[jbollis]

Originally Posted by cubs-n-bxrs

Your whole theory is backwards. This was taken off of the Amsoil website.
OK . . .What does a 5W-30 do that an SAE 30 won't?
When you see a W on a viscosity rating it means that this oil viscosity has been tested at a Colder temperature. The numbers without the W are all tested at 210° F or 100° C which is considered an approximation of engine operating temperature. In other words, a SAE 30 motor oil is the same viscosity as a 10w-30 or 5W-30 at 210° (100° C). The difference is when the viscosity is tested at a much colder temperature. For example, a 5W-30 motor oil performs like a SAE 5 motor oil would perform at the cold temperature specified, but still has the SAE 30 viscosity at 210° F (100° C) which is engine operating temperature. This allows the engine to get quick oil flow when it is started cold verses dry running until lubricant either warms up sufficiently or is finally forced through the engine oil system. The advantages of a low W viscosity number is obvious. The quicker the oil flows cold, the less dry running. Less dry running means much less engine wear.

I have to agree with you on that.
Harley recommends there own 20w-50 for for there v-twins. I can guarantee anyone that the engine in my Harley runs way hotter then any of our tractors do. It is 95 ci, 10.9:1 compression, runs on pump gas, makes 117 hp / 121 lb-ft torque at the wheel, and has been doing it for 11 years now. My oil temps run anywhere between 210* and 250*. Have seen it as high as 265*.