Wal-Mart has always been a hit or miss deal for me at least the one I go to. I'll grab what I think I need when I see it because it's more than likely I'll never see it again.

To the OP, I'd save the $$ and just go with the 15w-50 and don't worry about it. I buy whatever brand of synthetic I can grab and have yet to succumb to the marketing BS that surrounds these supposed mc specific V-twin oils.

 

Guess I'm the cheapest one here. I run shell rotella 15w40 year around. I put in a couple ounces of STP during the summer. Been doing this for years and never had a oil related failure. With the miles I ride it gives me the best bang for the buck. The MOCO recommends an oil that is rated for diesel engines. Modern automotive oils don't have the extreme pressure lubricants anymore because they are bad for catalytic converters....

 

True, but Mobil1Vtwin is not an automotive oil and neither is Mobil1 15w50 and both contain AW additives. The auto oils you are thinking about are the 5w30 and below with the starburst on the label.

 

The 15/50 will shear a little faster then the 20/50. I have seen it in oil test results. Will it matter? Not a whole lot. Unless you are living in 100+ temps I wouldn't worry about it. Both are good oils and should provide more then enough protection for your motor. Years ago I ran the 15/50 for 32,000 miles. I tore the motor down and was shocked because it looked brand new when I opened it up.

 

I've run the Mobil 1 15W50 for a couple of years with no issues. Even Donnie Petersen recommended the Mobil 1 15W50 in American Iron magazine a couple of years ago.

 

The reason 20w50 is the most common recommendation for motorcycles, is that they are run only in the warmer months. Lighter oil than 20 weight,which is plenty light anyway, is not needed.

 

Old thread, but I wanted to offer some correction for readers. Since I'm reading this thread, other people will too. Don't want any adult men whining that I've revived an old thread.


Oil grade recommendation is, in part, affected by temperature, but generally not until temperature extremes are reached .. ie below 40 degrees or above 100F is when you generally drop or increase grade.
This is what everyone remembers in old owners manuals, several different oils recommended depending on temperature, because all that was available was straight grade or poor performing multi-grade oils.
The truth is oil grade has mostly to do with the engine design, tolerances, and intended use of the engine (engine, load, temperatures, running duration).

Second point, '20w' does not translate to "twenty weight". What it means is WINTER. Essentially, it is the winter number.
The last number is the grade at temperature or 'weight'. In this case, 20w50, which emcompasses a range of oils that can be on the lighter end of specification or on the heavier side of specification.
It is a 50 "weight" because at temperature it meets a certain cSt range of viscosity. When talking synthetics.. the first number is generally not something you should pay too much attention to as synthetics pump very well in cold temperatures and are not subject to the same challenges of older multi-grade oils that used low grade base oils and achieved grade through the use of a polymeric thickening agent.

Bottom line:
Synthetic is good, focus on the last number, and if you really want to know THE MOST important thing that you could ever do pertaining to your oil.. that would be to CHANGE IT OFTEN, even $20/qt special ester blend is superior oil, IN THE REAL WORLD it is better to run the $5/qt Mobil 15w50 and change your oil twice as often. Same thing for your automobiles, run the cheaper synthetic (Walmart Supertech) and change it sooner than you would if buying Mobil 1 because it's better to run similar quality at a cheaper price and change sooner based on years of analysis.

I'm barely scratching the surface.. but if you REALLY want to know the viscosity of an oil, you must become familiar with a unit of measurement called a centi-stoke (metric system like centi-meter).
All lubricants are provided with specifications listed in cSt or centistokes to indicate viscosity of the fluid. You can get oils that are technically on the heavier side, or lighter side.
For example, a light 50 weight is actually very similar to a heavier 40 weight oil.
Going back to the first number.. 20, this number indicates pumpability of the fluid at 0C.
What it means is the fluid "pumps like" a twenty weight oil would pump if it were subjected to freezing temperatures. It doesn't mean it's thin and fast flowing, it means like a 20 weight as if you put a quart of oil in the freezer until it reached 32F. Not trying to write a book so I'll stop before I even begin to touch on any further detail.
This may seem confusing, but that is how it works. Many full-time mechanics don't have a basic understanding of motor oil and lubricants, they just go by a book, so most people do actually get this wrong and commonly call oil like a 20w50 "20 weight". People will think something is wrong running a 5w50 instead of a 20w50 and that's just not so, what it means is that 5w50 uses superior base oils to offer extreme performance characteristics. If a synthetic oil is marketed as 5w50 you can be certain it contains significantly more, if not 100% synthetic base oil molecules. Anyway, just go change your oil no matter how good you think it is.

Now you guys who like diesel oils.. 15w40 Rotella is what I like in the primary because it's moly free and is a perfect chaincase/clutch oil.
Some run it in the engine too, personally however I would only run 40 weight in the engine if it is a synthetic diesel oil such as Rotella 5w40 or Valvoline Premium Blue.
Transmission GL-4 rated synthetic gear oil. You won't find it easily at the store, general rule is do-not ever install a GL-5 rated oil in any component of a motorcycle or car except rear differentials (Rear axle of a truck).

 

or, just follow any owners manual lubricant type and service schedule and not ever have to read or think about anything else..it really is that simple

 

My understanding is most 20W-50 specific motorcycle oils are more of a diesel grade oil with some additives.

They mostly settle out if you let it sit in my opinion.

15W just let's it flow a tad better at a tad lower temperature then 20W. It's a little common sense to rationalize that 15W -50 is 20W and 25W and 30W ECT.. 20W-50 is not 15W however.

The 15W and 20W really only come to play in extreme cold, a weak battery. Real world mean nothing.

I ran MOBILE 1 15W-50 in a aluminum block and head Z28 till at a little over 100K when I lost a head gasket and tore into it. Cylinders and pistons were like new

My Harley has lived on it and now at 50K runs like new. (Sadly eye candy now). But I have been testing different (proper ) grades Mobile 1 since 2005 in 5 new vehicles. Only one does not like is is a Wrangler that I did a inframe overhaul at 300k.

While anything is under warranty, run what owners manual calls out. And keep receipts till it does.

Use non detergent Formula+ in no filter transmission and primary..

 

WTH! Is that even possible?