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[QUOTE="Jaybird, post: 1227061, member: 22283"] If our temps were constantly within a certain range, say like 60f-90f all the time, then we would probably be best using a straight wt. oil such as sae 30-40wt. The reason being that there are no additives to manipulate the viscosity. The base oil used is essentially the same weight as the finished product. A multi-grade oil starts out using a very thin base oil that will also have a low pour point temperature. This is anticipation of the startup in winter temps. We need to oil to flow as fast as possible when we start the engine, and without the oil having the ability to flow quickly to the critical points of the engine, wear can occur until it does get there. There may be only a small amount of wear metals created during the few strokes the engine makes before it starts, but this is when the engine is most vulnerable. The majority of an engines (normal) wear is created during startups. So a 5w-40 oil will be built using a base that has a viscosity of 5wt, and has viscosity improving polymers added that will allow the oil to thicken to a 40wt at operating temps. The problem is that these viscosity changing polymers are very vulnerable to being sheared down from mechanical action. Picture these polymers as little coils that get unwound with use. Once these polymers are "unwound" from shear, they loose their effectiveness. The greater the spread in numbers of a multi-grade oil, the more of these polymers that have been used to accomplish the task...and oils with high amounts of viscosity improver's may well perform as other oils when new, but shear down faster than an oil with a lesser spread of numbers. A 5w-40 is generally less shear resistant than a 15w-40. But this is just a rule of thumb... The base oil used has lots to do with this issue. Synthetic base oil is much better at handling temp swings than mineral oils. There isn't the need to use the vulnerable polymers when using a synthetic base, so synthetics are far more shear resistant than mineral oils. Just about any 5w40 oil you find on the shelf will be formulated using group III oil. Group III oil is coined as a synthetic, although it is actually conventional petroleum oil that has been processed to a point that it is as near to coming out of a lab as true synthetics, like POA and esters, are. (Albeit they aren't created in a lab or a magicians hat either, and are derived from petroleum and organic products as are mineral oils) Some new process' refiners have developed for making group III oil are producing fantastic products for far less production costs than their PAO and ester counterparts. Especially Shell's grp III bases oils, imo. These grp III oils are also showing to have equal or near equal prowess with cold weather startups as PAO and ester base oil. Using a 5w-40 of any flavor is probably going to be all the cold weather riding protection one would ever need in any 4T dirt bike. It would also be a fine choice for the 2T, however we don't have the immediate flow problem we worry about at start of the 4T. A straight weight lubricant is all that is really needed in the clutch box. That is one of the reasons I use ATF in a 2T, which is very heat and shear resistant, and thin enough to perform well at colder temps with nil viscosity additives. [/QUOTE]
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Switch Viscosity For Weather?
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