ABOUT THE INTERNATIONAL A26

The International A26 is Navistar’s in-house inline-six heavy-duty diesel engine, introduced in 2016 for International LT and LoneStar trucks. It replaced the Maxxforce engine family following widespread reliability problems. The A26 displaces 12.4 liters and produces up to 500 hp and 1,750 lb-ft of torque.

Unlike Cummins or Detroit, International does not overlay a proprietary oil specification on top of the API category. If an oil meets API CK-4, it meets the A26 requirement. This mirrors PACCAR’s approach with the MX-13.

OIL SPECIFICATION

API CK-4 — NO PROPRIETARY SPEC

The A26 calls for API CK-4 directly. International does not maintain a separate approved product list or engineering standard beyond the API classification. Any genuine CK-4 oil from a reputable manufacturer qualifies.

FA-4: NOT APPROVED

FA-4 is a low-HTHS API category introduced alongside CK-4 in 2016. International has not published FA-4 approval for the A26. Run CK-4. Do not substitute FA-4 unless International explicitly approves it for your application and model year.

VISCOSITY GRADES

• 15W-40 — Primary grade for most operating conditions
• 5W-40 — Recommended for cold climates below −10℃ (14℉)
• 10W-30 — Check OEM manual for specific cold-weather guidance

DRAIN INTERVALS

• Standard: 15,000–25,000 miles for highway operation
• Extended: Oil analysis required for intervals beyond 25,000 miles
• Severe service (short haul, construction, high idle): reduce intervals accordingly

Always follow the maintenance schedule in your International service manual. Oil quality, fuel sulfur content, and duty cycle all affect optimal drain intervals.