To add a little to this string.
The base stock oil establishes the xW number. So a 5W-30 starts with 5 weight
base stock oil, a 0W-30 starts with 0 weight base stock and a -5W starts with a
-5 base stock. Yes there are some (-) weight oils now. The viscosity modifiers
are added to maintain the properties at the higher temperatures. What these
modifiers are are hydrocarbon strings that at cold temperatures coil up into
balls thus not impacting the viscosity of the oil. As temperatures rise they
uncoil into strings keeping the oil from thinning out more than what straight
weight oil of the second number. That is a 10W-30 oil at 100C will maintain the
same viscosity as 30 weight oil would at 100C. As Jon stated the bigger the
range between the two numbers the more of the modifiers are needed. The down
side is these modifiers wear out and break down over time resulting in the oil
loosing it's high tempersature lubricating properties.
In the long run a 10W-30 is going to loose less of it's high temperature
properties than a 5W-30.
All liquids have change there viscosity with temperature. Here is where
synthetics have another advantage over dino oil, they change less. So a 10W-30
synthetic will require little or no viscosity modifiers to be able to meet the
rating.
Dave Clement
99 SLT+ CC 4x4
In article <dc9oc3$e4j$1@bent.twistedbits.net>, jon@dakota-truck.net writes:
>
>
> "Valentin Garcia" <valentingar@msn.com> wrote:
>
> : Hey gang, I have a question on oil. What does it all mean? Example:
> : 5w30 vs 10w30. I usually put in what's recommended, but why is a certain
> : weight required? I have an 04 4.7L quadcab Ram that takes 5w30, what would
> : happpen if I put in 10w30. Thank you in advance.
> : I know this has probably been covered before so I apologise for the
revisit.
>
>
>
> This can get complicated :-) but basically, the first number
> followed by the w (5w, 10w) tells you what the oil flows like at
> 0C/32F. The "w" stands for "winter", BTW. The second number tells
> you what the oil flows like at 100C/212F. It used to be that cars
> used a "straight weight", for example, 20 weight, 40 weight, etc.
> Nowadays though, viscosity modifiers are used to cause the oil to
> not thin out as much as it heats up, and to allow the oil to flow
> better when cold. A straight 30 weight oil could actually be
> described as 30w30. When at 0C/32F, it flows like a 30 weight oil
> would at 0C/32F. When at 100C/212F, it flows like a 30 weight oil
> would at 100C/212F. This is because it *is* a 30 weight oil, and
> there are no viscosity modifiers in it. However, a 10w30 oil at
> 0C/32F flows like a 10 weight oil would at 0C/32F, but when at
> 100C/212F, it flows like a 30 weight oil would at 100C/212F.
>
>
> The higher the number, the thicker the oil. I think this is where
> some of the confusion comes into play, a 10w30 oil is supposed to flow
> like a 10 weight oil when cold and a 30 weight oil when hot, but we
> all know that as oil gets hotter, it thins out. How can an oil be
> thinner when cold than when hot? The answer is that it can't - as
> explained above, the two numbers are not comparing the oils at the
> same temperature, it is merely saying that 10w30 when cold flows like
> a cold 10 weight and when hot it flows like a hot 30 weight.
>
>
> Getting back to your qustion, a 5w30 and 10w30 both start out as 30
> weight oil, into which different (or more) modifiers are added. So,
> they should perform the same when at operating temperature, but the
> 5w30 will be a little thinner and easier to flow than the 10w30 at
> cold temperatures. Just as an aside, although I just said that both
> oils perform the same at operating temperature, this is not strictly
> true. Because the 5w30 has more modifiers in it than the 10w30, this
> means that, by volume, there is less 30 weight base oil in the 5w30,
> so you're replacing some of the protective oil with modifiers. The
> further the gap between the low number and the high number, the more
> modifiers are reqired, and the more diluted (and weaker) the oil. As
> long as you stick to a decent oil change interval though, the difference
> will probably be negligible. Note that there is also available 0w30.
> 0w30 isn't actually possible, this is merely 5w30 which has additional
> modifiers that allow its pour temperature to be even lower than the
> pour temperature of 5w30.
>
> The easy answer is to check the owner's manual and use whatever
> it recommends. Usually there will be a chart in there, with different
> oils recommended based on the temperatures in which you operate the
> vehicle. Just pick the one that falls into the proper temperature range,
> and go. :-) (Sometimes that might involve using different weights
> from summer to winter; for example a 5w30 in winter and 10w30 in summer.)
> The 5w30 would give you additional cold temperature protection with a
> (probably negligible) reduction in protection overall, but if you don't
> need it according to the chart in your owner's manual, there's no
> reason to use it over the 10w30.
>
>
> Oh, as far as the other part of your question, "why is a certain
> weight required", basically this is a combination of your cold
> start temperatures, operating temperatures, and engine design.
> Newer engines have smaller tolerances, and therefore need thinner
> oils to properly squeeze between through those surfaces to lubricate
> them. Older vehicles required thicker oil because the tolerances
> were a lot looser, and high oil pressure was required to keep enough
> oil in those gaps to do the job. This is why its best to go with
> whatever the owner's manual recommends. The manufacturer knows what
> the tolerances are in your motor, and has already determined the oil
> viscocity which will give the best protection.
>
> --
> -Jon-
>
> .-- Jon Steiger ---- jon@dakota-truck.net or jon@jonsteiger.com --.
> | 1970 Barracuda - 1990 Dakota 'vert - 1992 Ram 4x4 - 1996 Dakota |
> | 1996 Intruder 1400 - 1996 Kolb FireFly - 2001 Ram QC 3500 CTD |
> `------------------------------------ http://www.jonsteiger.com --'
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