Well....I installed a NEW water temp sending unit, and a different temp gauge. still nothing changes. so I guess it must be the wiring....I don't know how to test this. anyone help me here??
I am driving along with the vehicle all warmed up and I noticed that the engine seems to be running on the cool side. I replaced the thermostat. no help. I replaced the sending unit...no help. I replaced the temp gauge...no help. Once in awhile it would go up to the 1/2 way mark and go down and up just a little bit indicating the opening and closing of the thermostat, then it drops all the way down to the left...like a cold motor. Now it seems like it is parked there....but.....I wouldn't bet the farm it will stay there...it may come back up for a little bit then go back into hibernation. I rigged up a mirror so I can watch the gauge with the engine running and I wiggled the wiring harness and no change at all. Any ideas???

 

Honestly sounds like a bad thermostat. Did you use a Cummins thermostat?

If you have a multimeter you can probe the ends of the sender unit wiring for continuity, and pull the dash and check the gauge the same way.

 

no...no cummins 'stat.... It is doing the same thing as with the original one was.

 

OK.. I unplug the sending unit... and simply check for continuity across the plug's connectors??

 

Yes. Should run current thru the gauge and back if wires are good.

Have read a lot of posts regarding not using a genny Cummins stat and usually that is a problem...

 

DMM reveals continuity......
I guess the only thing left is to replace the sending unit ....again???

 

Is there any chance you know someone who has an Edge Insight? If so and they will let you borrow it, you can use it to tell you what the ECM thinks the engine temp is. That will at least let you rule out a problem with your dash/gauge.

 

Im wondering if the temp sending unit is the same for a 1997 vs a 96
I did have a different motor put in and have had the trouble ever since.

 

Regardless, get the CPL off the engine tag and get the Cummins sending unit, if you narrow it down to a sender.

 

Im not familiar with what a CPL is...Mine is a 97...so wont have much of a computer if any at all.
where do you go to get cummins parts??? get the P/N and go to a tractor dealer??

 

Could it be as simple as this?

When these trucks were sold new the dealer was supposed to tell the new owner the following and a sheet came with the owner's manual that said:

NOTE: THE COOLING SYSTEM USED ON THE CUMMINS DIESEL ENGINE EQUIPPED VEHICLES PROVIDES THE CAPACITY AND PROTECTION OF THE HIGHER GVWR AND GCWR RATINGS AVAILABLE ON THESE VEHICLES. OWNERS SHOULD BE ADVISED OF THE NORMAL SLOWER WARM UP AND LOWER ENGINE OPERATING TEMPERATURES ASSOCIATED WITH DIESEL ENGINES.

THE COOLANT TEMPERATURE GAUGE WILL FLUCTUATE ON DIESEL ENGINE EQUIPPED VEHICLES. IT IS INFLUENCED BY VEHICLE LOAD, OUTSIDE AMBIENT TEMPERATURE AND EXTENDED IDLE TIME. THIS FUNCTION IS CONSIDERED NORMAL

GAUGE FLUCTUATION WILL BE NOTICED MOST OFTEN UNDER STEADY STATE (HIGHWAY) DRIVING.
PLEASE ENSURE THAT YOUR CUSTOMER IS AWARE OF THIS NOTE PRIOR TO RELEASING THE VEHICLE.

In 1998 after years of complaints Cummins electronically turned the coolant gauge into basically an idiot light.
The temp still fluctuates, you just can't see it.

 

Im going to have to back off on the meds....
I was looking at the air INTAKE temp sewnsor and not the coolant temp sensor. I knew this too! Just forgot. Anyways...the problem is when they swapped the motors the wrench must have accidently broke the sending unit ..the spade terminal comes out of the sender...I stuck it back in and the gauge works perfectly... I have a new sender ordered....
jeeps I feel like an old fart.