Cummins/Onan — Checking accuracy of high-water-temperature cut-off switch
Testing & diagnosis
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Procedure
- Remove the radiator cap and insert the bulb of a Fahrenheit thermometer in the radiator water.
- Set the dial at 220 degrees.
- Cover the radiator and operate the engine until water temperature exceeds 180 F.
- Slowly turn the dial counterclockwise until the ignition is switched off.
- Dial reading should then coincide with the thermometer reading.
Tools required
- Fahrenheit thermometer Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Cut-off approximately 260 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.