A reader asks: I’ve got a 2019 Ram 2500 with the 6.7L Cummins diesel. My manual says to use 10W-30 motor oil meeting the MS-10902 or API CJ-4 specification. I’m used to running a 5W-40 or 15W-40 in my previous trucks. Isn’t 10W-30 a bit thin for this engine?
Our answer: We can assure you that a good 10W-30 diesel motor oil is safe for your engine. But let’s discuss an important detail to watch for on the oil bottle label. This detail will improve the odds that your engine will receive the best possible wear protection.
When buying diesel motor oil, look for the “API CK-4” designation. API CK-4 is the very latest diesel engine oil standard. It is backward-compatible with API CJ-4 and Chrysler MS-10902 (and therefore warranty-approved).
Is API CK-4 An Upgrade Over API CJ-4 Diesel Oils?
Yes. The API CK-4 standard has very lofty requirements in terms of oxidation resistance, shear stability and wear resistance. It is dramatically superior to API CI-4+ motor oils you may have used 15 years ago. It is even a significant step up from the previous API CJ-4 standard. One of the primary goals of the API CK-4 spec was to allow for the use of lower viscosity oils without sacrificing wear protection.
Why Did Chrysler Decide To Go With 10W-30 In The 6.7L Cummins?
The move toward thinner oils in engines, transmissions and differentials has been going on for years. The reason is simple. Automakers are under constant pressure to meet government-mandated fuel economy targets. Going to lower viscosity oils is a relatively simple way to make marginal mileage gains.
It may seem like wear control is being sacrificed to achieve slightly better fuel economy. This has not turned out to be the case. The motor oil industry is constantly raising the bar to strike that balance between improved fuel economy and satisfactory wear protection. The API CK-4 specification achieves this balance.
Is 5W-40 An Option In Newer 6.7L Cummins Engines?
All this being said, Chrysler does suggest that 5W-40 engine oil can be used in temperatures under 0°F (-18°C). So 5W-40 is certainly secondary option. If your engine is seriously modified or if the truck is used for extreme towing, 5W-40 is certainly viable. But again, under most conditions, 10W-30 diesel oil is perfectly safe.
Our Motor Oil Suggestions For RAM 6.7L Cummins Diesel Engines
We suggest AMSOIL synthetic diesel oils (of course). Some brands may meet the API CK-4 standard. AMSOIL CK-4 diesel products are designed to exceed this spec. Here are the options.
Signature Series Max-Duty Synthetic Diesel Oil is AMSOIL’s ultra-premium API CK-4 diesel motor oil line. It is available in both 10W-30 and 5W-40 for the Cummins 6.7. It is also available in 15W-40, 5W30 and 0W-40. This series is designed to out-perform on every front. The most important is wear control. Signature Series exceeds the Detroit Diesel Scuffing Test standard by 600%. It is also overbuilt for extended-drain capability.
Heavy-Duty Series Synthetic Diesel Oil is AMSOIL’s commercial-grade API-CK-4 diesel line. This line is also available in 10W-30 and 5W-40 for the Cummins 6.7L motor. It is also available in 15W-40. Heavy-Duty Series has a lower price tag for commercial fleets and cost-conscious consumers. But it still delivers top-notch wear protection. It beats the Detroit Diesel Scuffing Test standard by 400%.
In conclusion, check the bottle for the API CK-4 specification. You will receive the very latest diesel oil technology.
If you are interested in pricing for highly-effective AMSOIL Synthetic Diesel Engine Oils, contact us using the form on this page.
Cummins 6.7L diesel engine. AMSOIL used to offer the BMK25 dual remote system for Ram/Cummins engines, but this kit was discontinued back in 2012.