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OIL
Posted by : WiganBob (188.220.190.27) 
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On Tuesday 14/08/12 at 14:06:07
Been doing a little research on oil operating temperatures. The following makes interesting reading. I think I read this a few years ago but its worth reading again,
To make a 10w-40 oil, the manufacturer would start out with a 10 weight oil as the base stock. All by itself, this oil would thin out so much at normal operating temperatures that the oil film would be useless. So, they add these very special very long molecules, the VIIs. The VII molecules are as much as 1000 times as long as an oil molecule. The VII molecules curl up in a little ball at room temperature, but as the temperature gets higher they uncurl and stretch out, like a cat sleeping in the sunlight. The more stretched out the molecule is, the more it impedes the normal flow of the oil, thus raising the effective viscosity. Now, this sounds just a little too good to be true. Well, there are two catches: first, these molecules are not lubricants, so the more of them that you add the less oil you have sitting around lubricating things. Secondly, these VII molecules can be broken into pieces by various pressures and forces, like being squeezed through the transmission gears in a motorcycle or the hydraulic valves in a diesel engine. Every time a VII molecule gets broken, the oil loses some of its high temperature viscosity. Synthetic oils made from pure PAOs and/or Diesters typically have very few VIIs, so these oils are far less subject to viscosity breakdown due to shearing of the VII package. As a result, synthetics are far more stable in a motorcycle engine.
10w-30 oil increases its viscosity at high temperatures by a factor of three, which requires a significant amount of these VII molecules. 10w-40 oil increases its high temperature viscosity by a factor of four, which requires even more even longer molecules. 20w-50, which sounds a lot like 10w-40, only increases its high temperature viscosity by a factor of two and a half, so it requires fewer of these molecules than even 10w-30. 15w-40 also increases its high temperature viscosity by about two and a half, so this oil is also substantially more stable than 10w-40. Most passenger car oils today use inexpensive VII molecules that break apart relatively easily. Conversely, most diesel engine oil VIIs are chosen from more expensive chemicals that are more shear stable, since an oil change in a large diesel is expected to last for 15,000 to 150,000 miles.
One way to judge the VII content of your oil is to read the VI, the Viscosity Index, at the manufacturer's web page. The base oils all have similar VIs to start with, so generally speaking, the higher the VI in the blended oil, the more VIIs are present, and the less suitable the oil is for motorcycle usage. John Evans did just such a survey of Valvoline, Chevron, Exxon, Quaker State, Citgo, and Conoco oils. He found that the 5w-30 oils all had VI's in the range of 158-162; the 5w-20 oils had VIs of 148-154; the 10w-40 oils had VIs of 147 to 150; 10w-30 oils had VIs of 134 to 139; and 20w-50 oils had VIs of 120 to 125.
In 1994, Dr. John Woolum tested the viscosity of several 10w-40 oils in his motorcycle. He found that all of the petroleum oils had lost highly significant amounts of viscosity within 1500 miles. Only Mobil-1 held up in his test. I have personally tested Delvac-1 synthetic in my ST1300. It was 5w-40 when I put it in, and 5w-25 9,200 miles later. By 1500 miles, the petroleum oils Dr. Woolum tested were at 10w-25 equivalent. By contrast, Dr. Woolum tested a petroleum oil in his Honda Accord. After 3600 miles, the 10w-40 oil was 10w-37 equivalent. Motorcycles are indeed significantly harder on their oils than cars. Based on this result and the VI numbers above, it would seem that 10w-40, 5w-20, and 5w-30 oils cannot be safely used in motorcycles for more than 1,000 to 1,500 miles.
This is an exert from http://motorcycleinfo.calsci.com/Oils1.html 
Message Thread:- OIL - WiganBob Tue 14/08/12 at 14:06:07
- RE: OIL - Kebob Tue 14/08/12 at 15:38:12
- RE: OIL - Harry Notts Tue 14/08/12 at 16:14:29
- RE: OIL - Ady - near Rhayader Thu 16/08/12 at 13:14:03
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