Peterbilt 357/378 Fuel Tank Caps

Frequently Asked Questions About Peterbilt 357/378 Fuel Tank Caps

Will this fuel tank cap fit my Peterbilt 357 or 378 without modification?

Fuel tank caps in this category are designed to match the thread size and neck diameter used on Peterbilt 357 and 378 fuel tanks. Because tank necks can vary slightly depending on the tank manufacturer and model year, we recommend checking the thread diameter and cap style of your current cap before ordering to confirm a proper fit.

What materials and finishes are available for these caps?

These caps are commonly offered in chrome-plated steel or polished aluminum, giving you a durable finish that resists corrosion from road salt, fuel exposure, and everyday weather. Chrome options tend to offer a brighter, mirror-like look, while aluminum caps are lighter and still hold up well over time.

Are these caps vented or non-vented, and does it matter?

Yes, fuel tank caps come in both vented and non-vented designs, and using the correct type matters. Vented caps allow air to enter the tank as fuel is drawn out, preventing a vacuum lock that can restrict fuel flow to the engine. Check whether your original cap is vented or non-vented and match that specification when ordering a replacement.

How do I know if it is time to replace my fuel tank cap?

Common signs include a cracked or worn gasket, a cap that no longer locks securely, fuel odor around the tank, or visible rust and pitting on the cap itself. A loose or damaged cap can allow moisture and debris into the tank or let fuel vapor escape, so it is worth replacing at the first sign of wear.

Do these caps include a locking feature to prevent fuel theft?

Some fuel tank caps in this category include a locking mechanism with a key, while others are non-locking and simply thread or latch into place. If fuel security is a concern for your truck, look for the locking option and be sure to check that the lock cylinder and key style match what you need before purchasing.