Frequently Asked Questions About Peterbilt 379 Fuel Tank Caps

Will these fuel tank caps fit my specific year Peterbilt 379?

Most aftermarket fuel tank caps for Peterbilt 379 trucks are designed to fit models from 1987 to 2007. However, there can be variations based on your specific tank configuration. Standard caps typically fit 4-inch tank openings, which is the most common size for 379 models. We recommend measuring your current cap diameter or checking your tank specifications before ordering. If you have dual tanks, ensure you order the correct quantity and verify both tanks use the same size caps.

What's the difference between locking and non-locking fuel caps?

Locking fuel caps feature a built-in lock mechanism that requires a key to open, providing security against fuel theft and tampering. Non-locking caps use a standard twist-on design for quick access. Locking caps typically add about $15-30 to the cost but offer peace of mind, especially for drivers who park in unsecured areas. Both types should meet the same sealing standards, so security is the primary differentiator. Consider your parking locations and routes when deciding which option best suits your needs.

Are vented or non-vented caps better for my Peterbilt 379?

Vented caps are required for most Peterbilt 379 fuel systems to prevent vacuum buildup in the tank and ensure proper fuel flow. Using a non-vented cap when your system requires venting can cause engine performance issues, difficulty filling the tank, or fuel pump problems. Check your original cap or owner's manual to confirm whether you need vented caps. As a general rule, if your truck was originally equipped with vented caps, you must replace them with vented caps to maintain proper system operation.

How difficult is it to install a new fuel cap, and what should I check?

Installing a fuel tank cap is typically a simple twist-on process that takes less than a minute. Before installation, inspect the tank neck threads for damage or corrosion and clean any debris. Check that the new cap's gasket or O-ring is properly seated and in good condition. Thread the cap on slowly to avoid cross-threading, and tighten until you feel resistance or hear clicks if it's a ratcheting design. After installation, check for fuel odors during your next few fill-ups to ensure proper sealing.

What materials and finishes are available, and which last longest?

Fuel tank caps come in several materials: aluminum (lightweight, corrosion-resistant), stainless steel (extremely durable, premium appearance), chrome-plated steel (attractive but may corrode if plating chips), and heavy-duty plastic (economical, functional). Stainless steel typically offers the longest service life, especially in harsh weather conditions. Aluminum provides excellent durability at a moderate price point. Chrome looks great initially but requires more maintenance. Consider your climate, budget, and aesthetic preferences when choosing. All materials should meet DOT requirements for proper sealing and safety.