MK 48/14 falsely reading hot

[sandcobra164]

I have an MK 48/14 combo at my house that I attempted to take it its owners house today. The engine coolant temp gauge reads a steady 220 once warmed up and running down the road. The transmission oil temp gauge reads around 230 and creeps up to roughly 270 before I finally lose my nerve and pull over to allow for some cool down time. Hard to verify as there is a small space of movement between 230 and 320 on the gauge. While waiting, I disconnected the fan solenoid so the hydraulic motor for the fan would run constantly to help alleviate my percieved issues. All fluid levels were in tolerance so we made a few cooldown stops and limped home. Once home, I took a water hose and flooded the outside top of the radiator to help cooldown. At the time, the engine was still showing 220 and the trans around 250. The engine temp never dropped but the trans dropped to 215. Left it idling and walked to the house to get my thermometers to do some probing. I took the radiator cap off and inserted a thermometer probe into the header tank. Only reading 165 there. Used my infrared I shot around different components. Highest I found was the trans filter behind the hydraulic tank. It was at 210 to 215 but the trans pan itself was 190. I am thinking the filter is plumbed in series to the cooler so that may not be too bad.

Now onto the question. This truck is a recent rebuild. Does anyone else have a rebuild that is exhibiting similar symptoms? I performed the gauge tests outlined in the maintenance manual and they passed. With the sending units unplugged, the signal wires for both gauges have no continuity to ground so there is not a short or even a partial ground affecting the reading. I am curious if there was a batch of bad sending units used during rebuild as I suspect both as being faulty. Any thoughts or suggestions are greatly appreciated. I intend to put it on the road next Saturday and I will bring my thermometers as reassurance. I really do not like faulty gauge readings so I will probably make a few more stops than usual on such a short 220 mile trip but I certainly respect other peoples property and will not risk damaging anything.

Respectfully,
Joseph

 

[Spdracr]

I have recently acquired a MK48/14 and it is a recent rebuild too. I have the same issue on temp. I don't believe it is running that hot but my gauges read what yours do. Did you ever solve your problem? I also have a M977 and does the same thing.

 

[simp5782]

Could try grounding the gauge. Mine would do the same thing. creep up to 230/240 range and sit there and it is 165 at the sending unit on the outside.. Or a bad sending unit. I ran my truck for months without a temp unit. If i suspect i have an issue I stop every 10mins to check temps at 6 different spots. 4 on the engine 2 on the transmission. I do this 3 times then after that I move it up to a half hour and on up. depending on how comfortable I feel. If it gets hot you will notice it in the throttle before the engine ever gets to that point. U will feel it lug compared to it just getting fired up and running.

If you have a thermoprobe just tie it on the water pipe by the thermostat or the intake and run the length of cable if it has it to a spot where you can see it from the cab.

 

[Lukes_deuce]

Just going to give my two cents on gauges, sometimes the sending unit is not properly tuned for the specific application. Ive had gauges read backwards, low and high, due to the sending unit not being calibrated for the current range. Either through voltage or current. There has to be some information on how these sending units work so they can be properly tested. Another thing is to run an after markets gauge, like an autometer or isspro for comparison.

 

[TacticalTruck]

My temp reads high on the HEMTT and even higher if the lights are on. I figured it was a ground problem.

 

[DrillerSurplus]

I remember a couple of threads about high temp readings that seemed wrong and they came up with solutions I as I recall.- I think this was bout two years I think. I'll see if I can find those.