thermostat question

[leanburn]

 ive been haveing an issue with my coolant temps. i have the fast efi setup wich allows you to adjust the fan kick on temp. i have the sensor for the fan in a 3/8 hole on the driver side of the thermostat, my dash guage is in the factory 1/8 hole on the passenger side. problem im having is there seems to be a 10 degree diffrence between the two. i used a heat gun to double check and it confirms a 10 degree difference. why would this be?
 

[burdar]

The original gauges are 40 years old and probably aren't that accurate.  Have you had your gauges rebuilt and calibrated?  It's also possible that you have the wrong temp sender for the original gauge.  That could make it read wrong.

[Chryco Psycho]

Some glitch in the water flow inside the engine , either the water is restricted leaving one side coming out of the engne causing the cool water to move slower into that side or there is a restriction into the warmer side , or more sludge buildup