Coolant Temperature Gauge

The coolant temperature gauge circuit reads the engine coolant temperature through the use of an engine mounted coolant temperature sensor (thermistor). The voltage is sent from the fuse block through the instrument cluster to the coolant temperature sensor (thermistor) and to ground. As coolant temperature increases the thermistor resistance decreases, and when the coolant temperature decreases the thermistor resistance increases. The display of the correct temperature reading is dampened slightly upon start-up (cycling of ignition) and will stabilize after approximately 12 seconds. The sensor resistance range is from 320 ohms at 50°C to 36 ohms at 130°C.

When the ignition is returned to the OFF position the coolant temperature gauge moves the pointer to the mechanical zero position or C. If any time a coolant temperature sensor error is recognized for more than 8 seconds by the gauge, the pointer will return to C. If the sensor signal is then recognized as being intact for more than 4 seconds the gauge will resume operation as in a start-up (cycling of ignition) mode. This takes approximately 12 seconds in order to stabilize.

The coolant temperature gauge provides an accurate readout with operating voltage anywhere between 9-16 volts. The coolant temperature gauge accuracy tolerance is accurate within 4.4 degrees of needle sweep. The gauge can also tolerate a 24 volt over voltage situation for up to 60 seconds and a reverse battery voltage situation of -12 volts for 60 seconds with no lasting damage to the unit.