Oil viscosity - I'm confused | GTAMotorcycle.com

Oil viscosity - I'm confused

jeero

jeero

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Been reading a few different websites that basically say the same thing but it doesn't make sense in my head.

They all say that the higher the number on the viscosity rating, the thinner the oil.
This I agree with because when I pour in new oil it has some kind of thickness to it kinda like honey but not as thick, and when I do an oil change 20 minutes after riding the bike it comes out like water (very thin).

So, a common oil like 10W30 for example.
According to what I've read, the W means "Winter" and not weight as some people believe. This is to indicate that it is a multigrade oil and uses polymers to change viscosity as the temperatures go up.
The second number in the rating is the viscosity at 100 degrees Celcius which is considered operating temperature for most vehicles.
So far I still understand. When you start the car/bike the oil has a viscosity rating of 10 and as the temperature rises, it thins out and behaves like a 30.

Now where they confuse me:
They (websites I looked at) said a 5W30 is thinner than a 10W30 and is preferred for colder temperature starts.
What happened to "the higher the number, the thinner it is?"

And also, that statement still doesn't make sense to me because I put 90 weight gear oil on my chain and it's thicker than honey, has to be applied with a brush.


If anyone can chime in and set me straight, it would be very appreciated.
Worry not, I put the recommended oil according to the manual of my bike. I just want to make sense of all these contradicting statements I have been reading (while bored at work).


Thanks
 
jeero said:
They all say that the higher the number on the viscosity rating, the thinner the oil.
Click to expand...

Name one place where you've seen that stated - because it's wrong.

Re the oil change 20 minutes after running the bike ... The absolute viscosity of ANY oil is strongly temperature dependent. 20 minutes after running the engine, it is still well above ambient temperature, and that is why oil drained out in that manner is thinner than when you put it in.

"So far I still understand. When you start the car/bike the oil has a viscosity rating of 10 and as the temperature rises, it thins out and behaves like a 30." Correct.

"They (websites I looked at) said a 5W30 is thinner than a 10W30 and is preferred for colder temperature starts." Correct.

You are being confused by thinking that the bigger the number, the thinner it is, because that's flat out wrong, and I'd like to see where you got that impression.
 
So perhaps that's where the confusion is coming from?
Multigrade oils get thicker as the temperature reaches 100C?

I'll try to remember to get the links I visited and edit them into this post.
 
Read this http://www.upmpg.com/tech_articles/motoroil_viscosity/

Basically a 10W30 oil has the viscosity of a 30 Weight single grade oil at 210 deg F or 100 deg C normal car operating engine temps. Where the 10 in 10W30 comes to play is that with additives when the oil is cold it has the viscosity of a 10 Weight oil so that in cold temps the oil still flows well at engine start up so that you can start the engine and also have oil that flows enough to lubricate the engine. If you used a single weight like 30W in cold weather the oil would be thick as molasses and you would have a hard time cranking over the engine and because it is so thick would not pump through the engine very well until the engine warmed up causing wear.

The colder it is using a 5w30 or 0w30 flows better when cold.

Most air cooled bikes use 10W40 (40 weight that flows like a 10 weight when cold) because the engine temps are higher needing an oil that does not get too thin as engine temps get hotter.
 
Just to confuse you further; Viscosity is NOT a measure of "thickness" of a liquid, but a measure of how well a liquid adheres to stuff.
A good quality Quebec maple syrup, which pours like water, has a higher viscosity than axle grease, which is a paste.
 
jeero said:
So perhaps that's where the confusion is coming from?
Multigrade oils get thicker as the temperature reaches 100C?

I'll try to remember to get the links I visited and edit them into this post.
Click to expand...

Its the additives that are messing you up. Multigrade oil has additives for winter weather so the oil doesn't become solid. So your 10w30 with flow like SAE 10 Oil at low temperatures. But when heated will act like a SAE 30.

Try looking at this site. http://www.upmpg.com/tech_articles/motoroil_viscosity/

Edit: Damn! The Taximan beat me too it!
 
bitzz said:
Just to confuse you further; Viscosity is NOT a measure of "thickness" of a liquid, but a measure of how well a liquid adheres to stuff.
A good quality Quebec maple syrup, which pours like water, has a higher viscosity than axle grease, which is a paste.
Click to expand...

I think you broke my head... I hate you now :)

And I'm also wondering if i can run my motorcycle on maple syrup lol
 
Last edited:
First of all, thank you for the information and explaining it in a way that (I think) I understand.
Let's see if I get this right now:

So the lower the number, the lighter it is, which makes it flow better (such as cold weather starts), which explains a 5W or even 0W for climates that are always brisk in the winter.

Using an oil that is much lighter than recommended (at operating temperature) won't "stick" to the components enough to lubricate them as they need. Let's say my car wants a 40weight but I put in some 5W15 instead, I could be shortening my engine's life.


Did I pass the quiz? :D




bitzz said:
A good quality Quebec maple syrup, which pours like water, ...
Click to expand...

Being from Québec, all I can say is Amen brother!
 
bitzz said:
Just to confuse you further; Viscosity is NOT a measure of "thickness" of a liquid, but a measure of how well a liquid adheres to stuff.
A good quality Quebec maple syrup, which pours like water, has a higher viscosity than axle grease, which is a paste.
Click to expand...

That's not true at all.
Viscosity is a measure of a fluid's resistance to flow.

Viscosity is not a measure of how well a liquid adheres to stuff.

This may help you understand -- http://www.research-equipment.com/viscosity%20chart.html
 
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