newer Cummins 6.7L ... 5w40 vs 15w40

[Hohn]

Since I work in a different division of the big red C, I can't tell you what's going on with the 6.7L. I don't know if they went hydraulic across the board, or only for the FCA application because FCA forced them to.

I can tell you that if you tried to get engineering approval for hydraulic tappets in my world (larger industrial engines 19L and up), you'd probably get laughed out, and "mentored" by a more senior engineer.

In theory, I might be able to find some internal test reports on the 6.7 hydraulic lifter... Cannot disclose obviously, but would be interesting.

 

[johnmyster]

It's just too hard to put in customer language something like "Oil must be API Group III or higher base."

But what they could do is (be like Ford and) make up a new specification Cummins CES 20087.FCA.1, which specifies what they need for the goals in mind and back spec it for all 6.7s, ever. From there the specification says whatever it needs to say. Viscosity, HTHS, cleaning tests, oxidation tests, etc. Then, issue a 2019+ recall for hydraulic lifter models where the only action is to put a sticker on the oil cap with the new spec. Boom, done.

Ram truck bro diesel independent thinker mall crawl types hate dealer-only conspiracy fluids. Rotelladelovac Blue would scramble to get compliant lubricants on the shelf at wally world. Buy five gallons get a free belt buckle promotion. Docs diesel and Hot Shot Secret would come out with a rebottled $30/gal version. Amsoil, Redline, Schafer, and CenPeCo would claim compatibility, "recommended for."

 

[OLEJOE]

But what they could do is (be like Ford and) make up a new specification Cummins CES 20087.FCA.1, which specifies what they need for the goals in mind and back spec it for all 6.7s, ever. From there the specification says whatever it needs to say. Viscosity, HTHS, cleaning tests, oxidation tests, etc. Then, issue a 2019+ recall for hydraulic lifter models where the only action is to put a sticker on the oil cap with the new spec. Boom, done.

Ram truck bro diesel independent thinker mall crawl types hate dealer-only conspiracy fluids. Rotelladelovac Blue would scramble to get compliant lubricants on the shelf at wally world. Buy five gallons get a free belt buckle promotion. Docs diesel and Hot Shot Secret would come out with a rebottled $30/gal version. Amsoil, Redline, Schafer, and CenPeCo would claim compatibility, "recommended for."

You left out common sense people who are trying to make a living with these trucks while you were stereotyping people who own or drive diesel pickups.

 

[OLEJOE]

Since I work in a different division of the big red C, I can't tell you what's going on with the 6.7L. I don't know if they went hydraulic across the board, or only for the FCA application because FCA forced them to.

I can tell you that if you tried to get engineering approval for hydraulic tappets in my world (larger industrial engines 19L and up), you'd probably get laughed out, and "mentored" by a more senior engineer.

In theory, I might be able to find some internal test reports on the 6.7 hydraulic lifter... Cannot disclose obviously, but would be interesting.

The hydraulic roller lifters are only in the engines in the Ram trucks. The Cummins 6.7s that are used in other commercial vehicles and industrial engines are still the flat tappet engines.

 

[Hohn]

The hydraulic roller lifters are only in the engines in the Ram trucks. The Cummins 6.7s that are used in other commercial vehicles and industrial engines are still the flat tappet engines.

Which suggests to me that Stellantis or whomever owns Ram now (I haven’t checked in months) likely dictated the use of hydraulic lifters.

It recalls to me how Ford micromanaged aspects of the Navistar design and the resulting issues on the Powerstrokes (curiously not seen on navistar’s own engines), ultimately ended the business relationship, at least that was the rumor I heard.. I don’t think anyone disputes that the 6.0 and 6.4 weren’t home runs of reliability.

 

[userfriendly]

I do not honestly know? Just an opinion on my part not a fact, I'm guessing the 10w30 or 5w40 is required on the 2019's and newer due to tolerances with new designs. If I had a 2019 or newer, I would not use the 15w40. I would follow the Cummins Guidelines.

I heard that it’s because of the hydraulic lifters and black soot filled oil are a bad combination on 2019-2024 models.
The 10w30 and 5w40 only options instead of 15w40 with its thicker base oil viscosity buys enough time to get the engine out of warranty.
Sources say that the 2025 models have gone back to mechanical lifters.
People complain about the typewriter sound Duramax engines make.
I’d rather listen to a little valve train clatter than be broken down on the side of the road.

 

[6.7 CTD]

2025 6.7 is still using the hydraulic roller lifters; however, they did change suppliers for the rollers.

 

[OLEJOE]

Hamilton Cams has a solid lifter kit with the cam, lifters, adjustable rocker arms and custom push rods to eliminate the roller lifters. That’s the route Im going if mine goes out. Expensive, yes but cheaper than trading for another ticking time bomb.

 

[johnmyster]

People complain about the typewriter sound Duramax engines make.
I’d rather listen to a little valve train clatter than be broken down on the side of the road.

The older Duramax (LML and prior) wouldn't have been as ticky if there had been a valve adjustment interval ascribed to them. It was just a part of their character.

