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Originally Posted by Elemental
Why is documented in quotes? Do you know what I do for a living?
Also, I would bet that if you did take your engine apart, your cam lobes woudl be under spec. It shouldnt be because...The oil is to protect the metal parts..... If the metal parts are worn, then it isn't protecting them, is it?
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I imagine you are a mechanic. I know I dont claim to be but you will never convince me to run a thin oil. Your logic makes absolutely no sense as you are comparing fords/hondas to rovers. To me if my trail truck has turned 300k and has never been apart, I am doing something right. Also no doubt I expect there to be wear in an engine with 150-175K, you would have to be an idiot if you didnt. Oh yeah and seeing cooper means that it needs new bearings regardless of what your stupid spec sheets say, the next level is hard steel and craters will form which burn into the journal! Oil does more than just slip between the bearings my friend. It also acts as a "shock absorber" between the bearings/journal and you gotta admit a thicker oil flowing at a faster rate is going to be harder to squeeze out of the bearing gap than your 10 weight oil. (of course this all depends on the outside temperature, manufacture recommendations etc) Im willing to listen to your arguments but clearly you are not willing to hear anyone elses point of view. I wont bore you with details but here is another interesting tid bit to read I found online some time ago. Seem pretty logical to me.
Multi viscosity oils are one of the great improvements in oils, but they should be chosen wisely. Always use a multi grade with the narrowest span of viscosity that is appropriate for the temperatures you are going to encounter. In the winter base your decision on the lowest temperature you will encounter, in the summer, the highest temperature you expect. The polymers can shear and burn forming deposits that can cause ring sticking and other problems. 10W-40 and 5W-30 require a lot of polymers(synthetics excluded) to achieve that range. This has caused problems in diesel engines, but fewer polymers are better for all engines. The wide viscosity range oils, in general, are more prone to viscosity and thermal breakdown due to the high polymer content. It is the oil that lubricates, not the additives. Oils that can do their job with the fewest additives are the best.
Very few manufacturers recommend 10W-40 any more, and some threaten to void warranties if it is used. It was not included in this article for that reason. 20W-50 is the same 30 point spread, but because it starts with a heavier base it requires less viscosity index improvers (polymers) to do the job. AMSOIL can formulate their 10W-30 and 15W-40 with no viscosity index improvers but uses some in the 10W-40 and 5W-30. Other multigrade synthetics may not use VI improvers either. The full literature available from the oil company should include this information. Follow your manufacturer's recommendations as to which weights are appropriate for your vehicle.
Viscosity is a measure of the "flowability" of an oil. More specifically, it is the property of an oil to develop and maintain a certain amount of sheering stress dependent on flow and then to offer continued resistance to flow. Thicker oils generally have a higher viscosity, and thinner oils a lower viscosity. This is the most important property for an engine. An oil with too low a viscosity can shear and loose film strength at high temperatures. An oil with too high a viscosity may not pump to the proper parts at low temperatures and the film may tear at high rpm.
Viscosity Index is an empirical number indicating the rate of change in viscosity of an oil within a given temperature range. Higher numbers indicate a low change, lower numbers indicate a relatively large change. The higher the number the better. This is one major property of an oil that keeps your bearings happy. These numbers can only be compared within a viscosity range It is not an indication of how well the oil resists thermal breakdown.
