2018 Chevrolet Silverado 3500HD Transmission Fluid & Service Spec

Quick Answer

• Transmission Make/Model: Allison 1000 Series (6-speed automatic)
• OEM Fluid Spec: Dexron VI (not TES 295/668 for this particular Allison, as it's a lighter-duty version for non-commercial applications)
• Drain & Fill Capacity: Approximately 7.4 quarts (7.0 liters)
• Full Overhaul Capacity: Approximately 12.7 quarts (12.0 liters)
• Filter OEM Part Number: Verify with dealer or service manual (often AC Delco 24236933 for internal filter, check for pan gasket separately)
• Recommended Service Interval: Normal Duty: 97,500 miles (150,000 km) or 72 months, whichever comes first. Severe Duty/Towing: 45,000 miles (72,000 km) or 48 months, whichever comes first.

Fluid Type Explained

The 2018 Chevrolet Silverado 3500HD, when equipped with the Duramax 6.6L diesel engine, typically utilizes the robust Allison 1000 Series six-speed automatic transmission. Unlike some heavier-duty commercial Allison transmissions that require TES 295 or TES 668 fluids, the Allison 1000 in consumer-grade pickups is designed to operate with Dexron VI fluid.

Dexron VI is a full synthetic automatic transmission fluid developed by General Motors. It offers improved friction durability, enhanced wear protection, and better resistance to oxidation and shear stability compared to older Dexron specifications. Using any other fluid type can lead to premature wear, poor shift quality, and potential transmission failure. Always ensure that any aftermarket fluid explicitly states compliance with or meets the Dexron VI specification.

Service Procedure

There are two primary methods for servicing your transmission fluid: a simple drain and fill or a full fluid exchange (often called a "flush").

Drain and Fill: This method involves removing the transmission pan, allowing the fluid to drain out, replacing the filter, and then refilling the transmission with new fluid. For the Allison 1000 in your 2018 Silverado 3500HD, a drain and fill will typically replace about 7.4 quarts (7.0 liters) of fluid. This method is effective for regular maintenance as it removes a good portion of the old fluid and contaminants. However, it does not remove all of the old fluid, as a significant amount remains in the torque converter and cooler lines.

Full Fluid Exchange (Flush): A full fluid exchange involves using specialized equipment to pump new fluid through the transmission, pushing out all of the old fluid. This process replaces nearly 100% of the transmission fluid, including what