Best Oil for 6.7 Cummins: What to Use and Avoid

The oil aisle almost beat me

I stood in the oil aisle at Canadian Tire for twenty minutes one Saturday trying to find the best oil for 6.7 Cummins ownership, and I am not proud of that. My buddy swears by one brand. The dealer parts counter swears by another. The forums are at war over weights with letter codes that look like license plates. All I wanted was the right jug and I walked out more confused than when I walked in.

Short version: check your model year first, because that decides your viscosity. Then buy any jug that lists Cummins CES 20086 and API CK4 on the back. Brand barely matters. Ask me how I know.

Quick note on money, because I keep track: everything below is in Canadian dollars. The 6.7 takes 11.4 litres with the filter, which is 12 quarts, so a full change is a real pile of oil and the price matters.

6.7 Cummins oil type: read the back of the jug

Forget the front of the jug. The marketing words mean nothing. Turn the jug around and look for three things.

First, Cummins CES 20086. That is Cummins own engineering standard, and it lines up with API CK4. Older trucks that spec CES 20081 and CJ4 are fine with CK4 too, since it covers everything the older spec did. If the jug does not list a CES number at all, put it back on the shelf.

Second, API CK4 in the round donut. The C means diesel rated. Gas engine oil has an S rating and cannot handle the soot a diesel makes. Oil turning black fast is normal, but it has to be built to carry that soot without turning to sludge, and CK4 oil is.

Third, MS10902, which is the FCA material standard Ram puts in the diesel supplement. Most big diesel oils on the shelf carry it. If your manual says your truck wants it and the jug does not list it, keep looking.

I learned this the hard way. I once grabbed a jug with all the right words on the front and nothing on the back. No CES number, no CK4. Drove it right back to the store. Ten minutes of reading in the aisle beats draining the wrong oil in the driveway.

If you want the full picture on how this engine holds up when you treat it right, read 67 Cummins reliability.

15W40 vs 5W40 in the 6.7 Cummins: the model year split

The 2019 and newer 6.7 got a redesigned valve train with hydraulic valve lash adjusters. If you run 15W40 in one of those trucks, deposits form in the adjusters. The bulletin says it plain: noise, and possible engine damage. That is not a forum rumor. That is Ram telling its dealers.

So the rules, straight from the book:

2018 and older: 15W40 above 0 F, and 5W40 full synthetic when winter mornings drop below 0 F, which is minus 18 C.

2019 and newer: 10W30 above 0 F, and 5W40 full synthetic below 0 F. 15W40 is not allowed, period.

All years: the 5W40 synthetic is safe to run all year, even in summer heat. It just costs more.

That settles the 15W40 versus 5W40 argument. The answer is what year your truck is and how cold your mornings get.

Oils to keep away from this engine

The avoid list, plain and simple:

1. 15W40 in any 2019 or newer 6.7. Covered above. Do not do it.

2. Any oil without a diesel rating. If the donut only has an S category and no C category, it is gas engine oil. It is not built for soot and it will not protect your turbo bearings. The turbo on this engine spins on a film of oil thinner than a hair. Give it the wrong oil and you are gambling with the most expensive part under the hood.

3. Mystery oil with no CES number on the back. House brands can be fine if they are actually licensed, and the proof is on the back of the jug. No CES 20086 or 20081 listed means no proof. I do not put unproven oil in a truck that drinks 11.4 litres a change.

4. Anything not CK4 or CJ4 rated in a truck with its emissions gear still on it. The aftertreatment gear on these trucks is sensitive to ash and additives, and the wrong oil poisons it slowly. I mean oil that plays nice with the emissions system your truck came with. I am not telling you to touch the system itself.

Stick to names that carry the ratings: Rotella T6, Delvac, Valvoline Premium Blue, Petro Canada Duron. I am not sponsored. I buy whichever licensed jug is on sale.

