Part Deux: Temp sensor/sender location

[bobby v]

This is a follow up to thread I posted earlier
https://www.gmt400.com/threads/temp-sending-sensor-locations.49362/
Ok, I have since borrowed from my cuz a cool testing tool for coolant temps with the motor running, it consists of a radiator cap that has a rubber type plug that you insert a thermometer in to the small tight hole that looks like a meat thermometer, about 8" long.
I installed it and started the truck watching it thru its warm up till full operating temp with a/c on.
Wont bore you with all the different readings but in general there was about a 25' diference between my in cab gauge and the testing unit, which we seem to agree that its the location of the sending unit that causes this. At full read out it was 195' vs 220'
So heres my question, which temp should I believe is the true operating temp, the testing unit, or the sending unit (higher reading). I do believe that the sending unit being in the head and between two header primaries is picking up some of that heat thru transference.
Am I correct, what say you gurus. I sure don't want to blow a head gasket on my new motor
Thanks as always
Bobby V
PS There is a bung/port beside the coolant outlet in the intake manifold that I could move the sending unit to but would i only be fooling myself into believing a more favorable temp and ignoring the other one?????

 

[Schurkey]

If you have a cross-flow radiator, the rad cap--and therefore your thermometer--is on the COLD side of the radiator. You're reading the temperature of the "cooled" coolant, ready to be pulled back into the water pump and sent through the engine again.

Obviously, the temperature on the HOT side will be higher.

The important part is WHAT TEMPERATURE DOES THE COMPUTER REGISTER when you check the CTS with your scan tool?

The engine is in no real danger until 240--260 degrees. The "HOT" light didn't come on until the coolant was that warm on older vehicles.

 

[alpinecrick]

The port by thermostat housing is for the temp sending unit for the computer.
As Schurkey says it’s the temp your scanner is reading from the computer that counts.