Isn't the 6.7 powerstroke a hydraulic roller lifter (and a fairly complex dual pushrod unit at that.) Didn't the duramax L5p go to hydraulic? Why don't we see lifter/cam failure as a characteristic of those motors?

 

[userfriendly]

Maybe they drilled out the oil galleries.

 

[NiwradND]

Im thinking 0w40 rotella will help with the roller problems on the cummins.

 

[OLEJOE]

I think it’s more a difference if the lifters are made from recycled sardine cans or recycled plow shears is why some fail and some don’t. I don’t think hydraulic lifters are a good idea with the amount of soot the current engines are having to digest because of EGR. The particle size may not cause wear but in sufficient quantities probably disrupts the flow through the lifters.
I know I have had problems with flat hydraulic lifters in gasoline engines on new engines. It only takes one piece of something that can’t pass through the orifice in the lifter to convert it into a solid lifter and start hammering.

 

[BrianF]

I suspect not only an engineering issue but parts supplier as well. Look at the 6.7 water pump recall. One supplier was fine and the other were junk. Look at all the cam and lifter issues with the gas engines. Penny pinching and a race to the bottom.

 

[NiwradND]

i just read the 2025 manual and it now says ony 5w40 or 0w40. I still thinking 0w40 will do a better job on the 19-24 models. Im going to try some Rotella 0w40 year around in my 21. I think that will help with oil flow through the lifters.

 

[6.7 CTD]

So you’re assuming it is only the cold flow that is contributing to the failure? If anything, I’d want a 5w40 over 0w40 as there are likely less VI in the 5w40; especially if the concern is deposits.

 

[kschachn]

So you’re assuming it is only the cold flow that is contributing to the failure? If anything, I’d want a 5w40 over 0w40 as there are likely less VI in the 5w40; especially if the concern is deposits.

And not only that, “cold flow” is highly dependent on the temperature and the specific oil. There is no guarantee that any particular oil with a 0W winter rating is thinner than one with a 5W rating except at temperatures below about -30. Above that it can very well be thicker.

This is not and cannot be about “cold flow”. It is about deposit formation from what they consider to be inferior 15W-40 oils and they are trying to mitigate that by backhandedly mandating the use of a better base stock oil through a winter rating. “Flow” is not the issue.

 

[userfriendly]

Instead of throwing darts at a board, 20 years ago the discussion would turn to viscosity and shear stress and post a scientific study of the base oil viscosity of 0w40 vs 15w40 flowing through an oil gallery.
Understanding fluid dynamics 101.

 

[johnmyster]

Instead of throwing darts at a board, 20 years ago the discussion would turn to viscosity and shear stress and post a scientific study of the base oil viscosity of 0w40 vs 15w40 flowing through an oil gallery.
Understanding fluid dynamics 101.

Except that the failures are not limited to the coldest climates. If viscosity is non linear, we'd expect to see many more failures amongst trucks that see a greater magnitude and frequency of cold operation. Dealers north of the 45th parallel would be swapping motors at 10x the rate of those south of the 35th...for instance.

The correlation/causation seems to be far looser.

My casual observation on the cummins forums/groups is that 90% of the armchair experts don't actually know how a hydraulic lifter works. It's not like a bearing where you need sufficient flow to maintain lubricating film appropriate to RPM. On top of this they confuse roller vs flat-tappet with hydraulic vs solid. You could have deposits killing the hydraulic aspects while lubrication/design/materials issues could be wiping roller cams.

 

[kschachn]

Except that the failures are not limited to the coldest climates. If viscosity is non linear, we'd expect to see many more failures amongst trucks that see a greater magnitude and frequency of cold operation. Dealers north of the 45th parallel would be swapping motors at 10x the rate of those south of the 35th.

The correlation/causation seems to be far looser.

My casual observation on the cummins forums/groups is that 90% of the armchair experts don't actually know how a hydraulic lifter works. It's not like a bearing where you need sufficient flow to maintain lubricating film appropriate to RPM.

IIRC they even state that deposits are the issue.

 

[johnmyster]

IIRC they even state that deposits are the issue.

Correct, which is frequently ignored. I think there are two issues at play.

1) The 2019+ hydraulic lifters are susceptible to DEPOSITS in a way old solids were not. 15k OCI and EGR soot exacerbates this.
2) The 2019+ roller lifters are susceptible to cam chewing the cams due to bad materials and the reduced contact area of roller vs flat tappet. 15k OCI fuel dilution (largely occurring during regen due to post injection) exacerbates this.

Both of these can be helped but not entirely corrected by better oil. One is a cleaning issue and the other is a design/lubrication/wear issue. The first is why the engines get noisy and make owners nervous. The second is why they fail. The TSB acknowledges one but not the other.

IIRC, the 2025 ram gets an indirect DEF doser injector, like the L5P and the later 6.7 powerstrokes. This would help impacts of fuel dilution. I'm pretty sure Cummins ISX has one...@Hohn can shed more light on this.