Cummins/Onan — Checking Inlet Air Restriction
Testing & diagnosis · Air intake piping
From a Cummins/Onan service manual covering: ST-50, T-18A, VT-50. Check it applies to your exact model before use.
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Procedure
- Attach vacuum gauge or water manometer in air intake piping at right angle to flow, one pipe diameter upstream.
- Operate engine until normal operating temperature is reached.
- Operate at rated speed and full load and take the reading.
- If restriction exceeds 25 inches [635 mm] of water, clean or replace dry type cleaner element.
- Replace damaged air piping, rain shield or housing.
- Remove extra bends or other sources of restriction.
Tools required
- vacuum gauge or water manometer Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Inlet air restriction maximum 25 inches [635 mm] of water
- At air cleaner maximum 20 inches [508 mm] of water
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.