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Old 02-20-2013, 10:40 AM   #15946
Beastly Adventurer
Joined: Jul 2008
Location: Meadowlands, NJ (just east of the USA)
Oddometer: 2,119
Originally Posted by fbj913 View Post
to me this is an old way of thinking. oils have temperature ranges these days. a good 10w-40 will work as described as long as you stick to the correct temperature ranges described by the manufacturer. i would say most synthetic oils are good into the negative temperature ranges (def F). also companies like Amsoil say right on the oil that the 10w-40 will work for a variety of different oil needs... although this may not be true for all companies and can vary between synthetic and standard. this discussion is very much less important when talking about Synthetic! just stick to what the motor or manual says. it doesn't pay to over think when it comes to oil. old habits die hard!!! especially oil habits. even when its hot outside its best to let the bike warm up before you ride it. same goes with cold temps, it will just take longer.

AMSOIL Synthetic 10W-40 Motorcycle Oil is recommended for liquid or air-cooled 4-stroke engines. It meets SAE 80W/90, API GL-1 gear oil requirements and is recommended for transmissions on both 4- and 2-stroke motorcycles. AMSOIL MCF is recommended for Honda®, Kawasaki®, Yamaha®, Suzuki®, BMW®, Husqvarna®, Victory® and other motorcycles where 10W-40 or 20W-40 engine oils or SAE 80W/90, GL-1 gear oils are used. Not recommended where an API GL-4 or GL-5 gear oil is required.

i hate oil discussions. its way to opinionated!!!
But I wouldn't run it regularly in a motor that called for xW-30 weight oil, unless I had a very specific reason to, because the second value is what's important once up to temp, and where your motor spends most of its time. A 40 would be less viscous in a warm motor. Running a oil with a slightly higher cold viscosity (lower first number) just means that it flows easier when cold, but will 'thicken' as it warms.

The viscosity will determine how easily the oil is pumped to the working components, how easily it will pass through the filter, and how quickly it will drain back to the engine. The lower the viscosity the easier all this will happen. That is why cold starts are so critical to an engine because the oil is cold, and so relatively thick.
But, the lower the viscosity, the less the load the oil can support at the bearing on the crankshaft. The higher the viscosity, the better the load it can support. Even this, however, has a trade-off, since the higher the viscosity, the more the drag at the bearing, and hence, potential power loss, or increased fuel consumption. So a compromise is chosen to minimise power loss, but maximise load support.
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