The 2018 Ram 2500 offers drivers the option of a robust Cummins 6.7L diesel, a performance-oriented gasoline V8, or a capable gasoline V6. Selecting the correct oil type is essential for protecting the powertrain, meeting emissions standards, and preserving resale value across these configurations.
This article breaks down the recommended viscosities, specifications, and best practices for the 2018 Ram 2500, with a special focus on the demands of the Cummins diesel and how conventional, synthetic, and blended formulations perform in demanding conditions.
| Engine Option | Factory Fill (Quarts) | Recommended Oil Type | Filter Part Number |
|---|---|---|---|
| Cummins 6.7L I6 Turbo Diesel | 12 | CJ-4 or CK-4, API-rated, synthetic blend or full synthetic | Original Mopar 68043969AB |
| 6.4L HEMI V8 (Diesel Competition) | 12 | SJ, SL, or SM viscosity gasoline motor oil | Mopar or equivalent high-flow filter |
| 5.7L HEMI V8 | 6.4 | SJ, SL, or SM gasoline motor oil, 5W-30 or 5W-40 | Mopar PF6729303AA or standard canister |
| 6.7L Power Stroke (6BT) Diesel | 15 | CF-4 or CI-4, 15W-40 preferred for towing | Fleetguard LF670 or equivalent spin-on |
Understanding Cummins Requirements in the 2018 Ram 2500
The heart of many 2500s is the Cummins B-series diesel, a unit that balances efficiency with formidable low-end torque. Because it operates at higher pressures and temperatures than typical gasoline engines, its oil faces unique thermal and soot loading challenges.
For the 2018 model year, factory specifications almost always call for CJ-4 or the later CK-4 rating, along with an ACEA E rating when available. These designations ensure the oil can manage the byproducts of modern aftertreatment systems while protecting the rocker assemblies and turbochargers.
If you plan to tow heavy trailers day after day, many owners and dealers recommend upgrading to a CK-4 or even a full synthetic CJ-4 formulation. The extra thermal stability and shear protection help extend drain intervals, especially in stop-and-go traffic or hot climates where the radiator sees constant use.
Conventional, Synthetic Blend, and Full Synthetic Options
Conventional mineral oils remain a budget-friendly choice for light-duty use, but they break down faster under the cyclic high-load conditions that diesel owners often encounter. If your 2500 mostly sits in the driveway or pulls a tiny trailer, conventional CJ-4 oil with a 15W-40 viscosity can suffice, albeit with more frequent changes.
Synthetic blends strike a middle ground, combining affordable base stocks with synthetic additives that improve cold-start flow and thermal retention. For the 2018 Ram 2500 equipped with the Cummins engine, a high-quality synthetic blend can offer better protection during mountain passes, extended idling at job sites, and improved fuel economy during highway hauls.
Gasoline Engine Oil Strategies for the 6.4 and 5.7 HEMI
Owners who opt for the 6.4L HEMI or the smaller 5.7L HEMI in the 2018 Ram 2500 still need to respect manufacturer guidance, even if diesel-specific concerns do not apply. The 6.4L benefits from oil formulations that address its higher compression and forced-induction tendencies, while the 5.7L has its own nuances tied to variable valve timing and MDS operation.
For gasoline variants, meeting API SJ, SL, or SM service standards is typically sufficient when using the recommended 5W-30 or 5W-40 rating. In particularly hot climates or for trucks that consistently tow at high altitudes, some drivers choose a 10W-30 or 10W-40 to help maintain film strength and oil pressure during long uphill grades.
Best Practices for Oil Changes and Filter Selection
Routine maintenance on the 2018 Ram 2500 extends beyond simply swapping oil. Using the right filter, torque specs, and disposal methods ensures that every change delivers maximum protection and compliance with warranty expectations.
When the drain plug is removed, allow the oil to cool slightly so that suspended contaminants can settle, but not so long that sludge adheres stubbornly to the pan walls. Pair each oil change with a new OEM-style or premium aftermarket filter, and apply a light film of fresh oil to the gasket before seating the filter by hand to prevent cross-threading and premature leaks.
Key Recommendations for Longevity and Performance
- Always choose CJ-4 or CK-4 for the Cummins diesel and SJ/SL or SM for the gasoline V8 and V6 options.
- Match the viscosity to your climate: 15W-40 for most diesel work, 5W-30 or 5W-40 for gasoline variants, adjusting for extreme temperatures.
- Use a high-efficiency spin-on filter with a silicone anti-drain back valve to minimize startup wear between changes.
- Follow the recommended change intervals for severe service when towing, idling, or operating in dusty environments.
- Verify API markings on the oil container and retain service records to support warranty and resale value.
FAQ
Reader questions
What viscosity and rating should I use in the 2018 Ram 2500 with the Cummins 6.7L diesel?
Use CJ-4 or CK-4 rated oil, 15W-40 for most conditions. In very cold climates, a 5W-40 synthetic may improve cold starts, while hotter regions or heavy towing may benefit from careful selection of a 15W-40 high-mileage or full synthetic formulation.
Can I use the same oil in the gasoline 6.4L and diesel Cummins engines?
Not directly, because the diesel requires CJ-4/CK-4 and an ACEA E rating, while the gasoline 6.4L needs gasoline-specific SJ/SL or SM oils. Always follow the label on each oil bottle and the specifications listed in your owner’s manual for each engine option.
Is it okay to switch between conventional and synthetic oil in my Ram 2500?
Yes, you can switch between conventional and synthetic without issues, provided the viscosity and API ratings match the vehicle requirements. The blend will not damage the engine, though you may not immediately realize the full performance benefits of a full synthetic.
How often should I change the oil if I frequently tow with the Cummins diesel?
For severe towing conditions, shorten the drain interval from the standard 10,000–15,000 miles to around 7,500–10,000 miles. Pair this with a high-quality CJ-4/CK-4 synthetic or synthetic blend and a top-tier filter to maintain turbocharger durability and aftertreatment system efficiency.