Cummins/Onan — Testing Compression
Testing & diagnosis · Engine
From a Cummins/Onan service manual covering: P216, P218, P220, P248. Check it applies to your exact model before use.
Applies to: Cummins/Onan P216, Cummins/Onan P218, Cummins/Onan P220, Cummins/Onan P248
Before you start
- Hot engine components can cause severe personal injury if touched. Use extreme caution when working on a hot engine.
Procedure
- Run the engine until thoroughly warm.
- Stop the engine and remove the spark plugs.
- Remove the air cleaner and place the throttle and choke in the wide open position.
- Insert the compression gauge in one spark plug hole.
- Crank the engine and note the reading.
- Refer to Section 2 Specifications for compression pressures (about 300 rpm cranking speed).
Tools required
- compression gauge Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Cylinder compression 75 - 115 psi (517 - 793 kPa) for a warm engine at cranking speed (about 300 rpm)
Full service-parts list: Cummins/Onan P216 →, Cummins/Onan P218 →, Cummins/Onan P220 →, Cummins/Onan P248 →
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.