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I see the shelves where I have been buying my Rotella 15W-40 is now inundated with Rotella Synthetic 5W-40. I like the idea of synthetic oil but I question the wisdom of putting that weight oil in my hard working klinker. The back of the container says that it is approved for Ford, Dodge and GM diesels, but it also says to check the owner's manual, which clearly states 15W-40. My truck never sees sub freezing temperatures, but I'm finding this oil on the shelves here in Mesa, Arizona where it never freezes. Should I use it?
 

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I have been using it since new, almost 80k. I change my oil every 10k and have yet to have a problem. We get everything from 10 degrres all the way to 100 here and have never had a problem with it.

DMAXBOB
 

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The "synthetic" dark blue bottle 5W-40 is a group II based oil, IIRC. It's a very good product for the money. It's lower rating is great for people like me who see sub-zero temps in the winter occasionally. You can use it without reservation.

However, if you're staying around the southwest all the time, you have no need to spend the extra money on that stuff. You'll be fine by saving money and getting any conventional 15w-40; choose whatever brand you can find on sale at Wally World or any local auto parts retail outlet. My in-laws live out in Fountain Hills, and I know that I've seen Delo, Rotella, Delvac, Tection Extra, and other quality brand names on the shelves out there in 15w-40 when I last visited.
 

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That's all I've been using for 50K now. No problems.
 

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Again, as previously indicated, the Shella Rotella T "synthetic" is really not a true synthetic, as in Delvac 1 or Amsoil. Thus it does not have the wonderful low pour qualities of a group IV PAO synthetic. Same with the ultra high temperature performance, not even close..
So, ye gets what ye pays for... Great price with Rotella T 'synthetic' but not true 'synthetic' performance..
And yes, the 5W is the "cold" flow rating. It is a true 40W at normal engine operating temperatures..
George Morrison, STLE CLS
(and yes, it is a constant source of irritation for me with oil companies marketing "synthetic" labeled products, all totally legal, yet not with total integrity)
 

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I woudlnt worry about running a good 5 40
 

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Does the 15w have any possible advantages over the 5w ? I know the advantages of the 5w, but what about the 15w ?
 

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Does the 15w have any possible advantages over the 5w ? I know the advantages of the 5w, but what about the 15w ?
I'm no expert, but from all I've read, not likely. The 15W may be less likely to break down as quickly as the greater ranged 5W, but honestly, synthetic does not really suffer from break down in the normal time between oil changes. So my opinion is that unless you plan on running your oil for a long long time (Idk, say 3+ years) and are thus worried that the already long intervals that synthetic offers are not long enough, go with the more adaptive 5W-40 synthetic. It has excellent cold starting lubrication and the same operating temp lubrication as 15W-40.

I think of it like the single weights compared to multi-weights. The single weight is far more stable, but not good at all temps. So it would go to figure that the lesser the range between the weights of a multi-weight would make it more stable. But would you ever realize that advantage in real world use of synthetics? We do in things like air compressor motors that take a single weight synthetic, but the oil isn't changed for years.

Note: I'm sure everything I just wrote is wrong ;-)

Another note: It took me years to learn to appreciate really thin oil. But when you realize oil cannot lube that which it can not get to, the thinner the better as it flows easily at start up and cold temps. At operating temp, it's all the same: A 40 weight is a 40 weight.
 
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