Thermostat Inspection

NOTICE: Use extreme care and do not damage or scratch the machined aluminum surfaces. Coolant leaks will result.






1. Check the valve opening temperature. Insert a small paper clip or tag wire between the main poppet valve seat and housing. Suspend the thermostat from the paper clip in a pan of water and gradually heat the water. Check the water temperature immediately after the thermostat falls off a tag wire or small paper clip. Replace the thermostat if it does not fall within specifications.

Starts to open temperature:
New: 84-88�C (182-190�F)
Used: 83-89�C (180-192�F)






2. Check full valve opening temperature. Use a pair of calipers and check the distance between thermostat bypass valve and frame when the thermostat is cold. Heat thermostat in water until the main poppet valve fully opens. Measure the distance between the Came and bypass valve. Subtract the valve open reading from the close position measurement. Check water temperatures and measurements to make sure thermostat is opening at the proper temperatures and to the correct lift.

New: 100° C (212° F)
Used: 105° C (222° F)
If the valve opening temperature is not within specification, replace the thermostat.

3. Check the valve lift.

Minimum valve lift:
New: 7.5 mm (0.295 in.)
Used: 6.0 mm (0.236 in.)
If the valve full opening temperature or lift are not within specifications, replace the thermostat.





4. Check that the main poppet and bypass valve springs are tight when the thermostat is fully closed. If necessary, replace the thermostat assembly.

5. Check the main poppet rubber seat. If the rubber is deteriorated, replace the thermostat cartridge.





6. Check the thermostat for leakage around the main poppet and check valves. Install the lower radiator hose on the thermostat housing assembly and fill the hose with clean water. Install a plug with an adapter in the other end of the hose. Place the thermostat in a two quart container and apply five 35.5 kPa (5 psi) of shop air pressure. Measure the amount of leakage from the assembly for five minutes.

Maximum leakage after five minutes:
New: .0.89 L (1.68 pts.)
Used: .0.95 L (2.0 pts.)
If the leakage exceeds specifications, replace the thermostat assembly.