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.

[IdaD]

I run 5w40 synthetic but I think 15w40 is fine in most climates. I just tend to run into cold weather in the winter months so I like the colder weather protection. Rotella T6 is what I generally use. FWIW my father lives in a similar climate and has run conventional 15w40 for years in his 7.3 with no issues so either is probably fine for most applications.

[Walaby]

BurbMan wrote:

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*,

Think you answered your own question.

Since you asked, I use 15W40.

Mike

[blofgren]

I used to run 15W40, but for the last couple of years I've been buying complete service kits from Cummins online which includes premium Fleetguard filters (fuel and oil) and Valvoline Premium Blue Extreme full synthetic 5W40. The engine does seem to be a bit quieter with the Valvoline, but I think either is fine.

Here is the kit that I buy.

[ppine]

Follow manual. Simple.

[ShinerBock]

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.

[BenK]

IMHO...depends on how hard you plan to drive it...

I'd go higher viscosity

[ShinerBock]

There have been hundreds of thousands of Cummins owners that have gotten hundreds of thousands of miles out of their truck running regular 15w40 even in colder climates. Not saying that running 5W40 is bad or not needed, but most who do only do it for "cheap insurance" because they "feel" that it will extend the life of their engine. How long while it extend the life of the engine? They don't really know, but it makes them feel better.

Could be that 5w40 extends the life of the engine an extra 10k miles or 100k, but if you are only keeping the truck for 300k miles and 15w40 will easily get you there then what is the point of spending extra money on something that will extend it past that? You are just spending extra money that will only benefit the next owner.

Basically, most(not all) are doing it based on emotion rather than actual data or need. Some do actually need to run 5w40, but most do it because makes them feel better that they are doing a good thing extending the life of their engine. Not saying this is bad thing because a lot of people(including me) spend lots of money on things that make them feel better, like beer :B......

[Cummins12V98]

100% run 15-40. If it's synthetic the pour point is not much higher than the 5-40.

[BurbMan]

This is what the owner's manual says:

[Lwiddis]

Follow Ford’s recommendations. My gas Chevy is 0W20. Light stuff!

[SweetLou]

15-40 should be just fine

[DownTheAvenue]

I am always in favor of doing what the owner's manual, written by the people who designed and built your vehicle, says to do rather than people on an internet forum say to do.