change from 15w 40 to 5w 40 oil

[jp45601]

I have a 04 6.0 with 167,000 miles on it. My owners manual says to use 15w 40. Could I change from 15w 40 to 5w 40 synthetic oil. If I do, would there be any problems resulting from switching over?

[RRSA]

No problems and your truck will love it.

[jp45601]

Thank you for the quick reply. Come spring I will be changing over to 5w 40 synthetic oil. I would change over now but I just did a oil change for the winter.When I change over I will be running 5w 40 year round.

[Gearhead2012]

Yeah, for the most part the old misnomers about how synthetics make your engine leak and burn oil are false... but if you're engine leaks or burns oil now, typically they'll get slightly worse (at least from my experience). There's also a lot of decent sythetic blends out there now too... which part of me thinks might be better for the engine as a whole, but the injectors for sure will prefer the sythetic. Breaking an engine in on a synthetic is generally accepted as bad practice...which makes me wonder, why are synthetics better after it's broken in...I've heard lots of the theories, but I'm trying to educate myself further and find out more scientifically on why.

Sorry for the rambling...when I went with either the T5 or T6 my truck ran better (especially in the winter), and gets better mileage.

[jp45601]

I had the understanding that synthetic oil in a older engine caused tha rubber seals to leak. A lot of people believe that synthetic oil in a new engine will not stick to the sides of the cylinders because there are no score marks on the cylinder walls unless you run the engine with regular oil for at least until after the first oil change.

[Gearhead2012]

Originally Posted by jp45601

I had the understanding that synthetic oil in a older engine caused tha rubber seals to leak. A lot of people believe that synthetic oil in a new engine will not stick to the sides of the cylinders because there are no score marks on the cylinder walls unless you run the engine with regular oil for at least until after the first oil change.

Oh I've heard all the theories. I work at a engine reman shop, not that it necessarily qualifies me for anything, but just that it puts me around this stuff all the time.

Generally, a "score" on a cylinder wall is a bad thing, like a scar. The typical theory is that the synthetic is "too slippery"... and that there's essentially not enough friction for new rings to properly seat on a freshly honed cylinder wall.

Some people used to say that when you switched to synthetic it swelled up your seals, and that if you switched back it would "shrink" them and then you'd develop a leak - or that the "molecules are so small that they'll just leak out everywhere"...

It's all mostly crap, but the molecules are smaller, and more uniform, and because of that, if there is an existing leak, or the motor does have say a valve stem seal that's letting some oil by, or rings that aren't sealing well, synthetic will sometime seep by faster. Even then, the term synthetic is kind of a gray area anyway...as evidenced again in an article posted by PGreensvt in this thread

switching to synthetic oil

which discuses the what could potentially be great oil, even if not derived from what is traditionally revered as synthetic base stock. talks about how castrol syntec changed formula to what's not technically synthetic and mobil sued them and how it all plays out. Great link from Mitch.

I generally think I understand the general point of synthetics, and what they're good at, and bad at... I'm just always on a quest to know why, or how something works the way it does. In this case, it's just very scientific and hard to fight through the marketing jibberish.

Any word on what base stock rotella t5 or t6 is derived from?

[PGreenSVT]

Rotella T5 is a synthetic blend so I am going to guess it is a blend of groupIII and GroupI or II stocks since the T6 full synthetic is a groupIII base with some groupIV and or groupV. of course there are specific additive packages on top of that. The groupIII base stocks are derived from severely hydrocracked crude while groupIV is PAO and GroupV ester based.

I guess that doesn't really make things clearer. What I can say for Rotella T6 is that I have seen numerous very favorable UOA reports from guys that run it and it is readily available.

[trophy_23]

I have only had the truck long enough for 1 oil change, with regular dino oil. Do you guys get synthetic changes done at the dealer? What is their stance on 5w40?

[ak49er]

I believe it has something to do with the material the seals are made of. In older vehicles I own, I have developed leaks after swapping to a synthetic.
But these are from the 70's-'80s.

And my boat motor (460) was assembled in 1974, which leaks now, where it did not before.

Today's "rubbers" are more chemical resistant than before.

Buna-N=Nitrile=Natural Black Rubber

Now you have Neoprene Viton, HYPALON, EPDM, Flourosilicone and other hearty compounds for seals.

[Gearhead2012]

Originally Posted by PGreenSVT

Rotella T5 is a synthetic blend so I am going to guess it is a blend of groupIII and GroupI or II stocks since the T6 full synthetic is a groupIII base with some groupIV and or groupV. of course there are specific additive packages on top of that. The groupIII base stocks are derived from severely hydrocracked crude while groupIV is PAO and GroupV ester based.

I guess that doesn't really make things clearer. What I can say for Rotella T6 is that I have seen numerous very favorable UOA reports from guys that run it and it is readily available.

I had been looking for some reports on it, good to know that it's holding up well... any idea what interval most are changing it at... the standard 5k? I'm still doing a bunch of reading on all of this, but sounds good enough to me... like I said, I'm no chemist, so, group I, II or whatever doesn't mean a whole lot to me, yet. But, it seems like perhaps the t6 might fall into the same category as the castrol syntec did in the article, where perhaps mobil 1 might argue that it's not a true synthetic?

Originally Posted by trophy_23

I have only had the truck long enough for 1 oil change, with regular dino oil. Do you guys get synthetic changes done at the dealer? What is their stance on 5w40?

I've had two local dealerships recomend a lighter weight oil in the winter, although neither had heard of rev-x. I'm still hung on whether it's snake oil, or it works. I've heard lots of hype that it works, more than I have heard of it not working... but still hard to totally think that a simple additive will totally fix a problem like that - albeit a 70 dollar additive. I can say that won't be getting an additional 70 bucks from me per oil change for the rev-x... but I might give it a shot. I wonder if it falls into a group of base stocks?.. lol