I know the fact that Chrysler recommends 10w30 over 5w30 and 5w20 has been mentioned before, however, the reason why hasn't been discussed to any depth.
If a 10w30 and 5w30 are the same viscosity under operating temperature what benefit does the 10w have over the 5w? I know the idea that these engines may run hotter than others has been mentioned, but again, if the viscosity is the same how would a 10w hold up better than the 5w? Given the longevity of use for these engines and the oil recommendation never changing there must have been a technical reasoning.
Chrysler's rec of 10w30 in 3.5l and 4.0l V6s
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I agree there must be something that we dont see. I dont know what kind of engines those are but if they are ones with variable valve timing and other oil related thing it could have a bad effect if you ran a 0-30 over a 10-30. Say for instance the oil pressure sensor that is tied into the vvt if it were could give it undesired readings with a thinner oil relating to timing problems.
It may have nothing to do with the engine and has to do with how much oil they want to sell of what. From being on this forum I believe 99% of all cars can run almost anything and go past the manufacturers warranty period.
Maybe head office looks at the past numbers of how many people that brought their car to the stealer to get it serviced and they could find an average on oil sales and could even get some future predictions with those numbers.
Maybe they got 10W30 cheaper than the 5w30 from the suplier and saw that if they sold a couple hundred thousand services they could save millions. I dont know but im kinda cheesed that i cant put 0w30 in my car until warranty is up. It does have vvt so I dont know the effect of a change if there is any.
even the sound of 10w30 sounds outdated. I would be ashamed to have to put oil in that my dad did. and im not too young myself. 
This may not be directly applicable, but for what it's worth...
The first generation Cadillac Northstar (1993-1997) specified 10W-30 oil, and subsequent versions specified 5W-30 oil. A Cadillac powertrain engineer used to frequent a few of the Cadillac boards and this question was raised often. His answer was that the 10W-30 held up better to the older design of the first generation valvetrain (direct-acting bucket type lifters). The 2nd generation Northstar (and later variants) went to roller cam followers, and thus the 5W-30 oil. He said either oil works in either valvetrain type, but they saw more shearing with the 5W-30 oil in the first generation engine, so they specified the 10W-30 grade.
I think the 3.5/4.0L V-6 engines from Chrysler use direct-acting bucket type lifters. The new Pentastar uses roller followers. Perhaps not coincidentally, 10W-30 is used in the 3.5/4.0L engines and 5W-30 is used in the Pentastar.
Maybe Chrysler is holding on to old beliefs and info? Or maybe they think 5W30 offers little advantage in cold cranking even well below zero than 10W30. There was a time a few years back that 10W30 was more sheer stable and had less volatility than 5W30. 10W30 may have had less VII. I know that GM recommended 10W30 over 5W30 up till the late 90's and early '00s in some engines and later switched to 5W30 without making any significant engine changes as the oil performance spec increased.
But now it seems the 5W30 has the same voltility and sheer stability as 10W30 and may have base stocks blended with a higher viscosity index.
I use to prefer 10W30 especially in Summer for the reason mentioned, but now I believe the latest 5W30 has no disadvantage to 10W30. And it's geerally a higher quality motor oil.
It's not additives or hot viscosity, and the thinner cold viscosity is better with 5-30.
So it must be like the engineer said - something about stability and shearing.
The Mopar 3.5L SOHC engines as found in my 300M and Intrepid ES are very good engines. Both of mine are tight after a steady diet of 5W-30. This winter for the first time I switched both over to M1 0W-30 since they both sit outside now. I only wish the minivan 3.3 was as good. It seems to be coming apart at the seams with leaks everywhere.
10W-30 was preferred over 5W-30 in the 90s. I know this for a fact.
Apparently, EVERYONE (including the people that make the engines) felt - and perhaps correctly so, what with the SG oils of the time? - that a 10W was more "stable" than a 5W, when both oils reached maximum temperature, and the 10W was preferred to "hold" its "30" viscosity, and protect the engine.
That may not be true anymore, but its another reason people like the grade. Same with 10W-40.. starting with a 10 seemed to indicate more "stable" oil.
Nowadays you can get even 5W-50 oil and its ok whereas 20W-50 used to be used, etc etc (though not by manufacturers, just the "preference" that a manufacturer allowed the user to select. Its in the manuals.)
That is odd. Regardless of the reason for specifying 10W-30, Wouldn't a 5W-30 probably carry a bunch of mfg approvals and probably be a "better oil" Is anyone out there trying to make a better 10W-30?
As I have posted a few times, Citgo makes a dino 10W-30, but no dino 5W-20 and 5W-30; they are both semi syns and carry approvals.
My 2004 Jeep 4.0 manual clearly indicates 10w30 is greatly preferred, 5w30 is okay but only in cold temps. That doesn't really make any sense to me, but the old 4.0 I-6 has to have at least a good 30 weight, so I can only think they were concerned about shear when they made the recommendation.
Of course a 10w30 is still thicker than a 5w30, and the good ol 4.0 does tend to like thick.
I can't really figure it out but I have 5w30 PYB in it now for winter and it's running like a champ on it.
Originally Posted By: KCJeep
My 2004 Jeep 4.0 manual clearly indicates 10w30 is greatly preferred, 5w30 is okay but only in cold temps. That doesn't really make any sense to me, but the old 4.0 I-6 has to have at least a good 30 weight, so I can only think they were concerned about shear when they made the recommendation.
Of course a 10w30 is still thicker than a 5w30, and the good ol 4.0 does tend to like thick.
I can't really figure it out but I have 5w30 PYB in it now for winter and it's running like a champ on it.
Originally Posted By: 45ACP
Originally Posted By: KCJeep
My 2004 Jeep 4.0 manual clearly indicates 10w30 is greatly preferred, 5w30 is okay but only in cold temps. That doesn't really make any sense to me, but the old 4.0 I-6 has to have at least a good 30 weight, so I can only think they were concerned about shear when they made the recommendation.
Of course a 10w30 is still thicker than a 5w30, and the good ol 4.0 does tend to like thick.
I can't really figure it out but I have 5w30 PYB in it now for winter and it's running like a champ on it.
Originally Posted By: RamFan
Originally Posted By: 45ACP
Originally Posted By: KCJeep
My 2004 Jeep 4.0 manual clearly indicates 10w30 is greatly preferred, 5w30 is okay but only in cold temps. That doesn't really make any sense to me, but the old 4.0 I-6 has to have at least a good 30 weight, so I can only think they were concerned about shear when they made the recommendation.
Of course a 10w30 is still thicker than a 5w30, and the good ol 4.0 does tend to like thick.
I can't really figure it out but I have 5w30 PYB in it now for winter and it's running like a champ on it.
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Shake a bottle of RP 20W50 and then a bottle of Syntec 5W50. The Syntec feels like water compared to the RP. The 5W is definitely thinner than the 20W at all temperatures.
Originally Posted By: RamFan
If a 10w30 and 5w30 are the same viscosity under operating temperature what benefit does the 10w have over the 5w?
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Originally Posted By: 45ACP
Originally Posted By: KCJeep
My 2004 Jeep 4.0 manual clearly indicates 10w30 is greatly preferred, 5w30 is okay but only in cold temps. That doesn't really make any sense to me, but the old 4.0 I-6 has to have at least a good 30 weight, so I can only think they were concerned about shear when they made the recommendation.
Of course a 10w30 is still thicker than a 5w30, and the good ol 4.0 does tend to like thick.
I can't really figure it out but I have 5w30 PYB in it now for winter and it's running like a champ on it.
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