Ok, I am sure that this has been beaten to death on here, but I can't seem to find the answers that I am looking for using the search function.

I have been using Mobil 1 20W 50 for several years now, and am getting really tired of paying $10.50 per quart. Walmart has Mobil 1 15W 50 in 5 quart jugs for $22.50. I know that a lot of guys are running this stuff, and from the research I have done so far, there is no harm in it.

As far as I can tell, the high (operating) temperature viscosity of 15W-50, 20W-50, or even SAE-50 are all the same. As I understand it, 15W and 20W are nothing more than a measurement of the viscosity of these oils at low (resting) temperature. The first number with a (W) is the rate at which the oil will flow through a viscometer when it is cold. The higher the number, the slower your cold engine gets lubricated. 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.

Assuming that is all correct, its seems to be a no brainer changing over to 15W-50. If this is the case, then why are most all motorcycle oils 20W and not 15W? There must be a reason. What is the benefit to 20W?

 

I think that the "benefit" of a synthetic "motorcycle" oil rated 20w50 is so that it will "match" up with the motor companies recommended viscosity of 20w50. I've read that a real synthetic 20w50 "motorcycle" oil actually qualifies as a 15w50 but the oil companies just label it as a 20w50 so the average person will more readily recognize and accept it for their motorcycle. If I were you, I'd use the 15w50 without hesitation if that is the brand that you like. "Motorcycle" labeled oils are mostly marketing. Check out the specs for whatever oil your interested in and look for others who may have used it and had used oil analysis done or had extensive experience using it. BITOG (bob is the oil guy) is a good source for oil information.

When it's all said and done, for all the research that I've done, I believe that just the fact that regular changes (2,500 to 5,000 miles) are done using any modern appropriate viscosity oil for the expected ambient temperature is the most important factor in providing proper protection.

In my '97 RoadKing I've used HD, RevTech, Amsoil, Rotella, and right now, it's got Havoline...all have worked with no discernible difference. I run the "dino" oils around 2500 miles, while I did let the Amsoil go 5000 miles (or one year) ... but return on investment says that "dino" is the best bang for my buck at my present yearly mileage.

 

I understand that 15w or 10w are more susceptable to shearing.

 

Sorry for my ignorance, but what is shearing? If what you are saying is true, it must only be an issue during start/warm up.

 

http://www.bobistheoilguy.com/oilshear.htm

 

The 15w50 will shear to a 40w in about 1000 miles in a HD engine based on UOA tests. But Advanced Auto has Vtwin 20w50 on sale for $7.99 right now.

 

It is an issue where the oil molecules actually get ripped apart by the mechanical contact forces in your engine. The most shear resistant oils are straight weights.

 

Usually true in multi-grade oils the larger the spread between the 2 numbers would be the oils that shear most. Ex. 10w50 would shear more than 20w50 etc.

 

By what I've read, just about any of the 20w50s (including H-D's) will shear to 40 grade and then stay there whereas a HDEO 15w40 will pretty much stay in grade ... so, I take the slight shearing as a non issue ???

 

There is quite a bit of information on this exact comparison on this forum, with some very knowledgeable responses and experiences. I have no issue with the 15W-50. For me an oil change is cheap insurance, and I change oil and filter every 3,000. For me that seems to work out to about two changes a year, with the second falling at the end of riding season, so she gets garaged with new fluids. I see no difference in top end noise or oil pressure, and Mobil 1 is a lot easier to find than some of the synthetic 20W-50 oils. By the way....it seems Wal-Mart has dropped the five gallon jugs of 15W-50 Mobil 1.

Thanks,
bomtek44