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February 5th, 2004 02:55 AM #12VI- can also mean viscosity index, which measures the length of time for the oil to break down. Most single grade oils are below 100 while multi-grades are at 130+. Synthetic oils start at about 160+.
The other component of newer oils is the additive package wherein a higher API rating usually means better additives. These additives protect the base oil from soot, acids which, inevitably shorten the life of a diesel oil.
The mobil site (www.mobil.com.au) has a lubrication guide for most cars/suvs, almost all use a multi-grade oil- australia has extremes in temp, like 40deg summers.
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February 5th, 2004 09:32 AM #13Viscosity index is really the ability of an oil to maintain its thickness or thinness(viscosity) over a WIDE temperature range.
It has nothing to do with lubricating abilities. The index is more usefull for temperature climates where huge temp swings are normal year round, say 20 deg F to 90 F year round. The higher the index the better for these locations.
At 212 F(100 Centigrade) engine temps 5W30 10W30 Straight 30
oils have the same viscosity, they are the same oil. PAg malamig lang nagkakatalo! Ngayon, pag 30 degress F na ang weather dyan matatalo ang straight weight oil. Like I said in earlier post
when do we get 30 degree weather in RP?
Kaya ko lang gusto ang straight weight sa hotter running engines like turbodiesels is that at higher viscosities (straight 40 or 50 it withstands heat a lot better and wala syang halo na viscosity improvers which tend to break down in high heat.
BTW Australia is known to be a hot place, your right, but they use multigrades there because it also gets real COLD in a lot of places BRRRRRR
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February 7th, 2004 09:03 PM #14ezgrand
So what oil do you actually use? In what application, engine? What's the Api/Acea rating of the oil?
Have you ever done a used oil analysis locally to determine viscosity at both 40 and 100deg, TBN, VIndex, insolubles? I have on a multi grade 5w30 synth oil.
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February 11th, 2004 07:22 PM #15Jack, I use Mobil or Caltex straight weight 40 on my Toyota 2LTE. I've also used it on Mistubishi and Toyota engines for 10 years without any problems. As I mentioned viscosity improvers are just that viscosity improvers that do nothing to help lubricate an oil better in a tropical country where the temps don't really fluctuate.
BTW I think you are kinda confused regards viscosity which is really comes into play in AMBIENT temps! how can I test my oil viscosity at 40 deg F when our temps in Manila never go that low!
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February 12th, 2004 12:08 AM #16ez,
The tests done measure viscosity at 40 and 100 deg C so they show what happens within an engine. Think that the performance of an oil at normal working temps of an engine matter more than ambient temps. A turbo adds stress on the oil, just as high sulfur fuel, egr's, soot. Used oil specs would give you an idea if the oil can handle all these factors.
If the oil were to breakdown then you form a sludge which can ruin an engine. This sludge can be prevented by the use of the right additives, which i think you call viscosity improvers, or better base oils.
I do not doubt that the sae40 works but i too have used multi grades for more than 10 yrs and have never had problems.
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February 12th, 2004 12:14 AM #17Jack, thanks for the info! Noted! My original posts were just meant to explain that the lower numbers in a multi grade oil is meant for real cold weather and that "W" stands for winter.
just wanted to stress that straight oil is good enough for the tropics! my humbel opinion.
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February 12th, 2004 09:45 AM #18ez,
This is from an article on synthetic oils, and what lower viscosities do for an engine. Hope this helps.
Quote:
It is also important to note that, contrary to what many take for
granted, higher viscosity in and of itself does not translate into better
engine protection. Extensive testing has shown the opposite to be in
fact true. As long as a lower-viscosity oil is formulated to resist
evaporation and provide high film strength, this lighter oil will
actually deliver more complete protection to the engine parts, since its
more rapid circulation delivers both better lubrication per se, and far
better cooling characteristics...a critical advantage, given that oil
flow furnishes up to 30% of an engine cooling requirements. Prior to
the introduction of synthetics, however, the problem of evaporation (and
the resultant thickening of the remaining oil) was addressed primarily
by increasing viscosity. In short, don't be concerned with the
relatively lower viscosity ratings of some synthetics. Syn lubes are a
whole new ball game.
Quote:
Viscosity is a crucial consideration when improvements in fuel economy
are desired. It stands to reason that the freer and engine turns, the
less fuel it will require to accomplish a given amount of work. Studies
have demonstrated conclusively that engine drag is directly related to
the viscosity of the motor oil. Generally speaking, the lower the
viscosity, the better the fuel economy of the engine. In formulating
lower-viscosity oils, it has become clear that synthetics are the base
stock of choice. This is because it is possible to produce a synthetic
oil of a given low viscosity without incurring the excessive oil
consumption (due to evaporation) and resultant thickening of the same
low-viscosity petroleum oil.
Quote:
High temperature
stability, as well as oxidation-resistance, is of absolutely paramount
importance when it comes to turbocharged engines. Because it must both
lubricate *and cool* the turbo unit, the oil MUST be specifically
formulated to withstand the turbo's extremely high operating
temperatures. Oil film temperatures often exceed 450F in the turbo unit
during operation, and can surpass 650F(!!!) during a short period
immediately following engine shutdown...both figures far exceeding the
thermal limits of petroleum oil. Synthetics, with their capacity to
maintain proper (low) viscosity and lubricity under these high heat and
stress conditions, and with their natural resistance to oxidation, have
risen to the fore. It is also important to note that the
high-temperature-stability properties of synthetics are *designed
primarily into the base-stock oil itself*, rather than being achieved
primarily with additives.
That is the reason why I travelled with my family whenever their is an opportunity when the kids...
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