Gates 31778D Fuel Tank Cap

Diesel Fuel Cap Security and Fitment

The Gates 31778D Diesel Only Locking Fuel Cap is a green, lockable fuel tank cap built for diesel engine applications that use a Quick-On cam style and pressure-vacuum venting. It is a direct-fit option for a wide range of Chevrolet, GMC, Ford, Dodge, Jeep, Toyota, and other diesel vehicles, including many GMC Savana, Chevrolet Express, and Ford Super Duty applications.

Gates’ heavy-duty fuel cap line is built for industrial and diesel service, with durable construction and application-specific fitment. The 31778D is a diesel-only locking fuel cap that helps maintain a secure seal while matching the required threaded filler neck and venting setup on listed vehicles.

• Diesel only locking fuel cap for diesel fuel tank applications
• Lockable design for added fuel security
• Green cap color for diesel identification
• Pressure-vacuum venting for listed applications
• Quick-On cam type for proper fitment on supported filler necks
• Cross-reference: Stant 10591D

Detailed Product Overview

Part number 31778D is engineered as a diesel-only locking fuel cap with a 1.77 thread diameter, 2.61 depth, and 2.91 shell diameter. The pressure-vacuum venting design supports the fuel system requirements of many older and newer diesel trucks, vans, and utility vehicles. If you are replacing a worn, missing, or non-locking cap on a Chevrolet Silverado 2500 HD, GMC Sierra 3500 HD, or Ford F-350 Super Duty, this Gates fuel cap provides the correct style for the listed applications.

Compatible With applications include Fits 2006-2013 GMC Savana 2500, N/A; Fits 2006-2013 GMC Savana 3500, N/A; Fits 2006-2012 Chevrolet Express 2500, N/A; Fits 2006-2012 Chevrolet Express 3500, N/A; and Fits 1999-2005 Ford F-250 Super Duty, N/A. The 31778D also appears across many Chevrolet Silverado, GMC Sierra, and Ford E-Series diesel configurations, making it a practical replacement when the original cap is damaged or no longer seals correctly.

What This Fuel Cap Helps Solve

• Missing or damaged diesel fuel cap
• Fuel tank opening that no longer locks securely
• Incorrect cap style on threaded filler neck applications
• Fuel odor or sealing issues caused by a worn cap seal
• Diesel identification needs for mixed-fleet service vehicles

Installation Notes and Tips

Verify the filler neck style before ordering, especially on Ford applications that specify a threaded filler neck. Confirm the vehicle uses a diesel-only locking fuel cap with pressure-vacuum venting and compare the cap dimensions to the original part. For best results, match the application notes exactly, since some listings require specific filler neck or chassis configurations.

Part number 31778D is listed for a broad range of diesel trucks and vans, including Chevrolet Express, GMC Savana, and Ford Super Duty models. Review the vehicle notes carefully before installation to ensure the cap style, venting, and locking design match the original equipment requirement.

Quality Assurance

Gates manufactures heavy-duty fuel caps for industrial and diesel engine applications, with a focus on durable construction and application-specific fitment. This product line is intended to serve demanding diesel service environments while maintaining the correct locking and venting characteristics for the listed vehicles.