 F are not shown on the gauge.
Third: Is the gauge in propper order? Are the contacts not mixed up (If plus and minus is interchanged, there will be no reading.).
After this the gauge should read something usefull.
Wolf

 

[Jinx]

My temp gauge sticks a little. After the truck warms up, it just springs to about 140 degrees then will slowly raise to normal operating temperature. I can some times coax the gauge to respond sooner by tapping the gauge glass.

 

[Larch]

If you found the sending unit (on the passenger side near the front of the motor). You can do a test to see if it is thew sending unit or the gauge. While the truck is running remove the wire from the sending unit and ground it out(touch the motor with the exposed wire). If the gauge maxes out (goes all the way to the right) then you have a bad sending unit. If it does nothing you may want to check the wire connections to the gauge. Good luck.

 

[Mt Doom Field Owner]

Outstanding! I can do these things myself and get a pretty good idea if it's the sending unit or wiring or the gage. Only it's dark out there now I will have something I can try in the bright morning light! (I don't really like working with my flashlight)... that's the nice thing about my MV... it is just sitting there waiting for me to play with it.!!!

 

[kastein]

I know this is a year old, but in case anyone else runs into the same thing...

- first find the temp sender (on my LDS-465 it's located on the passenger side of the front end of the intake manifold log) and measure its resistance with a multimeter. A few minutes after shutdown I found that mine was in the 1.7 to 1.8 kilohm range, and going up (i.e. negative temperature coefficient.) If yours is shorted, or open, replace it.
- now disconnect the cable from it (it should be circuit 33 if it is like a 5 ton, which I believe to be true) and disconnect the same circuit from the gauge on the back of the IP. Measure resistance from end to end on this wire, it should be a few ohms or less. Try shaking the wire and flexing the wiring harness if it is not, when the resistance fluctuates you are near the problem. A meter with a continuity beeper is a great help here. Fortunately my wiring harness was fine. Once you have verified this:
- plug the sender end of the cable back in but not the gauge end. Measure resistance from the loose end of circuit 33 (i.e. at the gauge end) to ground. Should be (by now) a little higher than the last value you measured directly at the sensor, since the engine is still cooling down. If it is an open circuit you have a flakey connector somewhere, probably the one for the sensor.
- plug circuit 33 back into the gauge. Mine was plugged into the passenger side pin, yours probably should be too.
- if the gauge does not work now, unplug and reconnect the other plug on the gauge, which should be the power source. It should measure (I believe) 24 volts or so. If it doesn't, your problem is upstream of the gauge OR your gauge is bad AND your power feed to it is bad.

I ended up spending $39 on this: Temperature Gauge 120-240 F, MS24543-2 and it works quite nicely. It is not exactly identical to original stock units so if you are restoring the vehicle find something else, but works for anything other than picky restorations. I have a used unit coming in the mail from one of the guys on here should I ever decide to restore mine fully.

 

[clinto]

Kastein, that's a heck of a well written walkthrough for gauge troubleshooting. Much thanks!

 

[kastein]

No problem... I'm an EE by trade, messing with wires and junk comes naturally hope it helps someone, if it does it was worth typing up.

 

[progun]

My guage reads pegged all the time after it warms up. Maybe we could meet in the middle!

 

[wbdodgeiv]

I'll have to try those idea's as well, I too have a dead temp gauge. Then again, I haven't taken the thermostat from the glove box and reinstalled it after the previous owner took it out for a reason he forgot

 

[Heavysteven]

Replace the gauge and sending unit. That's what I do and it's worked every time.

 

[kastein]

My guage reads pegged all the time after it warms up. Maybe we could meet in the middle!

You probably have a bad gauge or a short circuit somewhere in your wiring harness (temp sender is NTC, negative temperature coefficient, so resistance goes down as temp goes up.)

I always prefer to test my way to the solution instead of throwing parts (unless I have not yet learned how a specific subsystem works, then I throw parts like I own stock in their manufacturer!) at the problem, it is far cheaper though it does take a bit longer.