The typical socket size to loosen the fuel filter housing cap on a 2018 Ram 3500 with the 6.7L Cummins is 24 mm. You can use a standard 24 mm socket or the dedicated Mopar fuel filter cap wrench that fits the housing.
In practical terms, the Ram 3500’s fuel filter setup includes a primary water-separator filter housed in a round cap at the engine bay, with some configurations also using a secondary filter. The cap is designed to be removed with a socket or a specialized cap wrench. Always start with the engine off and relieve fuel pressure before attempting any change, and follow the manufacturer’s instructions for filter replacement and resealing.
Understanding the fuel filter setup
The 2018 Ram 3500’s diesel engine (Cummins 6.7L) uses a replaceable primary fuel filter, and some configurations include a secondary filter. Accessing the filter involves removing the round cap on the fuel filter housing, which is sized to accept a 24 mm socket or an equivalent cap wrench. Variations by build date or aftermarket modifications may alter the exact tool fit, so verify the cap flats if you have any doubt.
Notes on model-year variants
Some trucks can differ slightly in their filter housing design due to production changes or aftermarket upgrades. If a 24 mm socket doesn’t seat properly, measure the flats on the cap with a caliper or refer to Mopar’s service tooling guide for the exact cap wrench size for your specific vehicle configuration.
Below are the practical steps and tools commonly used to perform a fuel filter change on the 2018 Ram 3500 with the 6.7L Cummins.
Below is a step-by-step guide to replacing the primary fuel filter, including how the 24 mm socket fits into the process.
- Relieve fuel pressure by turning the ignition to ON and OFF a few times with the engine off, then set the parking brake and wear gloves.
- Locate the fuel filter housing in the engine bay, typically on the driver's side near the firewall; identify the round cap.
- Using a 24 mm socket (or the dedicated cap wrench), loosen the cap counterclockwise until it can be turned by hand.
- Remove the cap and lift out the old filter; inspect and replace the O-ring on the cap if present; prepare the new filter per the kit instructions.
- Lubricate the new O-ring with clean diesel fuel or oil as recommended, insert the new filter, and reseat the cap.
- Close and hand-tighten the cap, then snug with a wrench until seated; do not over-tighten.
- Start the engine and check for leaks; allow the fuel system to prime and bleed any air; inspect for drips at the cap.
The steps above cover the basic procedure for the primary filter in most configurations. If your Ram uses a secondary filter or a different sequence, refer to the service manual for specifics.
Tools and safety equipment you’ll typically need for this job:
- 24 mm socket or the Mopar cap wrench specifically designed for the fuel filter housing
- Ratchet or breaker bar for extra leverage if the cap is tight
- Fuel-safe catch pan to collect any spilled diesel
- Rags, gloves, and eye protection
- Optional torque wrench if you want to apply a specific seating torque (consult the manual)
Having the right tool in hand helps prevent damage to the housing and ensures a proper seal. If the 24 mm size doesn’t fit, verify with the dealer or a shop manual rather than forcing a fit, which could deform the cap.
Safety considerations and maintenance tips
Safety first: work in a well-ventilated area, keep ignition off, and have a spill containment plan. Diesel fuel is a skin irritant and flammable. Dispose of used filters according to local regulations, and wipe up any spills promptly. If you encounter a cap that won’t budge with a proper tool, avoid using excessive force and consult a professional.
Summary
For a 2018 Ram 3500 with the 6.7L Cummins, you’ll generally use a 24 mm socket or a dedicated cap wrench to remove the fuel filter housing cap. Follow the step-by-step procedure, ensure a clean seal with a new filter and O-ring, and check for leaks after starting the engine. If you notice any variation in your build, refer to the dealer’s service documentation for the exact tool size and torque guidance.