Thermostat Inspection

Fig 1: Testing Thermostat (DO NOT Remove From Housing For Testing)

NOTE: Use extreme care and do not damage or scratch the machined aluminum surfaces. Leaks will result

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
Specifications:
- New - valve opening temperature: 84-88°C (182-190°F)
- Used - valve opening temperature: 83-89°C (180-192°F)

Fig 2: Checking Distance Between Thermostat Bypass Valve And Frame

Check the full valve opening temperature
Use a pair of calipers and check the distance between the thermostat bypass valve and the frame when the thermostat is cold
Heat the thermostat in water until the main poppet valve fully opens
Measure the distance between the frame and bypass valve
Subtract the valve open reading from the close position measurement
Check the water temperatures and measurements to make sure the thermostat is opening at the proper temperatures and to the correct lift.
Specifications:
- New - valve opening temperature: 100°C (212°F)
- Used - valve opening temperature: 105°C (222°F)
If the valve opening temperature is not within the specification, replace the thermostat
Check the valve lift.
Specifications:
- New - minimum valve lift: 7.5 mm (0.295 in)
- Used - minimum valve lift: 6 mm (0.236 in)
If the valve full opening temperature or lift are not within the specifications, replace the thermostat

Fig 3: Checking That Main Poppet And Bypass Valve Springs Are Tight When Thermostat Is Fully Closed

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

Fig 4: Checking Thermostat Leakage

Check the thermostat for leakage around the main poppet and check the 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 5 minutes
Specifications:
- New - maximum leakage after 5 minutes: 0.89 L (1.68 pts.)
- Used - maximum leakage after 5 minutes: 0.95 L (2 pts.)
If the leakage exceeds the specifications, replace the thermostat assembly.