Best oil for a 6.7 Cummins in an Alberta winter: what I run

My truck lives outside in Alberta, where minus 30 is a normal February morning. Here is my year:

October to April it gets 5W40 full synthetic. Rotella T6 is what I buy most because it goes on sale the most. The book requires 5W40 below minus 18 C anyway, and half my winter mornings are below that before I turn the key. Thin oil on a cold start is the cheapest insurance there is. I would run it all year if I only wanted one jug in the garage.

May to September, it gets 10W30 CK4. That is the book answer for a 2019 or newer truck in warm weather, and it is usually a few dollars cheaper per jug than the synthetic. If your truck is a 2018 or older, your summer answer is 15W40, same logic.

What it costs me, because I know you are wondering: the 18.9 litre pail of T6 lists at 259.99 at Canadian Tire right now, but I have never paid that. It goes on sale for 170 to 200 often enough that I buy ahead and keep a pail in the garage. At sale prices my 11.4 litres works out to roughly 100 to 130 dollars in oil, plus a Fleetguard LF16035 filter, which is the filter Cummins puts its own name behind. Mopar MO285 is the same idea from the dealer. I do the change in the driveway in about an hour. Call it 150 to 180 dollars all in when I buy smart.

If winter is what worries you, the winter diesel survival guide covers the rest of the cold weather routine.

Change intervals: what the book says versus what I do

The manual says this: follow the oil life indicator, or every 24,000 km, 12 months, or 500 engine hours, whichever comes first. The 500 hours part is the one that gets people, because idling counts. A truck idling all day on a job site can hit 500 hours with low kilometres on the clock.

I change it around 16,000 km in my driveway, sooner if the winter was full of idling and short trips. Oil is cheap. Engines are not. I once stretched a change because work was slammed and the oil came out looking like it had given up on life. Never again.

If you want to run the full book interval, get an oil analysis. A lab tells you exactly how your oil is holding up. Without a lab report you are guessing, and guessing with 11.4 litres in the engine that pulls your trailer is bad math.

While you are under there, it is worth knowing the filter side of the routine too: fuel filters OEM vs aftermarket.

My recommendation

Check your model year first. 2019 or newer means 10W30 in summer, 5W40 synthetic in winter, and never 15W40. 2018 or older means 15W40 in summer and 5W40 synthetic in winter. Buy a jug that lists CES 20086 and API CK4 on the back, pair it with a Fleetguard LF16035 or Mopar MO285 filter, and change it on time.

Do that, and the 6.7 will do what it is famous for: start every cold morning and pull whatever you hook to it. The oil is the cheapest part of owning this truck. Treat it that way.

Frequently asked questions

Can I run 15W40 in a 2019 or newer 6.7 Cummins?

No. Ram's July 2020 oil bulletin says 15W40 causes deposits in the hydraulic valve lash adjusters of the redesigned valve train, which leads to noise and possible engine damage. Use 10W30 above 0 F and 5W40 full synthetic below 0 F.

How much oil does a 6.7 Cummins take?

12 quarts, or 11.4 litres, with the filter changed. Fill it, run it, let it sit a minute, then check the dipstick. Do not overfill.

How often should I change the oil in my 6.7 Cummins?

Follow the oil life indicator, or every 24,000 km, 12 months, or 500 engine hours, whichever comes first. Heavy idling, towing, and cold short trips shorten that in real life.

What oil does the 6.7 Cummins take in winter?

5W40 full synthetic on every model year. Ram requires it whenever mornings routinely drop below 0 F, which is minus 18 C. It flows on a cold crank when thicker oil stays put, and the bulletin says it is safe to keep running it through summer.

What does Cummins CES 20086 mean?

It is Cummins own engineering standard for diesel engine oil, and it lines up with the API CK4 category. CES 20086 covers everything the older CES 20081 and CJ4 specs did. Look for it printed on the back of the jug as proof the oil is actually licensed for this engine.

Can I run 5W40 all year in my 6.7 Cummins?

Yes. Ram's oil bulletin says 5W40 full synthetic is safe in summer heat and warm climates on every model year. Many owners run one jug year round. It costs more than 15W40 or 10W30, but it is the simplest answer to the winter question.