UNEEQ
17th February 2010, 11:06 AM
Hi all,
So for the past few days - week I've been trying to decide on what oil I'm planning on using for my car since it's coming up for a 5,000 drain (and I want to get rid of whatever crap... err sorry... "not-as-high-performace-as-what-I'd-like" oil the dealer put in the car last)
BUT.... I've run into a good number of misconceptions and basically a whole load of random bullshit about what the details of an oil means. So I've done a good deal of searching and reading (and discussing with my workmates.), and one of them sent me to a site which has a great factual explaination (without the confusion that you'd get from wikipedia or some other technical sites I've been to).
In summary:
I think the main point here is that the first number is NOT a viscosity rating per say but it does define the flow at cold crank. The w does not stand for weight, but is more of a code for winter. It applies to the first number to show it's not an SAE rating and that the oil is a multigrade. The final number is the SAE viscosity rating.
I could ramble more, but I'll let the article do the full explaination. There is more after the excerpt, but it tells you to "buy the book"?!
Cheers
Todd
Undertanding Multi-Viscosity Oils
When speaking of the properties of a motor oil, viscosity is of tremendous importance. Unfortunately, it also an area that is very confusing. The viscosity of an oil refers to its relative resistance to flow at differing temperatures. As has been previously mentioned, an oil must not only be "thin" enough to flow well at low temperatures, it must also remain "thick" enough to maintain adequate protection at high temperatures.
Ideally, an oil will maintain a consistent viscosity over a wide temperature range. The viscosity index of an oil is a measure of its tendency to change viscosity with temperature changes. The higher the viscosity index (VI) the more consistent an oil's viscosity is with temperature changes.
Monograde Oils
Monograde oils such as 30 weight oils are designed for consistent temperature applications. For instance, you will find that most older lawn tractors and mowers call for a straight 30 weight oil (SAE 30). This is because it is assumed that these will be operating mainly in warm temperature summer months.
So, if you take a look at their viscosity index, you'll notice that most monograde oils have a low VI number. This implies that as you cool the oil it will thicken quite a bit. However, this is ok, because the oil is designed to only be used under warm conditions. Cold temperature thickening will not be an issue.
According to SAE J300 standards, to be classified as a certain SAE viscosity, an oil is heated to 100 degrees C (212 degrees F). It's kinematic viscosity at this temperature is measured. If it falls within a certain range it is classified as a particular viscosity. For instance, an SAE 30 oil must have a kinematic viscosity at 100 degrees C of between 9.3 and 12.5 cSt (centistokes).
Multi-Viscosity (Multi-Grade) Oils
Multi-viscosity (multi-grade) oils such as 0w30, 5w30, 10w40 and so on are oils, which are designed for applications where temperature changes may be significant. For instance, multi-viscosity oils might be used in northern US climates where temperatures can be -20 degrees F in the winter and +95 degrees F in the summer.
However, that does not mean they cannot be used for applications where the temperature remains more consistent. The fact is, monograde oils are becoming much less common as multi-viscosity oils are being substituted in applications which traditionally called for a monograde oil.
Nevertheless, monograde oils are still used in many super high performance racing applications, construction equipment that is used in only summer months and industrial engines that are kept indoors at a constant temperature all year round.
What Do the Numbers Mean?
Most people believe that a 5w30 oil is good for cold weather use because it is a "5 weight" oil in cold temperatures and a "30 weight" oil at high temperatures. On the surface this might seem to make a certain amount of sense. Naturally, a "5 weight" oil would flow better than a "30 weight" oil. This would make it ideal for cold temperature operation.
Nevertheless, this is a profound misunderstanding of what the labeling means. The two numbers really have little to do with each other. The final number is based upon the kinematic viscosity of the oil at 100 degrees C, as we discussed for monograde oils.
So, if a multi-grade oil, when heated to 100 degrees C, falls within a certain kinematic viscosity range it is classified as a certain SAE grade (the last number - like the "30" in 5w30). In other words, the kinematic viscosity of a 5w30 multi-viscosity oil falls within the same range at 100 degrees C as a monograde SAE 30 weight oil does.
