Carreful how you explain that. Remember, the first number, the one before the "w" can only be compared to other "w" numbers. You can't truly say that x flows like y at z temp.
I'd also point out that vii's have improved a great deal over time. It's all in the quality of vii that the blender uses. Oils have to meant some pretty exacting standards to be rated API SM and ILSAC GF-4. Additionally, some synthetic base stocks require little to no vii to be multi-viscosity.
Another thing I'd point out just in general to everyone is remember that oil is going to be thinner when hot, regardless. Multiviscosity oil's don't thin as MUCH as a monograde oil would, but most grades do thin. Just pointing it out b/c some people think, from the way that the oil is graded, ie 5W30, that the oil thickens to a 30 weight from a 5. I can't tell you how many times I've heard "That oil was like water when I drained it!" Duh! That's not how the system works. They are two different measurements.
Quote:
Originally Posted by Selden
There has been an appalling amount of mis-information about oil viscosity in this thread. With a multi-viscosity oil, the first number is the actual viscosity of the base oil. Viscosity improvers (long chain polymers) are added to oil to the base oil to prevent it thinning out as much as it it normally would at operating temperatures. Thus the second number is the equivalent viscosity of the base oil at 100 degrees Celsius; that is, a 5w-20 oil is a 5 weight oil that flows like a 20-weight oil at 100 degrees celsius. Unfortunately, viscosity improvers can break down over time (the long chain polymers can be sheared), so as a general rule, multi-viscosity oils may be more subject to shearing as they age than single weight oils. Shearing breakdown is less of a problem with synthetics.
If Honda recommends 5w-20, I see no reason not to follow their advice, unless you are running in extreme conditions (Fairbanks in winter, or Phoenix in summer).
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