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Home›Repair guides›Cummins/Onan›Thermostat Test

Cummins/Onan 4MCCK / 605MCCK — Thermostat Test

Testing & diagnosis

For the Cummins/Onan 4MCCK / 605MCCK, from the Cummins/Onan service manual.

Applies to: Cummins/Onan 605MCCK, Cummins/Onan MCCK, Cummins/Onan MCCK engine

Procedure

  1. Place a thermostat and a thermometer in a water bath.
  2. The thermostat should start to open at 145 deg F and be fully open at 165 deg F.
  3. It should close immediately when removed from hot water.
  4. Replace the thermostat if it does not operate properly.

Tools required

Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.

Specs & values

  • Starts to open at 145 deg F
  • Fully open at 165 deg F

Full service-parts list: Cummins/Onan 605MCCK →, Cummins/Onan MCCK →

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.

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