Cooling System Servicing: Maintenance: Thermostat

Visually inspect thermostat for corrosion and proper sealing of valve and seat. If satisfactory, suspend thermostat and a thermometer in a container with a 50/50 mixture of anti-freeze and water. See Fig 1 .
Do not allow either thermostat or thermometer to touch bottom of container as this concentration of heat could cause an incorrect reading. Heat water until thermostat just begins to open.
Read temperature on thermometer. This is the initial opening temperature and should be within specifications. Continue heating water until thermostat is fully open and note temperature. This is the fully opened temperature. If either reading is outside of specifications, replace thermostat, as it is not adjustable.

Fig 1: Testing Thermostat in Anti-Freeze/Water Solution

NOTE: Support thermometer so it does not touch bottom of container.

NOTE: Chevrolet recommends hanging thermostat in 33% glycol solution at 25°F (4°C) above temperature stamped on thermostat. Valve should open. Remove thermostat from solution and place in similar solution at 10°F (-12°C) below stamped temperature. Valve should close.