what does w mean in 10w40 oil

730virgil · Jan 26, 2017

tuesday night mrs 730 and i were watching a tv show The Wall.
a question was asked what does the w mean in 10w40 engine oil. they gave 4 choices winter,weight,water i don't remember the last one.
i said that's easy weight Mrs 730 thought that sounded right too. the contestant said weight the host said that is wrong the w in oil stands for winter.
what do you guys think?

docmirror · Jan 26, 2017

Winter.

Always has been, always will be.

mj · Jan 26, 2017

Well, I reckon that I've been wrong-headed then for over 50 years :shock: 'cause I always thought that by knowing the weight it was assumed that you would know what to use it for!

da.bees · Jan 26, 2017

Maybe it should say WW (winter weight)and there would be no confusion.

centash · Jan 27, 2017

Means it flows like straight 10 grade oil in the winter, thus 10w. Ben

MarkB_MI · Jan 27, 2017

"SAE 30" is 30 weight. Note there's no "W".

Hence "SAE 10W-30" means "same as SAE 10 in the winter, same as SAE 30 at operating temperature."

Jim PA · Jan 27, 2017

I may be wrong but I believe that the viscosity would be more like 30 weight in 0C until it reached operating temperature. At the point of operating temperature or calibrated temp of 100C it would flow more like 10 weight oil.

Mike M · Jan 27, 2017

Interesting thing about 10w40 oil. GM used to recommend it. Then they found out it was responsible for a lot of extra carbon forming on top of the pistons. They came out with a bulletin saying to start using 10w30

Spudm · Jan 27, 2017

According to Google:
In a 10w-40 for example the 10w bit (W = winter, not weight or watt or anything else for that matter) simply means that the oil must have a certain maximum viscosity/flow at low temperature. The lower the "W" number the better the oil's cold temperature/cold start performance.

Steven-Id · Jan 27, 2017

This is for different weight but explains pretty good.

Steven
Untitled URL Link

GVSII · Jan 27, 2017

(quoted from post at 06:49:45 01/27/17) Interesting thing about 10w40 oil. GM used to recommend it. Then they found out it was responsible for a lot of extra carbon forming on top of the pistons. They came out with a bulletin saying to start using 10w30

Back in the late '70s,early '80s a GM engineer said "10W40 never should have seen the light of day".Sounds like they'er still not sure!

Richard from SE AZ · Jan 27, 2017

I had read somewhere that WD meant " Water Displacement". That is why it can be used in a wet distributer cap to dry it and I have used it to do just that.

pete 23 · Jan 27, 2017

The 10W rating part of the oil has the viscosity measured at a lower temperature. That temperature can vary depending on the W rating. I think it is in the 10 degree F. area but could not find the information for sure. The 40 degree rating is taken at 100 degrees C. (210 F. I think). So, you start with a low viscosity oil, add pour point depresents if necessary to reach the W number flow desired , and add viscosity index improvers to reach the flow desired at the 40 rating. The greater the distance between the two numbers, the more additives added to reach their goal. Those additives are what shear at high temperatures and change the properties of the oil. More carbon, more sludge, thinner oil, etc.

what does w mean in 10w40 oil

730virgil

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docmirror

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mj

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da.bees

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centash

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MarkB_MI

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Jim PA

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Mike M

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Spudm

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Steven-Id

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GVSII

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Richard from SE AZ

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pete 23

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