Engine Cooling System: Testing: Thermostat
- Visually inspect thermostat for corrosion and proper sealing of valve and seat. If okay, suspend thermostat and thermometer in a 50/50 mixture of coolant and water. See Fig 1. Do not allow thermostat or thermometer to touch bottom of container. Heat water until thermostat just begins to open.
- Read temperature on thermometer. This is the initial opening temperature and should be within specification. Continue heating water until thermostat is fully open and note temperature. This is the fully opened temperature. If either reading is not to specification, replace thermostat.