oil temp vs. viscosity

[wileyE]

Was playing around with an online calculator comparing the difference between a 10w40 and a 20w50 at different temps. On another forum there is concensus that 20w50 is mandatory due to high oil temps(near 300f) a certain machine produces in spite of the factory 10w40 advisory. Here's what I see using the calculator, it appears as temps go up near 300f, there is not much difference between the two grades. I'm just a hacker at this stuff so it's not conclusive of anything, but I found it interesting in light of all the worry about needing thick oil for bikes that run hot. At 300f they are nearly the same, and if the 50w had sheared from being too thick at normal oil temps it's quite possible the two grade would be at least equal.

10w40
13.3@212f
10.3@230f
7.8@250f
6.1@270f
4.2@300f

20w50
17@212f
12.5@230f
9.1@250
6.7@270f
4.4@300f

 

[Titan]

Nice! I THINK I recall the hottest the oil in my air-cooled motorcycle engines reached (measured at the oil fill hole), was just over 250 F. It was in traffic, and it was pinging. I'm sure some internal parts are hotter, of course, but, this makes a good point. Since they aren't really all that much different at operating temps, and most wear happens at start-up, it's another reason that using the thinnest oil for your application is a good idea.

 

[JAG]

Kinematic viscosity is the viscosity at very low shear rate and at atmospheric pressure. It has limited relevence, especially in a shared sump motorcycle. HTHS is viscosity at 302F and certain high shear rate. It still does not fully capture the viscosity-pressure dependence but we can't have it all.

 

[Master ACiD]

i wouldnt worry about the viscosity so much as i would worry about changing the oil often enough in a shared sump bike.
the transmission beat up the oil real good. the clutch is constantly shedding wear particles into the oil. this oil has to lubricate the engine.

in a more refined bike like my boxercup with its independant engine and trans and dry automotive style clutch, i could see messing around with the viscosity and letting the oil change intervals go out alot farther sence the engine oil doesnt deal with transmission abuse or clutch fibers. plus it has a nice sized pair of twin oil coolers to boot.

but in a regular shared engine and trans? no way.

 

[Titan]

Good point. I agree that shared transmission/engine sumps pose a particulate problem, as well as maybe more shearing problems compared to non-shared lubricant compartments. I found I have to run slightly higher viscosity than the engine is spec'd for, in order to get the transmission to behave. BMW and Harley have a better set-up in regard to oil change intervals...but, there are advantages and disadvantages to each setup.

 

[G-MAN]

This calculator works with SUS vis when you input temp in F, so I think your numbers are off.

 

[wileyE]

so wheres the smiley that bangs it head on the wall? back to the drawing board

10w40 20w50

100c 15.9 20.2
230f 12.3 15.1
250f 9.4 11.2
270f 7.2 8.5
300f 5.0 5.6

 

[Norm Olt]

"...in a MORE REFINED BIKE like my boxercup..."

Hahahahaha! That's really a good one!

More "refined" than what, exactly?

Cheers!

 

[wileyE]

Probably more refined than any other aircooled twin still being made? 'cept maybe the ducati? They seem to pull more out of those boxers each year so apparently the evolution hasn't peaked yet. Like Porche, they will make the switch eventually.