Engine Cooling Systems: 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 (AMC recommends 100% anti-freeze). 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.
NOTE:
AMC recommends placing a.003" feeler gauge between thermostat valve and seat. When valve begins to open, feeler gauge will slip out easily.
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.
NOTE:
Chevrolet recommends hanging thermostat in 33% solution at 25° above temperature stamped on thermostat valve, agitating solution to distribute heat; valve should open. Remove thermostat from solution and place in similar solution at 10° below stamped temperature; valve should close.