Cummins/Onan — Testing the Thermostat
Testing & diagnosis
From a Cummins/Onan service manual — check it applies to your exact model before use.
Browse Cummins/Onan generators & specs →
Procedure
- Remove thermostat from cylinder head.
- Heat a pan of water to approximately 150°F and check with an immersed thermometer.
- Suspend thermostat in 150°F water; it should start to open.
- After it opens completely, remove it and let it cool; it should close within a short time.
- Replace if it sticks or does not operate properly and always install a new gasket.
Tools required
- Thermometer Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Thermostat opens at 150°F ± 20°F
Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.