Brain fade re oil viscosity

[Scarletpimpofnel]

I'm struggling to understand oil viscosity. Take say 5w/30.

At -17C approx. the viscosity is 5. At 100C the viscosity is 30.

But surely as you heat oil it becomes LESS viscous not more viscous??? If the numbers were like say 30W/5 then it'd make sense to me. What am I missing?

[Caddyshack]

Scarletpimpofnel said:

I'm struggling to understand oil viscosity. Take say 5w/30.

At -17C approx. the viscosity is 5. At 100C the viscosity is 30.

But surely as you heat oil it becomes LESS viscous not more viscous??? If the numbers were like say 30W/5 then it'd make sense to me. What am I missing?

The numbers mean flow, not thickness, therefore 30 is higher,…..more flow than the cold 5w.

[blueST]

My understanding in layman’s terms is it’s saying it has the viscosity that an SAE 5 oil would have at the cold temp and what an SAE 30 oil would have at the hot the temp.

[Super Sonic]

It resists the thinning effect of being heated, so at a low temperature it has the equivalent viscosity of a thin oil, and at a higher temperature, it has the equivalent viscosity of a thicker monograde oil that has thinned with temperature.

[samoht]

Super Sonic said:

It resists the thinning effect of being heated, so at a low temperature it has the equivalent viscosity of a thin oil, and at a higher temperature, it has the equivalent viscosity of a thicker monograde oil that has thinned with temperature.

This.

It makes more sense if you think in terms of what people used to do before multigrade oils. In those day you might fill with a 5 weight oil in October for the winter, and change that to a 30 weight oil in March for the summer season. Ie actually put in a thinner oil in winter to lubricate better in cold weather.

The multigrade oil offers a single oil which can work year-round, so is advertised as "5w/30" meaning it is like a 5 weight oil in winter but a 30 weight oil in summer, saving you changing the oil twice a year.

[Scarletpimpofnel]

samoht said:

Super Sonic said:

It resists the thinning effect of being heated, so at a low temperature it has the equivalent viscosity of a thin oil, and at a higher temperature, it has the equivalent viscosity of a thicker monograde oil that has thinned with temperature.

This.

It makes more sense if you think in terms of what people used to do before multigrade oils. In those day you might fill with a 5 weight oil in October for the winter, and change that to a 30 weight oil in March for the summer season. Ie actually put in a thinner oil in winter to lubricate better in cold weather.

The multigrade oil offers a single oil which can work year-round, so is advertised as "5w/30" meaning it is like a 5 weight oil in winter but a 30 weight oil in summer, saving you changing the oil twice a year.

"Ie actually put in a thinner oil in winter to lubricate better in cold weather." - This is what I am not getting. How can a multigrade oil be thinner (5) in winter and thicker in summer (30)? Oil surely thins (gets less viscous) in summer? How does oil get thinner in winter?

Everything I read says the 5W/30 mubers are the viscosity so how is the viscosity lower in winter than in summer? CaddyShack above said the numbers mean flow not viscosity. Now flow would make sense to me as I'd expect the flow to be lower in winter (5) than in summer (30).

So is CaddyShack right that actually the numbers mean flow? So why call it viscosity? Appreciate I am being dense here as it is obvious to everyone else!

[Super Sonic]

In winter, a 5 weight oil has the correct viscosity, as the cold thickens it up.
In summer, a 30 weight oil has the correct viscosity, as the heat thins it out.
A 5 wt oil in winter has a similar viscosity to a 30 wt oil in summer.
5w30 resists the effects of temp, so acts like a 5w in winter, and a 30w in summer.

[Caddyshack]

Scarletpimpofnel said:

samoht said:

Super Sonic said:

It resists the thinning effect of being heated, so at a low temperature it has the equivalent viscosity of a thin oil, and at a higher temperature, it has the equivalent viscosity of a thicker monograde oil that has thinned with temperature.

This.

It makes more sense if you think in terms of what people used to do before multigrade oils. In those day you might fill with a 5 weight oil in October for the winter, and change that to a 30 weight oil in March for the summer season. Ie actually put in a thinner oil in winter to lubricate better in cold weather.

The multigrade oil offers a single oil which can work year-round, so is advertised as "5w/30" meaning it is like a 5 weight oil in winter but a 30 weight oil in summer, saving you changing the oil twice a year.

"Ie actually put in a thinner oil in winter to lubricate better in cold weather." - This is what I am not getting. How can a multigrade oil be thinner (5) in winter and thicker in summer (30)? Oil surely thins (gets less viscous) in summer? How does oil get thinner in winter?

Everything I read says the 5W/30 mubers are the viscosity so how is the viscosity lower in winter than in summer? CaddyShack above said the numbers mean flow not viscosity. Now flow would make sense to me as I'd expect the flow to be lower in winter (5) than in summer (30).

So is CaddyShack right that actually the numbers mean flow? So why call it viscosity? Appreciate I am being dense here as it is obvious to everyone else!

I do not think you are being dense at all and I do not think it is as clear as it should be.

I have always thought that if you had 5w50 then you would expect that oil to be much thinner when hot in summer compared to a 5w30. So it could say, "doesn't get too gloopy in winter and won't get too thin when hotter"

[srob]

Caddyshack said:

I do not think you are being dense at all and I do not think it is as clear as it should be.