5w is NOT 5 "weight"
In contrast to a monograde oil, a multi-viscosity oil also has to meet a "High Temperature/High Shear" requirement, but I'll talk about that in a minute. Let's talk about the "w" number for a moment. This first number (the "5" in 5w30) is only a relative number which basically indicates how easily it will allow an engine to "turn over" at low temperatures. It is NOT a viscosity reference. In other words, a 10w30 is NOT a 10 weight oil in cold temperatures and a 30 weight oil in warm temperatures.
In fact, since SAE viscosity classifications only apply to an oil at 100 degrees C, it doesn't even make sense to label it as a certain SAE viscosity at any temperature other than 100 degrees C.
Besides, if you thought about it for a second, it wouldn't make sense for a 10w30 oil to be a 10 weight oil in the cold and a 30 weight oil in warm temperatures. What liquid do you know of that gets "thicker" as its temperature increases or "thinner" as the temperature decreases?
I would venture to say you probably can't come up with one. This holds true for motor oil as well. If a 10w30 was a 30 weight oil at 100 degrees C and a 10 weight oil at cold temperatures, that would mean it "thinned out" as the temperature dropped. That just doesn't make any sense considering what we know about liquids. It just doesn't happen like that.
The fact is that a 5w30 motor oil is thicker in cold temperatures than in warm temperatures. In fact, you could easily demonstrate this for yourself. Have you ever tried to pour oil out of the bottle in the winter - even a winter rated multi-viscosity oil? It pours more slowly, doesn't it? That's because the cold temperature "thickens" the oil.
However, a 5w30 motor oil will be thinner than a 10w30 motor oil when subjected to the same low temperature conditions - because the "W" number is lower. This is an indication of better cold weather performance. In other words, a 5w30 flows better in cold weather than a 10w30 motor oil will. Think of the "W" as a "winter" classification instead of a "weight" classification.
Classifying the "W" Rating
Results from the Cold Crank Simulator (CCS) and Mini-Rotary Viscometer (MRV) tests are used to determine the oil's "W" grade. The better the engine "startability" of the oil at low temperature, the lower the W classification. Each W grade must meet certain "startability" requirements at a specified temperature.
So for the past few days - week I've been trying to decide on what oil I'm planning on using for my car since it's coming up for a 5,000 drain (and I want to get rid of whatever crap... err sorry... "not-as-high-performace-as-what-I'd-like" oil the dealer put in the car last)
BUT.... I've run into a good number of misconceptions and basically a whole load of random bullshit about what the details of an oil means. So I've done a good deal of searching and reading (and discussing with my workmates.), and one of them sent me to a site which has a great factual explaination (without the confusion that you'd get from wikipedia or some other technical sites I've been to).
In summary:
I think the main point here is that the first number is NOT a viscosity rating per say but it does define the flow at cold crank. The w does not stand for weight, but is more of a code for winter. It applies to the first number to show it's not an SAE rating and that the oil is a multigrade. The final number is the SAE viscosity rating.
I could ramble more, but I'll let the article do the full explaination. There is more after the excerpt, but it tells you to "buy the book"?!
Cheers
Todd
Undertanding Multi-Viscosity Oils
When speaking of the properties of a motor oil, viscosity is of tremendous importance. Unfortunately, it also an area that is very confusing. The viscosity of an oil refers to its relative resistance to flow at differing temperatures. As has been previously mentioned, an oil must not only be "thin" enough to flow well at low temperatures, it must also remain "thick" enough to maintain adequate protection at high temperatures.
Ideally, an oil will maintain a consistent viscosity over a wide temperature range. The viscosity index of an oil is a measure of its tendency to change viscosity with temperature changes. The higher the viscosity index (VI) the more consistent an oil's viscosity is with temperature changes.
Monograde Oils
Monograde oils such as 30 weight oils are designed for consistent temperature applications. For instance, you will find that most older lawn tractors and mowers call for a straight 30 weight oil (SAE 30). This is because it is assumed that these will be operating mainly in warm temperature summer months.
So, if you take a look at their viscosity index, you'll notice that most monograde oils have a low VI number. This implies that as you cool the oil it will thicken quite a bit. However, this is ok, because the oil is designed to only be used under warm conditions. Cold temperature thickening will not be an issue.
