aftermarket temp gauge not reading accurately.

I installed an Autometer electric trans temp gauge on my Tacoma. The sender is located in the trans pan. The gauge has been installed for a couple of years or so. But, lately it's been reading higher than the actual temp. For instance, on a cold start up, it would read below 100* and when it warmed up, it would read about 180+. Guage range is 100* - 250*. But, now on cold start up it reads 150+* and when it warmed up it would be pinned at the end of the sweep, which is past 250*. I have replaced the sending unit and gauge with a new one and even bypassed the installed sending wire with another sending wire connecting the gauge and sending unit. It still reads the same. I have checked voltage to the gauge and have ~11.5v. The only thing left I can think of is replace all of the wiring. Anyone have any suggestions?

 

Did you by chance get the wrong sending unit/Defective for the gauge you have ??

Use any sort of non conductive sealer on the sending unit if the sending unit grounds into the pan.

In most cases the resistance increases as the temperature increases anything increasing the resistance will give you the higher readings.

Poor connections poor ground

 

Its the same model unit. As far as I know it isn't defective. I am wondering if it's a grounding issue. It started acting up after my mechanic replaced my motor, flywheel and torque converter. Wondering if something happened then. The sending unit's adapter fitting is welded to the pan. I will pull out the sender and make sure there's sealer around it.