Diesel engines are common in Oklahoma — whether you’re driving a Ram 2500 with a Cummins, a Ford F-350 with a Power Stroke, or a Silverado 2500 with a Duramax, these engines have fundamentally different oil requirements from gasoline engines. Using the wrong oil — or the wrong change interval — can cause real damage. Here’s what you need to know.
Why Diesel Oil Is Different
- Higher soot loading — Diesel combustion produces significantly more soot than gasoline combustion; diesel oil contains more robust dispersants and detergents to handle this soot load
- Higher alkalinity (TBN) — Total Base Number measures oil’s ability to neutralize sulfuric acid from combustion; diesel oil has higher TBN to manage diesel fuel combustion byproducts
- Different additive package — Diesel oil contains different anti-wear and anti-oxidation additives appropriate for diesel engine wear patterns and temperatures
- API CK-4 (current standard): The current API diesel oil standard for 2017+ diesel engines; backward compatible with older CJ-4 applications
Diesel Oil Change Intervals
- Ram 2500/3500 with Cummins 6.7L: 7,500 miles or 6 months with diesel oil; reduce to 5,000 miles with heavy towing
- Ford F-250/350/450 with Power Stroke 7.3 or 6.7L: 7,500 miles or 12 months with Motorcraft 15W-40 or 5W-40 synthetic; 5,000 miles under towing
- Chevy/GMC 2500/3500 with Duramax L5P or LML: 7,500 miles with dexos-D spec oil; reduce significantly under towing conditions or with DEF-system issues
Never Use Gasoline Engine Oil in a Diesel
Using API SP (gasoline-rated) motor oil in a diesel engine won’t cause immediate visible problems but will result in insufficient soot management, leading to faster oil degradation and eventual accelerated wear on rings and bearings. Always use API CK-4 or FA-4 rated oil in diesel applications.
Norm’s Auto Clinic services diesel pickup trucks with correct diesel-specification oils. Call (918) 279-8100 or visit 19 N. Broadway, Coweta, OK 74429.