I have always thought that if you had 5w50 then you would expect that oil to be much thinner when hot in summer compared to a 5w30. So it could say, "doesn't get too gloopy in winter and won't get too thin when hotter"

Isn't the idea that they are a consistent viscosity when warm? The 'multi grade' bit is more to do with when the oil is cold. On our old bikes we run straight oil, and something like straight 40 is nigh on impossible to kick over in winter. So you'd have put in a lighter oil in winter back then so it turns over easier but also I guess so it circulates faster. May be more relevant to air cooled engines?

[Super Sonic]

Caddyshack said:

I do not think you are being dense at all and I do not think it is as clear as it should be.

I have always thought that if you had 5w50 then you would expect that oil to be much thinner when hot in summer compared to a 5w30. So it could say, "doesn't get too gloopy in winter and won't get too thin when hotter"

Wrong. The higher numbers denote higher viscosity. You're just confusing the issue.

[Caddyshack]

Super Sonic said:

Caddyshack said:

I do not think you are being dense at all and I do not think it is as clear as it should be.

I have always thought that if you had 5w50 then you would expect that oil to be much thinner when hot in summer compared to a 5w30. So it could say, "doesn't get too gloopy in winter and won't get too thin when hotter"

Wrong. The higher numbers denote higher viscosity. You're just confusing the issue.

1) Calm down and 2) Edited to add...I got the last bit the wrong way around...50w is thicker than 30w when hot.

[Super Sonic]

Scarletpimpofnel said:

"Ie actually put in a thinner oil in winter to lubricate better in cold weather." - This is what I am not getting. How can a multigrade oil be thinner (5) in winter and thicker in summer (30)? Oil surely thins (gets less viscous) in summer? How does oil get thinner in winter?
[[ It doesn't actually get thinner in winter, it has the viscosity that a thinner oil, thickened up due to cold, would have.
In the summer, it has the viscosity that a thicker oil, thinned by the heat, would have.
In both cases it has the same actual viscosity]]

Everything I read says the 5W/30 mubers are the viscosity so how is the viscosity lower in winter than in summer?
[[It isn't, it has the winter viscosity of a 'thin' oil, thickened by cold,ie medium, and the summer viscosity of a 'thick' oil that has been thinned by the heat, again, medium. So the actual viscosity remains similar.]]
CaddyShack above said the numbers mean flow not viscosity. Now flow would make sense to me as I'd expect the flow to be lower in winter (5) than in summer (30).
[[Caddyshack is wrong, as a quick web search will show. The number is viscosity.]]

So is CaddyShack right that actually the numbers mean flow? So why call it viscosity? Appreciate I am being dense here as it is obvious to everyone else!
[[Caddyshack is just confusing you!]]

[Super Sonic]

Caddyshack said:

1) Calm down and 2) Edited to add...I got the last bit the wrong way around...50w is thicker than 30w when hot.

I'm calm.
In your first post you said the numbers mean 'flow', and that a higher w oil flows better than a lower one. In your second you said, after editing, the higher numbers are thicker. It can't be both. You're just confusing the issue

Edited by Super Sonic on Wednesday 27th March 15:52

[Caddyshack]

Super Sonic said:

Caddyshack said:

1) Calm down and 2) Edited to add...I got the last bit the wrong way around...50w is thicker than 30w when hot.

I'm calm.
In your first post you said the numbers mean 'flow', and that a higher w oil flows better than a lower one. In your second you said, after editing, the higher numbers are thicker. It can't be both. You're just confusing the issue

Edited by Super Sonic on Wednesday 27th March 15:52

Yes, I did an edit to correct it - therefore removing the confusion.

[Super Sonic]

Caddyshack said:

Yes, I did an edit to correct it - therefore removing the confusion.

Your first post contradicts your edit of your second one.
Your first post says higher numbers flow better.
Your edit of your second post says higher numbers are thicker.
Can't be both.

[Caddyshack]

Super Sonic said:

Caddyshack said:

Yes, I did an edit to correct it - therefore removing the confusion.

Your first post contradicts your edit of your second one.
Your first post says higher numbers flow better.
Your edit of your second post says higher numbers are thicker.
Can't be both.

That is why the last post clarified that.

My first post does explain the way to think of it is flow which it does. It is just that the bigger the number on the end means thicker and is the hot reading.

It isn’t a competition.

Edited by Caddyshack on Wednesday 27th March 16:44

[tim1830]

I think you have to remember it's terminolgy, it's weight and flow

https://www.youtube.com/watch?v=V5a4kP-5Jiw

I think oil is the only fluid that thickens when hot? I am probably wrong

[Caddyshack]

tim1830 said:

I think you have to remember it's terminolgy, it's weight and flow

https://www.youtube.com/watch?v=V5a4kP-5Jiw

I think oil is the only fluid that thickens when hot? I am probably wrong

That is an amazing vid, ok -40 is an extreme but I would not have thought it would be that different. Makes you think that we really should pay more attention to those numbers.

[Super Sonic]

Caddyshack said:

The numbers mean flow, not thickness, therefore 30 is higher,…..more flow than the cold 5w.

Contradicted by the video.
I'm aware it's not a competition, it's just with you claiming two contradictory things, I wasn't sure what you were trying to say.
Your edited post is correct.

[Super Sonic]

tim1830 said:

I think you have to remember it's terminolgy, it's weight and flow

https://www.youtube.com/watch?v=V5a4kP-5Jiw

I think oil is the only fluid that thickens when hot? I am probably wrong

You're definitely wrong.