How can an oil be rated at "0W"?

[Bob_B]

I've often wondered how a company can rate its oil as "0W". Per the usual definition of the oil's viscosity, the first number is derived from the amount of time, in seconds, that the oil takes to run through a controlled measuring device at a standard low temperature. Nothing can run through in 0 seconds, so where do the manufacturers get this number?

 

[d00df00d]

The number with the W after it is a winter rating. It indicates cold characteristics. It's not a weight.

 

[XS650]

 Originally Posted By: Bob_B

I've often wondered how a company can rate its oil as "0W". Per the usual definition of the oil's viscosity, the first number is derived from the amount of time, in seconds, that the oil takes to run through a controlled measuring device at a standard low temperature. Nothing can run through in 0 seconds, so where do the manufacturers get this number?

0w comes from SAE J300. SAE viscosity ratings such as 0W, 5W, etc are not actual viscosity numbers. They mean that the oil is within a range of viscosity that is spelled out in SAE J300. The actual units of viscosity used in J300 are centiStokes (cSt). The two xW tests are done at two different low temperature for each xW rating and neither test is done by timing the oil through a simple measuring device like in the olden daze. There are several ways to measure oil viscosity, timing it through a measuring device isn't the only way.

 

[nicrfe1370]

 Originally Posted By: XS650

 Originally Posted By: Bob_B

I've often wondered how a company can rate its oil as "0W". Per the usual definition of the oil's viscosity, the first number is derived from the amount of time, in seconds, that the oil takes to run through a controlled measuring device at a standard low temperature. Nothing can run through in 0 seconds, so where do the manufacturers get this number?

0w comes from SAE J300. SAE viscosity ratings such as 0W, 5W, etc are not actual viscosity numbers. They mean that the oil is within a range of viscosity that is spelled out in SAE J300. The actual units of viscosity used in J300 are centiStokes (cSt). The two xW tests are done at two different low temperature for each xW rating and neither test is done by timing the oil through a simple measuring device like in the olden daze. There are several ways to measure oil viscosity, timing it through a measuring device isn't the only way.

XS650, perfect answer. Accurate, simple, helpful. If only all questions were answered in such a manner.

 

[Drew2000]

So, will there ever be a oil rated lower than zero, like a -5w15 or a -10w10?

 

[dwendt44]

I'm guessing NOT. -5W-20 would be to confusing for the general public. They would likely come up with a new rating system or a 'code' name like 'sub-sero', 'sub-artic', or some such.

 

[Audi Junkie]

API moves the markers' specs downwards to make new oils better. Unless we see some serious global cooling, 5w being rated at -25f seems quite sufficient. Better cold-cranking will come as a result of usefull oil viscs being made thinner at op temps. The API system already reflects this to a degree, the allowable pumping limits for a 5w-20 are lower thana 5w-30 and 40 and so on.

 

[tom slick]

Just to clarify SAE viscosity numbers: (and to rant a bit) The numbers on the scale are relative and are don't correlate to an actual measurement, similar to the Fahrenheit temperature scale; 80*F doesn't mean anything other than it is cooler than 90*F. You can almost think of it as a rating or range of viscosity. It could be Aw-B, or 2563w-5632, or extra-light w - light and have the same meaning. The Xw (i.e. 0w) means the oil flows similar to a SAE "Ow" (bottom of the scale) viscosity when cold. The -XX (i.e. -20) means it flows similar to a SAE "20" when hot. It does not mean the oil is "thinner" or "lower weight" when cold or "thicker" or "higher weight" when hot, quite the opposite is true. This is also confused by having seperate engine oil and gear oil scales on the SAE chart. SAE 75w gear oil is not "thicker" than SAE 50 motor oil, in fact SAE 75w gear oil is about the same viscosity as SAE 10w to 20w motor oil. Similar to the Fahrenheit and Celsius temperature scales, 212*F is not "hotter" than 100*C, they are the same temperature. The "w" stands for "winter". I don't know why this is added to multi-grade oils but it is one more area of confusion in the SAE system. The ISO scale on the other hand does correlate to viscosity and only has one scale. An ISO 32 oil has a Kenematic viscosity of 32 at 104*F, measured the same way as they do in the SAE system. It doesn't matter if it is turbine oil, way oil, gear oil, etc it is always ISO viscosity 32. ISO 64 is always more viscous than ISO 32, they are on the same easy to understand scale. ISO 32 is about the same as SAE 75w gear oil or SAE 10W engine oil.

 

[Gary Allan]

How's this: The "W" designations are in increments of "5's" ...when they were able to recreate the stress and other criteria for the "5w" rating ..at -5F lower temps ..they needed to use a new number. They, following all the other standards for 20W, 10W, and 5w ...said "heck, looks like it's ZERO!". I imagine that this will morph to 00W or X0w in the future if the properties continue to extend into colder temps under current standards.

 

[Bob_B]

I got the following from an article on this forum. It seems to contradict some of the info above. Just wondering why... MULTI-VISCOSITY OILS Multi viscosity oils have polymers added to a light base (5W, 10W, 20W), which prevent the oil from thinning as much as it warms up. At cold temperatures the polymers are coiled up and allow the oil to flow as their low numbers indicate. As the oil warms up, the polymers begin to unwind into long chains that prevent the oil from thinning as much as it normally would. The result is that at 100 degrees C, the oil has thinned only as much as the higher viscosity number indicates. Another way of looking at multi-vis oils is to think of a 20W-50 as a 20 weight oil that will not thin more than a 50 weight would when hot.

