Thermostat Test: Insight

To test a closed thermostat, suspend thermostat in container of water so that thermostat does not touch bottom of container. Place thermometer in water without it touching the bottom or sides of container, and heat water. Check temperature at which thermostat first opens and then when thermostat is fully open. Measure lift height of thermostat when it fully opens. Lift height should be greater than .31" (8.0 mm) when thermostat is fully open. Thermostat should begin to open when coolant temperature is 187-194°F (86-90°C). Thermostat should be fully open at 212°F (100°C). Replace thermostat if it does not meet specifications.