5W40 or 15W40 in 6.7 CTD?

[BurbMan]

So the owner's manual in my 2015 Ram says to use 15W40 oil in the 6.7 Cummins diesel, unless the temp is going to routinely be below 0*, in which case you should use 5W40.

Here on Long Island, the temp rarely if ever even gets to 0*, much less stays under it for any period of time. I'm coming up on my first oil change since I've owned the truck, and I was all set to stay with 15W40. However, guys on a couple forums are saying they use 5W40 year round.

Please let's not get into a brand war or discussion about dino vs. synthetic, but I'm interested to know what weight oil you guys are using.

[otrfun]

LIKE2BUILD wrote:

otrfun wrote:

LIKE2BUILD wrote:
. . . Another point for me is oil change frequency. The manual says to change oil every 15,000 miles or 500 hours and I don't even come close to that mileage in a year. So, I just change my oil once a year and with the 5W40 I'm covered for any temperature range and I don't have to worry about it.

KJ

Our 2016 Ram Cummins OCI is 15,000 mi., 500 hours, or 6 months, whichever comes first. Your profile says you have a 2014 Ram Cummins. Is the OCI different for the 2014's?

You're right, it does say 6 months. However, I'm comfortable with the additive packages in the synthetic oil and use the 1 year time frame. When I changed oil this summer I had only put 5,200 miles on the truck since July of 2019. If I would have changed oil at 6 months it would have been less than 25% used (on a mileage basis).

KJ

I was just curious, thanks. We have an 8y/120k OEM extended warranty, so we'll be sticking with the 6 mo. OCI for a few more years/miles. If we still have the truck after 8/120 we'll probably go to a 12 mo. OCI using 5w-40.

With that being said, gotta wonder which would keep my Cummins runnin' the longest? 15w-40 changed every 6 mo. or 5w-40 changed every 12 mo.? lol! 🙂

[FishOnOne]

ShinerBock wrote:
There is not much difference in a used oil analysis between 15k oil at a year and 15k oil at 6 months. The detergents and other compounds in the oil is slightly less, but still well within spec. In fact, it would be next to impossible to tell the difference between the two.

Some like to error on the side of caution because they do not know any better, and I get that. If you have never performed a UOA to know exactly how oil holds up, then by all means change it every 6 months if it makes you feel better and is "cheap insurance" to you. I, on the other hand, would rather know and have hard data when making such decisions. I change it once a year because I know there is no significant difference between the two time frames based on UOA's from my own truck and the thousands of 6.7L Cummins engines we perform UOA's on at work.

The 6 month oil change is probably to cover for B20 diesel, short commute and town driving.

[time2roll]

How about compromise with 10W40? Go ahead and mix the two if needed.

[LIKE2BUILD]

otrfun wrote:

LIKE2BUILD wrote:
. . . Another point for me is oil change frequency. The manual says to change oil every 15,000 miles or 500 hours and I don't even come close to that mileage in a year. So, I just change my oil once a year and with the 5W40 I'm covered for any temperature range and I don't have to worry about it.

KJ

Our 2016 Ram Cummins OCI is 15,000 mi., 500 hours, or 6 months, whichever comes first. Your profile says you have a 2014 Ram Cummins. Is the OCI different for the 2014's?

You're right, it does say 6 months. However, I'm comfortable with the additive packages in the synthetic oil and use the 1 year time frame. When I changed oil this summer I had only put 5,200 miles on the truck since July of 2019. If I would have changed oil at 6 months it would have been less than 25% used (on a mileage basis).

KJ

[Learjet]

Edd505 wrote:
Rotella T6 and never worry

yep...and you can get T6 now in 15W-40

[ShinerBock]

There is not much difference in a used oil analysis between 15k oil at a year and 15k oil at 6 months. The detergents and other compounds in the oil is slightly less, but still well within spec. In fact, it would be next to impossible to tell the difference between the two.

Some like to error on the side of caution because they do not know any better, and I get that. If you have never performed a UOA to know exactly how oil holds up, then by all means change it every 6 months if it makes you feel better and is "cheap insurance" to you. I, on the other hand, would rather know and have hard data when making such decisions. I change it once a year because I know there is no significant difference between the two time frames based on UOA's from my own truck and the thousands of 6.7L Cummins engines we perform UOA's on at work.