According to SAE J300 standards, to be classified as a certain SAE viscosity, an oil is heated to 100 degrees C (212 degrees F). It's kinematic viscosity at this temperature is measured. If it falls within a certain range it is classified as a particular viscosity. For instance, an SAE 30 oil must have a kinematic viscosity at 100 degrees C of between 9.3 and 12.5 cSt (centistokes).
Multi-Viscosity (Multi-Grade) Oils
Multi-viscosity (multi-grade) oils such as 0w30, 5w30, 10w40 and so on are oils, which are designed for applications where temperature changes may be significant. For instance, multi-viscosity oils might be used in northern US climates where temperatures can be -20 degrees F in the winter and +95 degrees F in the summer.
However, that does not mean they cannot be used for applications where the temperature remains more consistent. The fact is, monograde oils are becoming much less common as multi-viscosity oils are being substituted in applications which traditionally called for a monograde oil.
Nevertheless, monograde oils are still used in many super high performance racing applications, construction equipment that is used in only summer months and industrial engines that are kept indoors at a constant temperature all year round.
What Do the Numbers Mean?
Most people believe that a 5w30 oil is good for cold weather use because it is a "5 weight" oil in cold temperatures and a "30 weight" oil at high temperatures. On the surface this might seem to make a certain amount of sense. Naturally, a "5 weight" oil would flow better than a "30 weight" oil. This would make it ideal for cold temperature operation.
Nevertheless, this is a profound misunderstanding of what the labeling means. The two numbers really have little to do with each other. The final number is based upon the kinematic viscosity of the oil at 100 degrees C, as we discussed for monograde oils.
So, if a multi-grade oil, when heated to 100 degrees C, falls within a certain kinematic viscosity range it is classified as a certain SAE grade (the last number - like the "30" in 5w30). In other words, the kinematic viscosity of a 5w30 multi-viscosity oil falls within the same range at 100 degrees C as a monograde SAE 30 weight oil does.
5w is NOT 5 "weight"
In contrast to a monograde oil, a multi-viscosity oil also has to meet a "High Temperature/High Shear" requirement, but I'll talk about that in a minute. Let's talk about the "w" number for a moment. This first number (the "5" in 5w30) is only a relative number which basically indicates how easily it will allow an engine to "turn over" at low temperatures. It is NOT a viscosity reference. In other words, a 10w30 is NOT a 10 weight oil in cold temperatures and a 30 weight oil in warm temperatures.
In fact, since SAE viscosity classifications only apply to an oil at 100 degrees C, it doesn't even make sense to label it as a certain SAE viscosity at any temperature other than 100 degrees C.
Besides, if you thought about it for a second, it wouldn't make sense for a 10w30 oil to be a 10 weight oil in the cold and a 30 weight oil in warm temperatures. What liquid do you know of that gets "thicker" as its temperature increases or "thinner" as the temperature decreases?
I would venture to say you probably can't come up with one. This holds true for motor oil as well. If a 10w30 was a 30 weight oil at 100 degrees C and a 10 weight oil at cold temperatures, that would mean it "thinned out" as the temperature dropped. That just doesn't make any sense considering what we know about liquids. It just doesn't happen like that.
The fact is that a 5w30 motor oil is thicker in cold temperatures than in warm temperatures. In fact, you could easily demonstrate this for yourself. Have you ever tried to pour oil out of the bottle in the winter - even a winter rated multi-viscosity oil? It pours more slowly, doesn't it? That's because the cold temperature "thickens" the oil.
However, a 5w30 motor oil will be thinner than a 10w30 motor oil when subjected to the same low temperature conditions - because the "W" number is lower. This is an indication of better cold weather performance. In other words, a 5w30 flows better in cold weather than a 10w30 motor oil will. Think of the "W" as a "winter" classification instead of a "weight" classification.
Classifying the "W" Rating
Results from the Cold Crank Simulator (CCS) and Mini-Rotary Viscometer (MRV) tests are used to determine the oil's "W" grade. The better the engine "startability" of the oil at low temperature, the lower the W classification. Each W grade must meet certain "startability" requirements at a specified temperature.