Viscosity chart explanation

[cven]

http://www.tlzone.net/forums/tl1000s-tl1000r-forum/110779-synthetic-blend-2.html

Can someone explain the oil chart that is posted in the link, it is cornfusing me!?! Why does it show a straight 50 as a 50 weight at 0 deg? I thought a 50 weight was a 50 weight at 100 deg C?


I'm learning as I go and need some help understanding the "W" rating of oil.

From what I understand a 5w30 oil is the viscosity of a 30 weight at 100 deg C. Now the 5 part is NOT a viscosity at all but a number based on "low temp properties" that has nothing to do with viscosity, am I correct on this?

Thanks for any help.

 

[Quattro Pete]

That chart seems messed up (at least the Y axis). As you said, the numbers after the "w-" describe viscosity ranges at 100 deg. C. What it should have on the Y axis is the actual kinematic viscosity, not SAE grades.

He's basically trying to show that the viscosity of an oil goes down as the temperature goes up, but the rate at which it goes down varies depending on the oil grade. However, the way he set this chart up seems strange.

 

[Scimmia]

yeah, that chart is pretty misleading.

You're right, a 50 weight oil has to be a 50 weight at 100C. The W number does refer to the viscosity, but at very low temps. A 5W oil has to be at better than 6600 cP at -30C

 

[XS650]

Originally Posted By: cven

I'm learning as I go and need some help understanding the "W" rating of oil.

From what I understand a 5w30 oil is the viscosity of a 30 weight at 100 deg C. Now the 5 part is NOT a viscosity at all but a number based on "low temp properties" that has nothing to do with viscosity, am I correct on this?


The 50 number isn't a viscosity either. It's a number that SAE J300 uses to represent a range of actual viscosities at 100C.

Instead of 50, SAE could have just as well used "C" or "Aardvark" in SAE J300.

The TL post adds to the confusion by claiming that the xW rating has something to do with Viscosity at 0F. It did at one time but hasn't for over 40 years now. the xW number does represent a range of viscosities, just as much as the 50 does, only the xW is rated at various temperatures below 0F, some well below 0F.

 

[Quattro Pete]

Originally Posted By: XS650
Instead of 50, SAE could have just as well used "C" or "Aardvark" in SAE J300.

Mobil 1 20w-Aardvark. Now that would be cool.

 

[Gary Allan]

The chart would make more sense if he used Cst at the given temp. The basic concept being communicated is that multi-viscosity oils resemble lighter fluids at colder temps ...where they are very heavy/thick ..but not as thick as a straight grade of the same designation/grade at the same lower temperature.

 

[cven]

Thanks for the replies.

I guess that chart is not made to scale and is for general purpose explanation? It messed me up right from the get go having the 50wt shown as a 50wt at 0* C. (Still don't quite get that)

I understand 50wt represents a range of viscosity at 100* C (nothing else), the thing I was asking is the 20w part is not based on viscosity but based instead on the "low temp properties" the oil has on different tests... cold cranking... ECT.....?



And who gave you my idea for Aardvark oil??? I'm going to use it like the turtle wax logo! It has "Special Stuff" that forms a shield over metal parts cutting wear 50% of 50% of 50%!! LOL....

 

[Gary Allan]

Quote:
I understand 50wt represents a range of viscosity at 100* C (nothing else)


No. SAE 50 represents a grade of oil that falls between 16.3-21.89 Cst @ 100C.

It will still be SAE 50 at any temp, but it will not be 16.3-21.89 Cst.

One could say that it would be equivalent to a much heavier oil at lower temps ..but it's still what SAE 50 appears like at that temp.


Multivisc fluid react like lighter fluids in extreme cold ..and resemble heavier fluid at 100C. They "simulate", through manipulation, lighter or heavier oils depending on the temp. They're always thicker when cold. They either thin less or thicken less than they normally would at opposite ends of the temp scale.

 

[cven]

Thanks again. Yes, 50 wt= 16.3-21.89 Cst at 100* (nothing else from what I understand) I didn't give the "range of viscosity" at 100* C ,couldn't remember it off the top of my head.

Running some thinnish 40wt (13.5 Cst, IIRC) Brad Penn Motorcycle in my bike right now.

the thing I was asking is the 20w part is not based on viscosity but based instead on the "low temp properties" the oil has on different tests... cold cranking... ECT.....?

My reason for the question is IIRC BITOG's own viscosity chart says W rated oils are rated on "low temp properties" not "low temp viscosity"

 

[Gary Allan]

The reason the visc chart reads that way is that there is no such thing as SAE 10 or SAE 5. It is misleading. There can be a designated 10w oil ..that's in the 20 grade range @ 100C ..but doesn't have a HTHS of at least 2.6 ..so can't be called a 10w-20.

https://bobistheoilguy.com/forums/threads/so-what-does-w-mean.9734/

 

[cven]

That is just the kind of info I was looking for, Thanks a bunch!

This line from the thread says what I'd been thinking but I didn't understand it quite right or have any info to explain it.

Yes, the method for determining the number that precedes the W is totally different than the other number. If both numbers were a measurement of kinematic viscosity at 212F for the 2nd number and say, 0F for the fist number, then 10w30 would read more like 400W-30


I don't have much luck using the search function on this board, but I will keep trying.