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5w40 vs. 10w30 vs..... 5w30?

ErikTheRed

ErikTheRed

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So Ive been doing alot of reading lately on multi-weight oils for our trucks, and Ive come to the very non-professional and barely educated conclusion that probably the best option for a year-round oil weight for the 19+ 6.7 (at least in the valley of Commiefornia where 30 degrees is COLD) would be a 5w30. Because of the potential for lifter failure and it's close relationship to proper oiling, its critical that oil get to those components asap when the engine is first started, especially during the cold months. Thats the 5w part. But even after warm-up, and in the summer months, those components will still need good oil flow to stay lubricated, and I fear that a 40w might still be too "thick" for these modern engines and could be contributing to the lifter issues. So, even though Cummins didn't spec the weight as an option, a 5w30 would probably be the best of both worlds-- because the 10w30 is too thick at cold start-up and the 5w40 is still too thick at operating temps. This is my theory. Which leads me to a couple questions.... 1, would I be jeopardizing warranty using this oil weight? and 2, Shell does not make the Rotella T6 in a 5w30, but they do make it in a "MV" or Multi-Vehicle oil, which they describe as a good oil for heavy duty diesel use. What say you?
 
Also, I noticed that Mobile Delvac full syn diesel oil is available in a 5w30. I used Delvac 15w40 for years in my 06 5.9 and never an issue. Do any of you have an opinion on the Delvac for our 19+ 6.7's?
 
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A 10w cold rating is fine for 30 degree temps and a 40 weight is not “too thick” at operating temps. You’d want a 40 weight in a warmer climate anyway. The 40 weight will have a higher HTHS value as well, which is beneficial in a diesel engine, especially when towing heavy. Head on over to Bob is the oil guy forum and spend some time reading about oil. Use this link and provide the necessary data ( KV40 & KV100) and you can graph your oil options and see where they stand at differing temperature ranges. You can find the KV40 and KV100 on the oil manufacturer PDS. Hope this helps you better understand oil. https://www.widman.biz/English/Calculators/Graph.html

Additional info for you: https://bobistheoilguy.com/motor-oil-101/
 
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I live in AZ where I deal with hot as well as freezing cold temps, so I use the T6 5w40. Don't over think it, just go by the owners manual spec's and use what weight you feel best for your location, you'll be good with warranty as well.
 
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I agree that under all the ordinary conditions (cold, hot, towing, etc) the 5w40 is best, and that's what's in my truck now. I'm ONLY thinking about the lifters. Since nobody, including Cummins or Ram, seems to know exactly what's causing lifter failures (or at least, they ain't sayin), I'm just thinking of possible causes and maybe, hopefully, avoiding them. Obviously OCI has been discussed as an issue, and I think most agree that 15k miles is simply too long to wait between changes.... especially with the regen/fuel dilution concerns. Also it's known NOT to use 15w40 oil in these engines for exactly the reasons I'm considering the 5w30, which is to keep the viscosities on the "thinner" side without sacrificing wear protection too much. So just as a possible added layer of protection I'm considering the 5w30 oil and 5k OCI. I dont want to be a lifter statistic.
 
ErikTheRed said:
I agree that under all the ordinary conditions (cold, hot, towing, etc) the 5w40 is best, and that's what's in my truck now. I'm ONLY thinking about the lifters. Since nobody, including Cummins or Ram, seems to know exactly what's causing lifter failures (or at least, they ain't sayin), I'm just thinking of possible causes and maybe, hopefully, avoiding them. Obviously OCI has been discussed as an issue, and I think most agree that 15k miles is simply too long to wait between changes.... especially with the regen/fuel dilution concerns. Also it's known NOT to use 15w40 oil in these engines for exactly the reasons I'm considering the 5w30, which is to keep the viscosities on the "thinner" side without sacrificing wear protection too much. So just as a possible added layer of protection I'm considering the 5w30 oil and 5k OCI. I dont want to be a lifter statistic.
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My 19 I go 15kmiles 5w40 the last change I ended up at 21k before I got the chance to change it. My lifters are quiet no noise many people go the 15k miles with no noises even high millage hot shotters. Not all engines will see lifter issues I am convinced its a machining issue so if you are going to have lifter issues nothing you do will change that.
 
