Coolant Temps Differ

[438wStang]

I went ahead and got the Standard Motor Products CTS that was suggested and tried that in place of the Holley CTS, and made sure to thread it in so I know for sure the probe is in the coolant. But after warming the car up again yesterday, the temps still differed 15° from my Auto Meter gauge (always trusted) to the Holley ECU reading. I think I should be offsetting the sensor, because by the time the reading of the ECU hits 185° for my first fan to come on, the engine is already seeing temps of 195°-200° on the Auto Meter gauge. Thoughts?

[81 TransAm]

Where is the sensor for the Auto Meter gauge? If it's in the head, it will read higher.

[438wStang]

It's a SBF, Super Victor intake, both probes are in the front of the intake. Auto Meter is behind thermostat pass side, Holley is driver side.

[Gaz64]

Is the Auto Meter an electronic stepper motor gauge?

[438wStang]

Nope, just an ordinary mechanical gauge. It's never failed me before, that's why I'm questioning the accuracy of the other sensor.

[BoostedCP]

I found that my trusty mechanical Auto Meter gauge is off 19°. I used two thermometers in the radiator cap opening. Compared those two, the sensor for the ECU, ambient temp laying on manifold (in the shop first thing in the morning) and my mechanical gauge. Turned on water pump let it run to compare the five readings. Four were within 2°. My opinion through years of use the mechanical gauges seem to read high from mostly bad grounds, and the capillary tube providing ground to the engine. I have been involved with three cars this has been the case in.

[Gaz64]

My previous mechanical Auto Meter temp gauge read high if the gauge was exposed to high sunlight temperature. One time it read 120°F when the engine was only about 80°F ambient. 90% of the time it read 180°F-190°F while driving with airflow. Gary

[jb427]

Not only does my Auto Meter temp gauge read 15° high, but my Auto Meter tach reads 150-200 RPM high. Crazy for such a well respected brand!

[438wStang]

I'll try the thermometer trick to see if that works to give me a more accurate reading, then I'll determine which sensor to go off of.