Water temp sender question

[J-440]

Currently I have 2 water temp senders tapped into the same location after the thermostat. The sender for my FAST ECU reads correctly but the sender for my dash gauge is about 50 degrees lower. I even removed the sender and tested it, put thread locker compound (tape is a no no) on it, then ran the car for 15 min and got the same readings. What gives?
Also, I have a 195 degree t-stat. Which radiator cap pressure should go with it? Thanks again.

[Vegas 69]

Is the gauge sender matched to the gauge?

[J-440]

Yes, everything was bought in a kit.

[68Cuda440]

Dash / gauge voltage is correct?

[J-440]

Yes, voltage is around 13.5.

[MonzaRacer]

Thread locker? Uh no, and why would thread tape be a no no? Unless the sender says it grounds through the threads which would mean you have a ground issue. But if its a two wire sensor then it doesnt matter what you slather on the threads.
Never had any issues with thread tape on sensors for last 30 years, but then rarely see one that grounds through the block.
Are they the same connector? Try swapping them if so.

[MonzaRacer]

Oh and radiator cap has nothing to do with the thermostat. The thermostat opens and closes to maintain engine temperature. The Radiator cap maintains pressure on the cooling system there by raising the boiling point of the coolant.
Every 1 pound of pressure raises boiling point 3 degrees at sea level.
Sea level boiling point is 212F Deg .
4 lb=224
7 lb=233
13 lb=251
15 lb=257
Now most cars with electric fans since advent of fuel injection have turned fans on anywhere from 220F to 235F and generally turn off at around 200F give or take a few degree.
The reason for higher fan temps is emissions, fuel economy and for the fact of the more temp range you have to reject heat to the more heat you can remove.
One thing that came to mind is theat the coolant flow runs slightly different in either position. Otherwise if possible , like connectors are same swap the plugs and see if things read different. If sensors are different that might be issue.