Temp sensor location

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)