Oil, SAE, and what does 10w30 mean, anyway?

[itsid]

SAE seems still confusing to most people...

The "winter" denomination (and yes, W means winter)
is pretty straight forward and easy to remember (for all but americans tbh...)

0°C (freezing water for you fahrenheit users)

Here's how:
20W oil is just liquid enough to be pumped at -20°C (SAE J 300)
and now follow the steps in opposite direction...
15W oil -> -25°C
10W oil -> -30°C
5W oil -> -35°C
0W oil -> -40°C
and of course :
25W -> -15°C
30W -> -10°C etc...

the high temp scale works differently..
it denotes the viscosity of an oil at a fixed (high'ish) temperature namely 100°C (boiling water)
in terms of flow rate
thinnest:
SAE 8 is 1,7 mm²/s
SAE 12 is 2,0 mm²/s
SAE 16 is 5,6 mm²/s
SAE 20 is 6,9 mm²/s
SAE 30 is 9,3 mm²/s
SAE 40 is 12,5 mm²/s
SAE 50 is 16,3 mm²/s
thickest oil
SAE 60 with 21,9 mm²/s

you can take the winter rating as an indicator of ambient temperature.
you cannot do the same with the "summer" rating.. it's pointless...
a combustion engine running is ALWAYS way hotter than the ambient temperature,
so there wouldn't be any point.

but a SAE 30 rating (right part of the number) has always the same min rating (9.3 mm²/s)
no matter what the left side of the number denotes..
it can be better (thicker) but never worse.

so if the manual calls for 10W-30 and you get 5W-30 you will be fine, there will be next to no difference in summer and it only stays liquid enough to start your engine when you left it outside in the winter... in siberia!

'sid

 

[OzFab]

A friend of mine mistakenly filled his engine with 5W-30 oil one winter & wondered why the engine would knock & tap for longer than usual. I suggested he drop the oil & replace it with 10W-30, which fixed the issue...

Can you explain why?

 

[anickode]

A friend of mine mistakenly filled his engine with 5W-30 oil one winter & wondered why the engine would knock & tap for longer than usual. I suggested he drop the oil & replace it with 10W-30, which fixed the issue...

Can you explain why?

Because the engine was spec'd for the 10w30.

Engines are designed for particular oil viscosities for a reason. The reasons can range from pump design to machining tolerances to fuel economy. The difference between a 5w and a 10w on cold startups is significant enough that the manufacturer specified one over the other. If it didn't matter, using the wrong oil wouldn't void your warranty.

 

[Whitetrashrocker]

A friend of mine mistakenly filled his engine with 5W-30 oil one winter & wondered why the engine would knock & tap for longer than usual. I suggested he drop the oil & replace it with 10W-30, which fixed the issue...

Can you explain why?

Cause it acted like this 5 weight when it was cold. The 10w acted thicker and there for didn't knock in the valve train.

 

[Hellion]

Post supplemented for us oddball Fahrenheit users.

Plus, it just sounds cooler to say.

And, if everyone were the same the world would be boring.

SAE seems still confusing to most people...

The "winter" denomination (and yes, W means winter)
is pretty straight forward and easy to remember (for all but americans tbh...)

0°C / 32° F (freezing water for you fahrenheit users)

Here's how:
20W oil is just liquid enough to be pumped at -20°C /-4° F (SAE J 300)
and now follow the steps in opposite direction...
15W oil -> -25°C /-13° F
10W oil -> -30°C /-22° F
5W oil -> -35°C /-31° F
0W oil -> -40°C /-40° F
and of course :
25W -> -15°C / 5° F
30W -> -10°C / 14° F
etc...

The high temp scale works differently..
it denotes the viscosity of an oil at a fixed (high'ish) temperature namely 100°C / 212° F (boiling water)
in terms of flow rate
thinnest:
SAE 16 is 5,6 mm²/s
SAE 20 is 6,9 mm²/s
SAE 30 is 9,3 mm²/s
SAE 40 is 12,5 mm²/s
SAE 50 is 16,3 mm²/s
thickest oil
SAE 60 with 21,9 mm²/s
...



'sid

 

[itsid]

A friend of mine mistakenly filled his engine with 5W-30 oil one winter & wondered why the engine would knock & tap for longer than usual. I suggested he drop the oil & replace it with 10W-30, which fixed the issue...

