5W-30 and 10W-30

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May 29, 2004
I'm having this discussion on another board. Is there any truth to this:


METhe 30W is the same regardless so stability will be the same when the engine heats up. 10W will just give some extra protection during startup, but not much over a 5W.


Other posterIt's not the same. Being a 30 wt. at temp isn't where the extra stability I'm talking about comes in. The spread between 5W and 10W when cold, and the different chemistry's used to achieve it are the reason why one oil is more shear stable than the other. Even though they both meet the requirement to be called a 30 wt oil at 100c, there are still differences in how the oil will behave at temp. over the drain interval.

I thought that the only difference between a 5W and a 10W in a dino was the start up weight. Someone enlighten me.
If you assume that most relevant variables are the same or close, he's got you on this one. The 5w oil started as a thinner oil and will require a larger dose of viscosity index improvers (VII) to make it behave as a 30 wt when hot. The inability of these VIIs to perform consistently over the life of the oil is perhaps the major contributor to the phenomenon of viscosity shearing down to a lower level. Now, the closer you get to a "perfect" shear-proof oil, the more correct your statement becomes. High quality synthetics, with naturally high viscosity indexes are probably the closest you can get to this level of perfection.
If your speaking of low cost dino's the big difference is most 5w-30's will use mucho more group II than it's 10w-30 brother . The group II usually being a very light base oil with better cold performance by nature .

This effectively allows for less or same VII's with the larger spread in some engine oils dispelling a common myth floating around and the benefits of more group II than group I in a given base blend should be obvious .


I should add an oil with more group II in it should also be able to use less pour point depressants and alter cloud point as well .

Key is knowing who is using what in terms of base oils and if in doubt use a blend and remove all doubt about what your getting even if the synthetic portion is group III

[ June 30, 2004, 07:54 AM: Message edited by: Motorbike ]
Interesting. You learn something new every day. Guess I've been around synthetics too long. Thanks guys.
I think if you compare some of the grades within a brand you will find the 5w30 made with better base oils than the 10w30, so in many cases it may be somewhat compensated for the wider spread. For example, look at Valvoline Durablend:

Grade / CAS 64742-54-7 / CAS 64742-65-0

5w30 / 54-64 percent / 10-20 percent
10w30 / 23-33 percent / 51-60 percent

So the 5w30 has a whole lot more of the Group II,II+,III CAS ##, whereas the 10w30 has a whole lot more of the Gp I(?).

For Durablend the 5w20, 5w30, and 10w40 are similar with high levels of the Group II,II+,III; whereas the 10w30, 15w40, and 20w50 with the tighter spreads all have higher levels of the GP I.
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