[noteven]

When receiving money saving advice on a once or twice a year maintenance...

I kinda nod politely while thinking: "So, like, if I don't eat out 3X in the next year I could afford top quality oil and filters for my replacement cost $70,000 pickup then?"

[Grit_dog]

otrfun wrote:

LIKE2BUILD wrote:
. . . Another point for me is oil change frequency. The manual says to change oil every 15,000 miles or 500 hours and I don't even come close to that mileage in a year. So, I just change my oil once a year and with the 5W40 I'm covered for any temperature range and I don't have to worry about it.

KJ

Our 2016 Ram Cummins OCI is 15,000 mi., 500 hours, or 6 months, whichever comes first. Your profile says you have a 2014 Ram Cummins. Is the OCI different for the 2014's?

Well since his truck is OUT of warranty, no need to feel the obligation to stick to the ridiculous 6 month OCI.

[Edd505]

Rotella T6 and never worry

[blofgren]

I changed my oil twice per year while my truck was on warranty; I only change it once per year now that it's off warranty. I don't drive it as much as I used to since I bought an older Yukon to pull our boat.

[ShinerBock]

Now that I only drive my truck about 15k miles a year, I only change it once a year as well. I never understood why Ram chose to go 6 months. In other on highway applications that have 15k mile intervals, Cummins recommends 12 months for the 6.7L. It is only the low speed and constant stop/go applications that they recommend 6 months. I guess Ram wanted to be on the safe side.

[otrfun]

LIKE2BUILD wrote:
. . . Another point for me is oil change frequency. The manual says to change oil every 15,000 miles or 500 hours and I don't even come close to that mileage in a year. So, I just change my oil once a year and with the 5W40 I'm covered for any temperature range and I don't have to worry about it.

KJ

Our 2016 Ram Cummins OCI is 15,000 mi., 500 hours, or 6 months, whichever comes first. Your profile says you have a 2014 Ram Cummins. Is the OCI different for the 2014's?

[LIKE2BUILD]

BurbMan wrote:
This is what the owner's manual says:

I went down the same path wondering which to run when I first got my Ram. The easy answer is run synthetic 5W40 since the arrows point to infinity in each direction. When I first got my truck I went to my local dealer for some Jeep parts and while there asked them which oil they use for servicing Cummins engines. The guy turned around and pointed at stacks of Rotella T6 5W40 on the shelf and told me that's what they put in every single 6.7L truck. I know, DEALER can be a 4-letter word, but if they are using this oil for trucks under warranty then I'll go with it.

Another point for me is oil change frequency. The manual says to change oil every 15,000 miles or 500 hours and I don't even come close to that mileage in a year. So, I just change my oil once a year and with the 5W40 I'm covered for any temperature range and I don't have to worry about it.

KJ

[BurbMan]

Thanks for the responses and think I'll be fine with the 15W40. Going to order this kit from, Cummins online store.

[BenK]

Thanks and know that chart but it is not the hot end that I’m most interested in.

Film strength is the biggest component specification am in interested in.

As I believe in the articles over many decades referencing that most of engine wear is due to dry starts. Mostly after extended times off, like over night or a few days.

Too many will just shut off their ICE after driving HARD. I allow mine to cool down before shutting down after driving hard. Around town, sure just shut it off, as my ICE doesn’t get up there in temp just driving around town.

Which reminds me...time to replace the severe duty fan clutch, as it doesn’t couple as high as it used to. Know because it doesn’t ROAR anymore.

Am after the highest film strength keeping as much of an oil film as possible and believe higher viscosity of the lower number helps solve that issue.

ShinerBock wrote:

BenK wrote:
IMHO...depends on how hard you plan to drive it...

I'd go higher viscosity

Both have the same viscosity grade of 40 at operating temp so they are about the same when driven hard with 15w40 having the slight edge. It is their cold temp viscosity grade that is different which mainly only comes into play when the oil temp is below 30F. One has a cold viscosity grade of 5W and the other 15W.

Snip....