"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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