2005 Isuzu Other NPR HD 5.2L Diesel

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For the air cleaner, it should be somewhere behind the front wheels, hidden by the mudflaps.
Belt adjustment are usually done by releasing a nut holding the adjuster pulley and making turns on the adjuster bolt (if equipped).
Since information is not available, I believe it should be somewhere around 10 quarts. Check with the parts store, they should be able to provide you with the infirmation.