Oil question

[GeorgeB.]

Completely unrelated to any other thread existing at this current time, what does the "w" in motor oil stand for?

Asking for a friend, obviously.

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Current: '99 Fazer 600 | '99 Range Rover P38 4.6 HSE
Previous: Keeway TX125 | CBF 125 | CB400SF Project Big One
CBT 04/12/12 | Theory 03/12/13 | MOD 1 06/01/14 | MOD 2 13/01/14

[fatjames]

My guess is 'weight'

[GeorgeB.]

Internet gives conflicting answers of "weight" and "winter".
____________________
Current: '99 Fazer 600 | '99 Range Rover P38 4.6 HSE
Previous: Keeway TX125 | CBF 125 | CB400SF Project Big One
CBT 04/12/12 | Theory 03/12/13 | MOD 1 06/01/14 | MOD 2 13/01/14

[fatjames]

oh oh ! now I see what you've done there!

[Aff]

Winter
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Electric Bike Project

[talkToTheHat]

In the context of oils defined Xw-Y, for example 10w-40 the w is the winter or cold viscosity. 10w oil (and it can be found as a straight 10w single grade) looks a lot like 10w-40, whereas a straight 10 weight oil is a very light 'sewing machine' oil.
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Bandit. does. everything.

[weasley]

It is "winter". This is defined by the Society of Automtive Engineers, who are the "SAE" of SAE xW-yy.
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[Supermoto_Fan]

Seen the opie oils competition by any chance?

In which case I've realised I've cocked it up
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Yamaha MT-09 - Triple powerrrr

[Supermoto_Fan]

Seen the opie oils competition by any chance?

In which case I've realised I've cocked it up
____________________
Yamaha MT-09 - Triple powerrrr

[Val]

The number with or without letter W means the grade of the oil. There are 11 viscosity grades: 0W, 5W, 10W, 15W, 20W, 25W, 20, 30, 40, 50, and 60. These numbers are often referred to as the "weight" of a motor oil, and single-grade motor oils are often called "straight-weight" oils. The lower the number before W you have oil that can work on coolest winter temperature. Again the higher the grade number without W means the oil can work fine in higher summer temperatures. You cannot have your cake and eat it - nobody can produce good oilthat cover all temperatures like 0W-60. So in hot climate countries you buy 20W-60 oil and in realy cold places you use 0W-30 oils. And of course there are engine limitations here to what oil your engine can accept.

Note you may have oil without W when we have single grade oil like oil 40 for example.

In modern cars we use multi-grade oil so that we can drive the car in the winter and in the summer without changing the oil.

Say W is winter but its related to the number cannot be used alone 10W oil grade means absolute viscosity of the oil:

Absolute Viscosity is a measure of a fluid's internal resistance to flow and may be thought of as a measure of fluid friction and of the oil's film strength to support a load. It measures viscosity and pumpability of oil when the temperature is cold in the winter.

The second number of the multi-grade oil is oil Kinematic Viscosity:

Kinematic Viscosity is a measure of the fluids resistance to flow and shear under the forces of gravity, or how easily the oil flows to the different parts of the engine when the engine and oil are hot. This measurement influences such factors as fuel consumption, valve-train wear and bearing protection.

For example oil with 10W-40 has Absolute Viscosity (10W) maximum cold cranking 7 000 at temperature -25°C and maximum cold pumping of 60 000 at temperature -30°C

And Kynematic Viscosity Minimum 12.5 and Maximum <16.3

as per SAE Viscosity Grades for Engine Oils (SAE J300) - December 1999

https://www.widman.biz/English/Tables/J300.html

Cold cranking viscosity simulates the viscosity of an oil in crankshaft bearings during start up on a cold winter morning. The test determines if an engine can be cranked over fast enough to start under extreme cold ambient conditions. ASTM Method D 5293 simulates an oil's cranking resistance when cold, and thus indicates the lowest temperature at which an engine is likely to start.

Cold pumpability measures the resistance of an oil to pumping through the engine after a cold start. The most widely used test is ASTM D 4684. If an oil's viscosity becomes too high, pumping will be hindered with possible cavitation issues. Viscosity here becomes an important factor in determining whether the engine runs with sufficient lubrication after starting in severe cold conditions. The Cold Pumpability test is always conducted at 5°C colder than the Cold Cranking test to ensure the pump can deliver the oil to the bearings.
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[weasley]

Mostly right, but with some updates.

There is now an SAE 16 grade, to accommodate the increasing need for fuel economy and reduced CO2 emissions.

Mostly Americans say "weight".

The non-W (second) number is not about ambient temperature, but more about engine operating temperature.

And in most temperate places you don't buy different oils for different seasons or climates - that's the whole point of a multi-grade. For example if you have a VW car and run on long service, you use a 5W-30. That's it, all year, for (up to) 2 years, in Sweden and in Spain. The correct viscosity to use these days is more about efficiency and durability than about the weather.

You also missed out the very important HTHS requirements. This viscosity test is conducted at high shear rate (10^6 /s) and high temperature (150°C) to simulate crank bearing conditions. It is used as a proxy for fundamental engine protection and is the basis for many oil specifications, including ACEA and OEMs, as well as in the SAE viscosity grades.

Finally, being picky, the cold pumpability test not only gives an absolute viscosity number, but it is important that there is no yield stress (regardless of what viscosity number you get). This is important because a cold oil may pump OK, but may exhibit a semi-solidification (or gelling) effect when cold and stationary that can prevent oil flowing to the oil pickup, meaning the oil pump can suck a 'crater' out of the surface of the oil which doesn't in-fill quickly enough, leading to oil starvation.

TL;DR - "W" stands for "winter".
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