Engine Cooling Fan: 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 within specification, replace thermostat.
NOTE: A pressure tester is used to check both radiator cap and complete cooling system. Test components as follows, following tool manufacturer's instructions.