Thanks. 5W-40 = thinner oil, more wear, better fuel economy, longer (synthetic) OCI 15W-40 = thicker oil, less wear, worse fuel economy, shorter (conventional) OCI Reference: John Rosenbaum, Chevron ( link ) "The Ford manual says for severe service run 5w-40." Translation: To maintain the same OCI for severe service, use a synthetic oil.

For example, a 5W or 7W fork oil might end up being thicker than a 10W or 15W fork oil, which can make choosing one even harder. What you need to look at is the viscosity index, which provides a measure of how consistent the viscosity of the oil is across a temperature range. The higher the number, the more consistent the oil is.

A decent race oil will take about 10 hours of hard track use and a semi-syntehtic or hydrocracked base stock will last about an hour before the oil begins to lose viscosity. Are 5w and 0w oils too thin? I read on many forums about 0w and 5w oils being too thin. 0w-40, 5w-40, 10w-40 and 15w-40 are all the same thickness (14 centistokes) at 100degC.

The 10W-40 temperature range is slightly more left than that of 5W-30, as you can see in the chart above. The 10W-40 temperature range is -20 to 40 degrees, whereas the 5W-30 oil’s temperature range is -30 to 30 degrees. The difference in these temperature ranges where these oils stay very fluid sums up the difference between the two viscosities.

The Synthetic 5w-40 just says that the 40 weight oil will maintain a 40 weight viscosity down to 5 degrees vs. 15 degrees for the conventional. FWIW, I saw absolutely no difference between Rotella conventional and synthetic excpet about $10/gallon less money in my pocket for the Rotella Synthetic.

The 10W 40 oil is thicker and is thought by many to be more efficient. 15w40 is thicker at all temps vs 10w30.

The BMW brand 5w-40 is a whole lot cheaper than other 10w-50 and BMW doesn't make 10w-50 motorcycle oil. BMW doesn't "make" any engine oil. And, the USA is the only place it sells BMW-labeled oil. In the rest of the world, BMW recommends Castrol.

10W - 40 oil is a little thinner than oil with a grade of say 15W - 50 or 20W - 40/50. In the Philippines it is better to use thicker oil like the 20W - 40/50 because it is hot and you do not need thinner oil that would lubricate at low temperatures. However, this is not the end of the story. We have oils now that are synthetic and mineral based.

The Differences Between 10w40 & 15w50 Motorcycle Oil. 10w40 grade motorcycle oil will hold its performance right up to 40 degrees Celsius (104 degrees Fahrenheit), while the 15w50 grade motorcycle oil will hold its performance up to 50 degrees Celsius (122 degrees Fahrenheit). The number before the W tells you how the oil will flow in cold

In Brad’s case, his 15W-50 racing oil may be too thick to flow quickly enough to fill the spaces between the crank journals and main bearings while the engine is running. The oil won’t form a consistent lubricating film, allowing metal-to-metal contact and wear. His engine was designed specifically to use a lower-viscosity oil, in this case

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^{This is a difference in PCMO 10w-40s and MC 10w-40 blends. If you're gonna do PCMO, do 20w-50 for that reason. If you don't, then do something rated for a gearbox spec. There are some 15w-40s that are close to a 10w-40, and the cost difference is minimal--I am of the belief that it would bring the risk of fretting fatigue down much further.} Falcon991 wrote: True, but what I meant was this: An 85W transmission fluid is roughly equivalent to a 40W engine oil. I'm not sure if a typical 01W or 20W fork oil is the same as an 0W-20 or 20W Rotella is a North American brand. Rimula is their big brand from Europe. Shell US introduced a cheaper, lower performance (yet decent) CI-4 Plus alternative to Rotella here in the US a few years ago. The performance difference between the two was easily seen comparing CI-4 Plus formulations (though Shell is on it's 3rd CI-4 Plus Rimula The first number of a multi-grade oil designates the ability for the oil to be pumped and flow at colder temperatures; the “W” stands for winter. Thus, a 0W oil will be able to flow faster and get to critical engine components better than a 5W or a 10W oil; especially in extreme cold conditions and at engine start-up.

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