 

[d00df00d]

 Originally Posted By: Bob_B

I got the following from an article on this forum. It seems to contradict some of the info above. Just wondering why...

Because it's sort of outdated and not true of all oils.

 

[Patman]

 Originally Posted By: Drew2000

So, will there ever be a oil rated lower than zero, like a -5w15 or a -10w10?

What they will probably do eventually is just make it much harder for an oil to qualify as a 0w, so some of the oils that are now rated as 0wXX under the current guidelines might only qualify as 5wXX under an updated system, and only the ones with really exceptional cold cranking numbers will get the 0w rating.

 

[wannafbody]

Some oils are rated for -20 to -59 degrees farenheit. Not sure their is much need for paasenger car oils that operate at colder temps. I could see some demand for heavy equipment that operates in Canada, Alaska and the artic circle though.

 

[tom slick]

 Originally Posted By: Bob_B

I got the following from an article on this forum. It seems to contradict some of the info above. Just wondering why... MULTI-VISCOSITY OILS Multi viscosity oils have polymers added to a light base (5W, 10W, 20W), which prevent the oil from thinning as much as it warms up. At cold temperatures the polymers are coiled up and allow the oil to flow as their low numbers indicate. As the oil warms up, the polymers begin to unwind into long chains that prevent the oil from thinning as much as it normally would. The result is that at 100 degrees C, the oil has thinned only as much as the higher viscosity number indicates. Another way of looking at multi-vis oils is to think of a 20W-50 as a 20 weight oil that will not thin more than a 50 weight would when hot.

The last sentence is a bit misleading but technically correct. It is a 20 when cold but its viscosity at that temperature is still much greater than a 50 at operating temperature.

 

[TwsT]

Please educate me. How come, for example, Amsoil ATM 10W30, a 10W oil can have a pour point of -50deg.C. But Amsoil XLM 5W20, a 5W oil gives a -43deg.C pour point? So which one performs better in very cold weather? Thanks.

 

[Nickdfresh]

I'm not the best to answer this, but I believe ATM 10W-30 is a PAO based synthetic, while XL uses Group III base stocks that cannot match the lower pour points and colder flow properties of Group IV/V syn oils... *edit: Which "performs better" will result in a big argument? Some will say that 10W-30 actually flows better than 5W-30 at very cold temps, for instance (less additives to the base oil I think?). And yet others will say that extreme cold flow properties are not that relevant at most winter temperatures and have little to do with how well it flows when you start your car in the morning unless you are in true Arctic conditions...

 

[d00df00d]

 Originally Posted By: TwsT

Please educate me. How come, for example, Amsoil ATM 10W30, a 10W oil can have a pour point of -50deg.C. But Amsoil XLM 5W20, a 5W oil gives a -43deg.C pour point? So which one performs better in very cold weather? Thanks.

Depends on how cold you mean. Below about -40 degrees C, ATM is the superior choice. Although it will be extremely thick in that temperature range, its superior base stocks will allow it to continue to flow. Around -30 degrees, the two oils should be fairly similar. From there up, XLM will be thinner.

 

[Shannow]

I'd like to see a different rating system. Operating viscosity (say at 110C), and either visc index, or visc at zero C, pour point or something. M1 0W-40 would be 14-186, 376-14, or 14 (something) Delvac MX 16-140, 738-16, or 14-33 Prolly the zeroC, 100C figures would give the best impression...and get rid of the believe that the oils get thicker when they get hotter.

 

[XS650]

 Originally Posted By: TwsT

Please educate me. How come, for example, Amsoil ATM 10W30, a 10W oil can have a pour point of -50deg.C. But Amsoil XLM 5W20, a 5W oil gives a -43deg.C pour point? So which one performs better in very cold weather? Thanks.

The SAE J300 tests used to rate the xW number for oils are good. Pour point is just noise introduced into the discussion. It's convenient because it's easy to do and may give a company a marketing edge with the gullible while conveying no useful information, sorta like the 4-ball test on engine oil. Pour point isn't part of the official SAE or API rating system. The two official SAE J300 tests evaluate cold weather pumpability and cranking resistance. Amsoil doesn't always follow API or SAE standards. If they have the API donut on the container, they probably do follow the standard for those oils. I'm not implying their oil isn't good.

 

[XS650]

 Originally Posted By: Shannow

I'd like to see a different rating system. Operating viscosity (say at 110C), and either visc index, or visc at zero C, pour point or something. M1 0W-40 would be 14-186, 376-14, or 14 (something) Delvac MX 16-140, 738-16, or 14-33 Prolly the zeroC, 100C figures would give the best impression...and get rid of the believe that the oils get thicker when they get hotter.

I have long thought that something like that would be a major improvement. My preference would be an oil with two numbers. A cold weather number in degrees C that was the lowest temperature that an oil met a consistent pair of tests for pumpability and cranking without any mickey mousing of the numbers for various temperatures like SAE J300 does now for low temperature cranking. Then a high temperature number (100C is OK with me) based on the actual viscosity in cSt like is done for ISO viscosities, except at 100C.