Cummins/Onan — Coolant Thermostat Function Test
Testing & diagnosis
From a Cummins/Onan owner's manual covering: 6CTA8.3, CFP83-F10, CFP83-F20, CFP83-F30, CFP83-F40. Check it applies to your exact model before use.
Applies to: Cummins/Onan 6CTA8.3, Cummins/Onan CFP83-F10, Cummins/Onan CFP83-F20, Cummins/Onan CFP83-F30, Cummins/Onan CFP83-F40, Cummins/Onan 6CTA8.3G2 engine, Cummins/Onan 6CTAA8.3G3 engine
Before you start
- Do not remove the pressure cap from a hot engine.
Procedure
- Start the engine and allow it to approach operating temperature.
- Monitor the operation of the thermostat; initial opening temperature MIN 81°C [178°F], MAX 83°C [181°F].
- Stop the engine when the coolant starts to flow.
- If the coolant does not start flowing in the initial opening range, the thermostat must be replaced.
- Install the heat exchanger hose and tighten the hose clamp.
Tools required
- Thermocouple or temperature gauge (optional) Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Thermostat initial opening MIN 81°C [178°F], MAX 83°C [181°F]
Full service-parts list: Cummins/Onan CFP83-F10 →, Cummins/Onan CFP83-F20 →, Cummins/Onan CFP83-F30 →, Cummins/Onan CFP83-F40 →
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.