Cummins/Onan 5MDKAU — Replacing the Thermostat
Repair & overhaul
For the Cummins/Onan 5MDKAU, from the Cummins/Onan service manual.
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Before you start
- Hot coolant is under pressure; let the engine cool before loosening the pressure cap
Procedure
- Disconnect negative battery cable, let engine cool, remove top access door and pressure cap.
- Pack a towel around the thermostat housing flange to catch spilled coolant.
- Remove the two thermostat housing bolts and pull off housing, thermostat and gasket.
- Clean the gasket area and install the new thermostat and gasket.
- Apply Three Bond 1215 liquid sealant or equivalent to the top side of the gasket.
- Replenish lost coolant, secure pressure cap and access door, reconnect battery cables.
Specs & values
- Three Bond 1215 liquid sealant
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.