Can you explain why?

well there are many differences in oils (even if same SAE j300 rated oils) that's why you can find which oils to use even in simple industrial engine manuals.
Like Honda calls for SJ or SL for the GX200
Lifan likes SE or SF for the GX200 clone
both recommend 10W-30 for "ordinary ambient temperatures"..

Frankly, I'm far from being an expert on viscosity or service ratings for oil..
as I said elsewhere.. fluid dynamics (and thus partly viscosity) is not exactly my strong point in physics

I remember one or two things and with a bit of luck where to find more details when needed
(Like I had to look up the viscosity ratings for high temps for example)

but in the end it all comes down to this:

Because the engine was spec'd for the 10w30.

Engines are designed for particular oil viscosities for a reason. The reasons can range from pump design to machining tolerances to fuel economy. The difference between a 5w and a 10w on cold startups is significant enough that the manufacturer specified one over the other. If it didn't matter, using the wrong oil wouldn't void your warranty.

While one pump might be able to pump a certain viscosity at -35°C
another one might fail at doing so at just -10°C already.
what pump (and overall engine design) can deal with what oil at what temperatures is very much a matter of fluid dynamics.
So apart from the manufacturers themselves I doubt anyone can tell really (at best make an educated guess)

Post corrected for us oddball Fahrenheit users.

Plus, it just sounds cooler to say.

And, if everyone were the same the world would be boring.

thanks for adding Fs to my Cs (*giggle*)
but corrected you have not, added to you have. (...young padawan)

but as you can see (which is an essential flaw of stupid Fahrenheits)
it doesn't scale as nicely if you divide the exact same 100s scale (celsius scale which the fahrenheit scale is defined by) into 180 parts and add 32 all the time...
it's what?? cooler?? I beg to differe!
(that's like saying a Aquaman is cooler than Flash )
If you need another system to define "yours" .. yours is obsolete IMHO.
long live the decimal system...
Nevermind, please proceed!

'sid

 

[Hellion]

TL/DR, sorry.

Look at it this way, verbosity is one of your charms, 'sid!

I did correct your grammar mistakes before I snipped it all for brevity.

 

[WeddingRing]

But 'sid, how can you say ambient air temperature doesn't matter with air cooled engines?

 

[Bbqjoe]

TL/DR, sorry.

Look at it this way, verbosity is one of your charms, 'sid!

I did correct your grammar mistakes before I snipped it all for brevity.

I'd say it's more like verbesity!

 

[bob58o]

SAE seems still confusing to most people...

the high temp scale works differently..
it denotes the viscosity of an oil at a fixed (high'ish) temperature namely 100°C (boiling water)
in terms of flow rate
thinnest:
SAE 16 is 5,6 mm²/s
SAE 20 is 6,9 mm²/s
SAE 30 is 9,3 mm²/s
SAE 40 is 12,5 mm²/s
SAE 50 is 16,3 mm²/s
thickest oil
SAE 60 with 21,9 mm²/s

So square mm per second as a flow rate??? I'm guessing it describes how fast the oil spreads. Like at t=0 the oil covers 1 sq mm, and at t=1 sec it covers 2 square mm, ....

The higher the number, the higher the viscosity right? The higher the viscosity, the more opposed to flow it is right?

So why does the thickest oil (60 Weight), which has the highest viscosity, also have the fastest flow rate (21.9 mm^2 / second)??? It would seem thicker, more viscous, liquid would flow slower than a thinner, less viscous, liquid.

Unless I am backwards, I still don't understand.

 

[itsid]

So square mm per second as a flow rate??? I'm guessing it describes how fast the oil spreads. Like at t=0 the oil covers 1 sq mm, and at t=1 sec it covers 2 square mm, ....

The higher the number, the higher the viscosity right? The higher the viscosity, the more opposed to flow it is right?

So why does the thickest oil (60 Weight), which has the highest viscosity, also have the fastest flow rate (21.9 mm^2 / second)??? It would seem thicker, more viscous, liquid would flow slower than a thinner, less viscous, liquid.

Unless I am backwards, I still don't understand.