H3LZSN1P3R said:
. Not all engines will see lifter issues I am convinced its a machining issue so if you are going to have lifter issues nothing you do will change that.
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Yeah, I think I mostly agree with that. Some trucks are just gonna have lifter issues, period. But I'm more than just a bit neurotic with this crap so I always WAY overthink everything and I'm always convinced the sky is falling. I'm just doing what I can to minimize the risks. While my cockamamie 5w30 oil theory may be meritless, I KNOW there are healthy benefits to more frequent oil changes.... maybe not financially healthy, but good for the engine.
 
ErikTheRed said:
I agree that under all the ordinary conditions (cold, hot, towing, etc) the 5w40 is best, and that's what's in my truck now. I'm ONLY thinking about the lifters. Since nobody, including Cummins or Ram, seems to know exactly what's causing lifter failures (or at least, they ain't sayin), I'm just thinking of possible causes and maybe, hopefully, avoiding them. Obviously OCI has been discussed as an issue, and I think most agree that 15k miles is simply too long to wait between changes.... especially with the regen/fuel dilution concerns. Also it's known NOT to use 15w40 oil in these engines for exactly the reasons I'm considering the 5w30, which is to keep the viscosities on the "thinner" side without sacrificing wear protection too much. So just as a possible added layer of protection I'm considering the 5w30 oil and 5k OCI. I dont want to be a lifter statistic.
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You may end up being a “lifter statistic” regardless of which of the two approved viscosities you choose to use.

The oil has very very little to do with the lifters failing in these trucks. Aside from a handful of people who refuse to follow the manufacturer recommendations and selected 15w40 in extremely cold environments.

Component quality is the very heart of the problem. The subcontract parts suppliers being utilized to provide the lifter bodies and the rollers for this current valvetrain are producing substandard components that are actually, in some cases, wildly out of spec.

Wether your lifters fail or live a long healthy life will be greatly attributable to your luck, and when your truck was manufactured.
 
Hard to believe that Cummins or Ram would allow it. I understand a "bad batch" getting thru quality control and causing problems, but a sustained supply of inferior parts continuing for a span of 5 years and several hundred thousand trucks seems unbelievable, especially since they're well aware of the problem even if they haven't admitted to it publicly. Additionally, since we now know the "new" 2025's will carry over with the hydraulic lifters, are we to expect the inferior parts issue to continue into the new model year?
 
ErikTheRed said:
Hard to believe that Cummins or Ram would allow it. I understand a "bad batch" getting thru quality control and causing problems, but a sustained supply of inferior parts continuing for a span of 5 years and several hundred thousand trucks seems unbelievable, especially since they're well aware of the problem even if they haven't admitted to it publicly. Additionally, since we now know the "new" 2025's will carry over with the hydraulic lifters, are we to expect the inferior parts issue to continue into the new model year?
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They have multiple suppliers for the parts, and have been in an almost constant state of improvement since 2019. They’ve dropped certain suppliers and picked up new ones but that hasn’t necessarily fixed all of the issues. They did pick up a new supplier for 2025, but since the engines aren’t on the road yet, it’s only a guess as to whether or not things will improve. Suffice it to say they are indeed aware of the problems and are actively working to improve the situation.
 
I think on my next oil change I don’t have a problem with 10W-30 Amsoil severe duty. But I think I’m gonna split the difference just to try it. I think I will end up with a 7.5w-35 I believe.
 
Cseybert said:
I think on my next oil change I don’t have a problem with 10W-30 Amsoil severe duty. But I think I’m gonna split the difference just to try it. I think I will end up with a 7.5w-35 I believe.
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I said to heck with it and just bought 3 gallons of T6 5w40, but your idea to mix the weights ain't a bad one....
 
Why would it be a joke, you got all these people crying about 5W 40 causing lifter 10w 30 causing lifter failures, put them both in there and if my lifters fail then we know it’s not the oil. I believe the only difference in the two oils is the viscosity.
 
Oof, ya got me I guess. Won’t see me trying that concoction in my engine. Good luck getting any warranty backing from Ram or the oil manufacturer if it’s determined you mixed oils, even if they are the same oil just different grades. 5w-40 is the best oil hot and cold, I’ll stick with it.

The only oil that’s documented with direct correlation to lifter issues is 15w-40.
 
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