The people that built the bike have taken all of that into consideration and provided all of us with the data...it's in the owners manual in the recommended oil section.

W40 provides the same performance as W50....WHEN the outside temp is 40 degrees or less...I know this because the Harley engineers tell me to run a W40 oil in sub 40 temps. So, I am trusting, they've ran the tests.

For my bike, I can run, W60, W50 or W40 oil; which one depends on air temps.

Idiot proofing instructions is important, when the average idiot is standing in the Walmart oil section, they easily find 10W40 and 20W50 motorcycle oil! So listing those two oils in the manual gives 99.9% idiot proofed oil selection...and for 100% idiot proofing of Harley riders, they tell us to put the same oil in all three holes Yeah, that's what they think of us Harley riders "abilities"..

So, if we stop there, the majority are good to go.

But for people that enjoy the subject, it's much deeper.

The truth is, if you have wide swings in air temp, the number before the W should be as low as you can go as long as the number after the W is correct for expected ambient air temps.

So, for sub 40 temps, the manual says 10W40; but that's just to keep it simple...the more complicated truth is that the 0W40 is a better choice than 10W40 as you will get faster initial lubrication at startup and better flow while the engine warms; while still giving you W40 at ~200F as the engineers want. But, the negative of a wide gap between the W is shear..the harder and farther you run the oil, the closer it will get to left number of the W when the engine is HOT...so if you run a 0W40 oil 10,000 miles....you've probably got 0W5 oil running in that hot engine...a replace engine soon scenario.

Now, imagine if all this was in the owners manual; heads would explode...so it just says, "use 20W50 for most situations" and at Wallyworld, right there on the shelf, whata-you-know..20W50 motorcycle oil.

 

Not everyone is an oil genius like you.

Things that make peoples head explode:

Your long winded posts of rehashed general internet oil information.

 

It's funny how everyone has a fact based opinion that tends to be biased. One thing I do know is the fact that most wear and tear to a motor is at cold startup. The other thing I do know is that some oils perform better than others at specified high temps. With that in mind what could possibly be wrong with a 0 or 5w cold start motor oil...? I can understand the relation to heat and viscosity, But what about the improvement of Dino to Synthetic. Most synthetics protect better than Dino. So if I went from a better cold starting oil and also from a Dino to a Synthetic (that gives better protection) What what is the real issue? How am I not gonna have the same or better protection? When I was involved with modifieds (dirt track cars) we tried to keep the oil temp between 165-180* (in the sump) it offered the best protection without thinning the oil too much.... The other thing I was curious about was that , yes I know the thicker oils will maintain better oil pressure but in our Air cooled ball/tapered bearing motors where's the resistance to build pressure? unlike an automobile motor with Clevite 77 bearings set to .0025" clearance our V-twins rely on volume not pressure so how do you increase volume? The only 2 ways I know is a high volume oil pump or an oil that will flow better at higher temps without sacrificing protection....

So here's my deal I have an oil cooler and when using Dino oil, my oil temps in the tank (softail) usually run right at 165* with cold oil pressure @45 psi and hot @22-24psi (I upgraded the spring in the stock Evo pump). Since then I purchased and installed an S&S HVHP pump. So if I increased the volume and keep the temps down and went from a Dino to a synthetic, what am I doing wrong? Where is the real harm to the motor?

 

I am not understanding this. Are you saying that 20w-50 will flow like 20 at 100 degrees but flow like 50 at 200 degrees?


So, if I warm up my engine by putting 30 miles on it before I drain my oil. It is going to come out the drain plug at a viscosity of 50, but when I pour the fresh oil in. It is going to pour at a lower viscosity?

 

Don't know where the 100*,200* rating came from but this should sum it up nicely as taken from a Popular Mechanics article from this link...

https://www.google.com/amp/www.popul...o/a53/1266801/

Viscosity

Viscosity (a fluid's resistance to flow) is rated at 0° F (represented by the number preceding the "W" [for Winter]) and at 212° F (represented by the second number in the viscosity designation). So 10W-30 oil has less viscosity when cold and hot than does 20W-50. Motor oil thins as it heats and thickens as it cools. So, with the right additives to help it resist thinning too much, an oil can be rated for one viscosity when cold, another when hot. The more resistant it is to thinning, the higher the second number (10W-40 versus 10W-30, for example) and that's good. Within reason, thicker oil generally seals better and maintains a better film of lubrication between moving parts.

 

OMG, there is so much misinformation here....

First off, there is no such viscosity as w40, w50, w60 or w anything.

The "w" is carried with the number preceding the w and the w means "winter"

The numbers to the right of the "w" are just SAE 40,SAE 50, SAE 60 IF THEY ARE STRAIGHT WEIGHT. Some times they are designated as 40w, 50w, 60w.
In this case the "w" is weight.

As far as first number at 100 degrees and second number at 200 degrees..not true.

The first number, 20w is at 0F and the second, 50 is at 210F (100C).

Hope this helps.

Ken

 

20w50

20w50 oil at 0 degrees and SAE 20 at 0 degrees will have the same viscosity.

20w50 oil at 210 degrees and SAE 50 at 210 degrees will have the same viscosity.

They taught me this in Airframe and Powerplant school (40 years ago ).

 

Y22C, 98 is correct the W stands for "Winter" not weight. This has always confused many a persons for may a year.

 

20w50 oil at 0 degrees and SAE 20 at 0 degrees will have the same viscosity.

Wrong, a 20W50 and a 20W will meet the same viscosity specs at 0F

20w50 oil at 210 degrees and SAE 50 at 210 degrees will meet the same viscosity specs.

Correct.


There is a BIG difference between a 20w and a SAE20

Ken

 

Sorry for restating.

Ken