No worries, I doubt anyone really understands just from the SI units
(unless he's professionally dealing with this kind of stuff and even then it's counterintuitive)

It's not flow rate (which it appears to be)
it's kinematic viscosity (viscosity-density-ratio)

without going into too much details..
it's the amount of shear stress a 100°C oil film can take
trapped between plates one moving at constant speed
the faster the plate can move without breaking the film, the higher the number.
that (dynamic viscosity [kg/(m·s)]) divided by the density [kg/m³] of the fluid. and you end up with m²/s which indeed can be read as "area covered over time"
it's still not the flow rate.

and in case you wonder where the kg/(m·s) in dynamic viscosity comes from
it's a Pascal second (force over area times time)
(Or maybe more comprehensive for our task here: force over volume per speed (N/m³)/(m/s))
(N/m²)·s or (N·s)/m2 with N being (kg·m)/s² you can write it as kg/(m·s).
fancy, isn't it?

'sid

 

[Bbqjoe]

I hate math.
The only thing I like about math is zeros.
Lots and lots of zeros placed behind any number greater than zero.

By the way, ask Seri sometime what zero divided by zero is.

 

[bob58o]

I hate math.
The only thing I like about math is zeros.
Lots and lots of zeros placed behind any number greater than zero.

By the way, ask Seri sometime what zero divided by zero is.

I don't need cookies or friends.

 

[Bbqjoe]

I don't need cookies or friends.

 

[Goat]

SAE seems still confusing to most people...

The "winter" denomination (and yes, W means winter)
is pretty straight forward and easy to remember (for all but americans tbh...)

0°C (freezing water for you fahrenheit users)

Here's how:
20W oil is just liquid enough to be pumped at -20°C (SAE J 300)
and now follow the steps in opposite direction...
15W oil -> -25°C
10W oil -> -30°C
5W oil -> -35°C
0W oil -> -40°C
and of course :
25W -> -15°C
30W -> -10°C etc...

the high temp scale works differently..
it denotes the viscosity of an oil at a fixed (high'ish) temperature namely 100°C (boiling water)
in terms of flow rate
thinnest:
SAE 16 is 5,6 mm²/s
SAE 20 is 6,9 mm²/s
SAE 30 is 9,3 mm²/s
SAE 40 is 12,5 mm²/s
SAE 50 is 16,3 mm²/s
thickest oil
SAE 60 with 21,9 mm²/s

you can take the winter rating as an indicator of ambient temperature.
you cannot do the same with the "summer" rating.. it's pointless...
a combustion engine running is ALWAYS way hotter than the ambient temperature,
so there wouldn't be any point.

but a SAE 30 rating (right part of the number) has always the same min rating (9.3 mm²/s)
no matter what the left side of the number denotes..
it can be better (thicker) but never worse.

so if the manual calls for 10W-30 and you get 5W-30 you will be fine, there will be next to no difference in summer and it only stays liquid enough to start your engine when you left it outside in the winter... in siberia!

'sid

I think fully synthetic oil changes the equation, the flow rate, and temperature range.

 

[bob58o]

I think that if you have cookies, you will have friends. But then your friends will eat your cookies. Then you will have no more cookies. And your friends will leave.

Cookies and Friendships are both exercises in futility.

 

[ezcome-ezgo]

This thread is epic, Sid GAB on fluid dynamics? Bob sitting there just grinning from ear to ear.

A quality of oil which is paramount in it's ability to lubricate is it's ability to stick to metal.

 

[Goat]

This thread is epic, Sid GAB on fluid dynamics? Bob sitting there just grinning from ear to ear.

A quality of oil which is paramount in it's ability to lubricate is it's ability to stick to metal.

What? I thought lubricant was not supposed to stick to metal. That would make it glue like. I am sure I misunderstood.

---------- Post added at 04:43 PM ---------- Previous post was at 04:40 PM ----------

I think that if you have cookies, you will have friends. But then your friends will eat your cookies. Then you will have no more cookies. And your friends will leave.

Cookies and Friendships are both exercises in futility.

Astute. Bob you are wise beyond your years.

 

[itsid]

I think fully synthetic oil changes the equation, the flow rate, and temperature range.

...and you think wrong

'sid

 

[Goat]

I respectfully disagree.