Cummins/Onan 12.0 RDJC — Testing Thermostat
Testing & diagnosis
For the Cummins/Onan 12.0 RDJC, from the Cummins/Onan operator's manual.
Applies to: Cummins/Onan RDJC
Procedure
- Remove thermostat from cylinder head.
- Heat a pan of water to approximately 150 F (66 C); check with thermometer.
- Suspend thermostat in 150 F (66 C) water; it should start to open.
- Remove from hot water and allow to cool; thermostat should close within a short time.
- Replace thermostat if it sticks or does not operate properly.
- Always install a new gasket when replacing the thermostat.
Tools required
- thermometer Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Opens at 150 F (66 C)
Full service-parts list: Cummins/Onan RDJC →
Source: Cummins/Onan operator's 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.