CONTROL GP-TRANSMISSION 2995839 - Caterpillar

In many applications, the accuracy of the temperature contactor used in an alarm or shutoff system is very important. To accurately check the actuation temperature of a contactor, do not use a static water bath. Actuation temperature will be 10°C (18°F) or above the actual actuation point when the contactor is installed in an engine. Even using an agitated glycol bath can produce a 3 to 5°C (5 to 9°F) error.
In order to provide a rate of coolant flow high enough to insure accuracy, contactors should be checked in a running engine in a location with good coolant flow. Refer to the test procedure described in the reference.