I used 15w40 Royal Purple all year round in my Dodge diesel in Alaska. 70-80 in the summer, -30 or colder in the winter. Never had a problem. I would plug my truck in once it hit -20 though.

 

http://www.carbibles.com/engineoil_bible.html

http://minimopar.knizefamily.net/oil....html#champion

 

In answer to Mike,

Why not use 0w 40 mobil 1 then ?

https://www.mobiloil.com/USA-English...l_1_0W-40.aspx

In answer to spike,

I "personally" don't do big milages, how ever in saying that, I have done more miles per annum in my Disco than any other car I have ever had. Had it 2 years (just) , bought with 72k on it, its now showing 94k.

We do have a winter and summer here to lol, probably worst case -8°c --> + 38°c (17-100°F for you guys)

So pretty similar climate to be honest, and I would fully expect Mobil 1 oil is capable of lasting up to 15k in your truck.

 

See, I know about the M1 0w-40, but I cant get it locally, and it does not have any ZDDP in it which a flat tappet type engine needs for longer life.
I would use it in the winter time but like I said I cant get it.
I can get 5w-30 Extended Performance which has a higher level of ZDDP, not as high as the oil I use in the summer time, M1 15w-50 Extended Performance.
There is no way in hell I would go 15,000 miles on one oil change.
You know I'm not arguing with you U.P., this is a great discussion.

I have done a little experimentation with my work van which also has a gas V8.
Keep in mind this was all done using dino oil.
5w-30, I go through 1 qt every 2 days.
10w-30 1 qt every 3-4 days
10w-40 1 qt a week
15w-40 1 qt every 2000-2500 miles.
I have the oil changed every 5,000 miles.
So using a lighter weight motor oil in a high mileage engine can result in higher oil usage.
I think that for most people a 10w-40 is a good all around oil to use.
In my old work van, a 2007 Sprinter with the Merc TD5, it came with M1 0w-40 from the factory and that is the oil that has been used in that van exclusively and it is changed every 10,000 miles...that van eats turbos, that oil is way to thin for the application.
A person needs to assess how they use their truck and determine what is the best motor oil for them.
Just my $.02

 

How about Rotella 5W-40 synthetic Spike that has a ton of ZDDP. I'm mulling that or something wacky like Redline 0W-40 or 5W-40. My engine was a bit sludged so I am trying to slowly clean it out.

 

Whatever oil you choose just make sure that you can get it easily and not have to hunt all over town for it.
And in my opinion you still need to use the weight of oil for your application, if you live in Death Valley use a heavier oil, if you live in Fargo then I would use a lighter oil.

 

I guess what I was saying is why use a 5W-30 oil when there is a good cheap 5W-40 oil available that is perfect for our type of engines. Maybe it is just my truck but it never ran well on 30W oil.

 

Again, it depends on what you can easily get.
I cant get a 0w-40 or a 5w-40...not unless I want to pay out the a$$ for it, and I wont do that.

 

I saw the Rotella 5W-40 synthetic at walmart the other day.

 

That is exactly why I am using Mobil 1 instead of Royal Purple. Royal Purple has become a lot easier to find but still not as common as Mobil 1.

Now when I go back home to Alaska in a couple months I'll have a good, convenient source for RP again ad probably switch to that once I win the lottery or get awarded a huge settlement for spilling coffee in my lap.