The Meaning of W

[Black Bart]

I keep seeing reference to the W as meaning Winter grade on a lot of forums.
I thought the W was referring to the method used for testing.
I'm I correct about that.

 

[flatlandtacoma]

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I'm I correct about that.

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Okay.

 

[Dr_No]

W stands for you are (Wrong)

 

[Pablo]

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I keep seeing reference to the W as meaning Winter grade on a lot of forums.
I thought the W was referring to the method used for testing.
I'm I correct about that.

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Neither are technically correct. Simplistically - W has been said to mean winter and how an oil fits on the 2nd-4th columns on this chart: http://www.infineum.com/information/api-viscosity-2004.html

 

[Merkava_4]

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http://www.infineum.com/information/api-viscosity-2004.html

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Low Temperature (°C) Cranking Viscosity(3), mPa-s Max

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mPa-s =

 

[hominid7]

The "W" means the oil is suitable for winter use. That's why you have 0w, 5w, 10w, 15w, and 20w oils. Oils with higher (thicker) viscosity do not carry the 'w' so those are listed as 30, 40, 50, 60, etc....

I see people write "I use 40W oil in my mower" or something like that all the time, and it is wrong. There is no 40W SAE grade engine oil.

There are thicker gear oils that carry the 'w', such as 70w, 80w gear oil, but those are gear oils, not engine oils.

Multi viscosity oils carry the 'w' in front of the proper winter rated viscosity, such as 10w40, 5w30, 20w50, etc...

 

[TallPaul]

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The "W" means the oil is suitable for winter use.

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Maybe it does, but I never thought of 20w50 as winter oil, unless maybe you live in Atlanta or some place similary down south.

 

[TallPaul]

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mPa-s =

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Note #1 under the chart gives a conversion for this to cP, which is not quite all the way to cSt, but probably could find that conversion on the web. I think I had it figured out once, but have forgotten.

 

[Merkava_4]

This is the way I understand it and you guys can correct me if I'm inaccurate:

10W-30 =

The viscosity of SAE 10 when cold.

The viscosity of SAE 30 when hot.

Motor oils naturally thin out {decrease in viscosity} as they increase in temperature.

A 10W-30 will start out as a 10 weight when cold and then thin down to the viscosity of a 30 weight when hot.

If the 10 weight didn't have viscosity index improvers to {offset/counteract} the effects of thinning out as temperature increases, it would be a very thin 10 weight at 212*F.

 

[dwendt44]

Back in the 50s and 60s, many folks would change to straight 20W for the winter, go back to straight 30 or 10W40 in the summer.(upper mid-west)
5W wasn't available yet.

 

[LargeCarManX2]

The meaning of W.....=Weight!

 

[ThirdeYe]

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This is the way I understand it and you guys can correct me if I'm inaccurate:

10W-30 =

The viscosity of SAE 10 when cold.

The viscosity of SAE 30 when hot.

Motor oils naturally thin out {decrease in viscosity} as they increase in temperature.

A 10W-30 will start out as a 10 weight when cold and then thin down to the viscosity of a 30 weight when hot.

If the 10 weight didn't have viscosity index improvers to {offset/counteract} the effects of thinning out as temperature increases, it would be a very thin 10 weight at 212*F.

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What I never understood about that, is isn't 10<30? I know oil tends to thin as it gets warmer, but shouldn't it be 30w10? Perhaps someone can help me with that, I never understood it.

 

[TallPaul]

.

 

[TallPaul]

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This is the way I understand it and you guys can correct me if I'm inaccurate:

10W-30 =

The viscosity of SAE 10 when cold.

The viscosity of SAE 30 when hot.

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Well not exactly. Take the 20w50 for example. The chart has both 20w and 20 grades and the parameters defining them are different. Now you certainly could say a 10w30 is like a 10w when cold and like a SAE 30 when warm(and that probably is what you meant).

 

[G-MAN]

So much misinformation in this thread. All the "W" behind a given SAE grade means is that the oil has met the J300 cold cranking and cold pumping specs for that grade. Currently there are only six grades for which there are cold cranking and cold pumping specs: 0W, 5W, 10W, 15W, 20W and 25W. Of these six grades only one, SAE 20, also has "high temp" and "high temp/high shear" J300 requirements, thus it is the only grade which can have the same SAE grade on both sides of the "W", i.e., 20w20.

A multi-grade oil such as 10w30 means that the oil meets the cold cranking and cold pumping specs for an SAE 10W oil as well as the high temp and HTHS specs for an SAE 30.

 

[hominid7]

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Maybe it does, but I never thought of 20w50 as winter oil, unless maybe you live in Atlanta or some place similary down south.

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Since you mention it, my old VW Jetta required 20w50 as per the owners manual above 14*F, anything thinner in winter or summer would set the oil light off when the car was at operating temp. Actually it was not that other oils were too thin, rather that the VW oil pressure system was, how should we say, particular.

There were a few mornings down here in North Texas when my VW was covered with ice and the temp guage read 12*F that i had to cross my fingers when i turned the key, but it always started. Granted, that was a 1989 vintage car.

20W oil was used as a winter oil for years before the advent of multi-vis oils. It would not be advised in todays DOHC engines, but in older SOHC and flathead engines, it worked just great.

 

[Shannow]

20W-50 was winter oil, even in the Snowy mountains when I was younger.

I used 20W-50 with STP to fortify it for ages.

Then the thicker oils hit Oz, like 25W-60, 25W-70, 30W-70, and 40W-70 (the last few grades are indicative only, as there's no 30W, or 70.

 

[hominid7]

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What I never understood about that, is isn't 10

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It seems simple, but the more you think about it, the more confusing it is Try this:

A 10w30 is an oil that will not *thicken* any more than a SAE 10w oil at cold temps and will not *thin* more than a SAE30 would at operating temps.

All oils are thick when cold, but a 10w will be "less thick" than an oil rated SAE30 when cold.

All oils are thin when hot, but a SAE 30 will be "less thin" than an oil rated 10w when hot.

 

[theedge67]

Awesome explanation. I think that makes it much more clear for the masses!!

 

[Merkava_4]

hominid7's explanation seems to be the same as mine only worded different. I'm not saying mine is better; I'm just saying I don't see much difference.