Temp sensor location

[G-Fish]

The engine is a 1974 360.
After 40 minutes of "spirited" driving.

Autometer mechanical gauge in the water pump right next to the bypass hose reads 180 degrees.
FI Tech sensor in the intake manifold reads 200 degrees.
Cheap Craftsman heat gun reads 190 degrees when pointed at the top of the factory 22" radiator.

Is the water temp really that different at those locations, or are one or more of these sensors suspect?

 

[Demonic]

They will never be identical. Different sensor types and size - mech is a capillary tube, FI Tech might be a thermocouple. IR will have emmisivity loss through the brass - it is the surface temp, and the surface is losing heat rapidly. I'd forget about the radiator reading, too far from the heat source. A 10 deg span over the whole sensor range, if they have a 200 deg range it's 5%.
If you want to compare precisely, you'll need the same type sensor in each spot.

Morgan
(calibrated T/C and RTD instruments for a living)

 

[G-Fish]

They will never be identical. Different sensor types and size - mech is a capillary tube, FI Tech might be a thermocouple. IR will have emmisivity loss through the brass - it is the surface temp, and the surface is losing heat rapidly. I'd forget about the radiator reading, too far from the heat source. A 10 deg span over the whole sensor range, if they have a 200 deg range it's 5%.
If you want to compare precisely, you'll need the same type sensor in each spot.

Morgan
(calibrated T/C and RTD instruments for a living)

Thank you.