Cummins/Onan QST30 — Coolant Thermostat Replacement
Repair & overhaul
For the Cummins/Onan QST30, from the Cummins/Onan owner's manual.
Applies to: Cummins/Onan G-Drive, Cummins/Onan QST30, Cummins/Onan QST30 engine
Before you start
- Tilt the housing to prevent the thermostats from falling out.
Procedure
- Drain the cooling system.
- Remove the thermostat housing.
- Remove the thermostats and seals.
- Clean all gasket surfaces and bores.
- Inspect thermostat; discard if barrel is worn or fretted.
- Install the thermostat by pushing on the outer rim.
- Install seals with the seal lip positioned up.
- Fill the cooling system and check for leaks at 70 C [160 F].
Tools required
- Thermostat seal driver ST1225 Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Seal no more than 0.57 mm [0.020 in] below the top of the cast edge
Full service-parts list: Cummins/Onan QST30 →
Source: Cummins/Onan owner'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.