Members: Please clear up something for me in my infinite ignorance on lubricants. On a multi viscosity oil rating, say 5/40.....is the "true" viscosity of that oil 5, while the 40 refers to it's cushioning properties rather than actual viscosity rating? thanks bb
viscosity reference
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LD1
Epic Contributor
40 is the actual viscosity of the oil while it is working in your engine.
The 5 refers to its cold flow properties. Which means it flows like 5w when it is cold on engine start up, and flows like a 40w once it is warmed up.
The 5 refers to its cold flow properties. Which means it flows like 5w when it is cold on engine start up, and flows like a 40w once it is warmed up.
BigBubba,
LD1 is right, the viscosity is 40 measured at 100c. It has cold flow propreties of 5 until warm up to 100c. If I can get it to come through, check out the Oil Bible pdf file it has some great info. Must be too big a file. If yoou think about it though no fluid gets thicker in heat so theidea that oil starts at 5 viscosity and goes to 40 when it is hot really can not happen.
Take care-TPS
LD1 is right, the viscosity is 40 measured at 100c. It has cold flow propreties of 5 until warm up to 100c. If I can get it to come through, check out the Oil Bible pdf file it has some great info. Must be too big a file. If yoou think about it though no fluid gets thicker in heat so theidea that oil starts at 5 viscosity and goes to 40 when it is hot really can not happen.
Take care-TPS
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LD1 & TPS: thanks for you info. Please check out the attached discussion of "synthetic oils" on the attached forum thread under Kubota tractors discussion forum. In that forum I go by commander k....I may have become a bit hot headed, but let me know what you think on the subject.....according to them, your viscosity definition is incorrect. It's easy for someone new to that forum to reply.....many thanks. bb
Synthetic engine oil
Synthetic engine oil
Mace Canute
Elite Member
From Wikipedia:
"The temperature range the oil is exposed to in most vehicles can be wide, ranging from cold temperatures in the winter before the vehicle is started up to hot operating temperatures when the vehicle is fully warmed up in hot summer weather. A specific oil will have high viscosity when cold and a lower viscosity at the engine's operating temperature. The difference in viscosities for most single-grade oil is too large between the extremes of temperature. To bring the difference in viscosities closer together, special polymer additives called viscosity index improvers, or VIIs are added to the oil. These additives are used to make the oil a multi-grade motor oil, however it is possible to have a multi-grade oil without the use of VIIs. The idea is to cause the multi-grade oil to have the viscosity of the base grade when cold and the viscosity of the second grade when hot. This enables one type of oil to be generally used all year. In fact, when multi-grades were initially developed, they were frequently described as all-season oil. The viscosity of a multi-grade oil still varies logarithmically with temperature, but the slope representing the change is lessened. This slope representing the change with temperature depends on the nature and amount of the additives to the base oil.
The SAE designation for multi-grade oils includes two viscosity grades; for example, 10W-30 designates a common multi-grade oil. The two numbers used are individually defined by SAE J300 for single-grade oils. Therefore, an oil labeled as 10W-30 must pass the SAE J300 viscosity grade requirement for both 10W and 30, and all limitations placed on the viscosity grades (for example, a 10W-30 oil must fail the J300 requirements at 5W). Also, if an oil does not contain any VIIs, and can pass as a multi-grade, that oil can be labeled with either of the two SAE viscosity grades. For example, a very simple multi-grade oil that can be easily made with modern baseoils without any VII is a 20W-20. This oil can be labeled as 20W-20, 20W, or 20. Note, if any VIIs are used however, then that oil cannot be labeled as a single grade.
The real-world ability of an oil to crank or pump when cold is potentially diminished soon after it is put into service. The motor oil grade and viscosity to be used in a given vehicle is specified by the manufacturer of the vehicle (although some modern European cars now have no viscosity requirement), but can vary from country to country when climatic or fuel efficiency constraints come into play."
"The temperature range the oil is exposed to in most vehicles can be wide, ranging from cold temperatures in the winter before the vehicle is started up to hot operating temperatures when the vehicle is fully warmed up in hot summer weather. A specific oil will have high viscosity when cold and a lower viscosity at the engine's operating temperature. The difference in viscosities for most single-grade oil is too large between the extremes of temperature. To bring the difference in viscosities closer together, special polymer additives called viscosity index improvers, or VIIs are added to the oil. These additives are used to make the oil a multi-grade motor oil, however it is possible to have a multi-grade oil without the use of VIIs. The idea is to cause the multi-grade oil to have the viscosity of the base grade when cold and the viscosity of the second grade when hot. This enables one type of oil to be generally used all year. In fact, when multi-grades were initially developed, they were frequently described as all-season oil. The viscosity of a multi-grade oil still varies logarithmically with temperature, but the slope representing the change is lessened. This slope representing the change with temperature depends on the nature and amount of the additives to the base oil.
The SAE designation for multi-grade oils includes two viscosity grades; for example, 10W-30 designates a common multi-grade oil. The two numbers used are individually defined by SAE J300 for single-grade oils. Therefore, an oil labeled as 10W-30 must pass the SAE J300 viscosity grade requirement for both 10W and 30, and all limitations placed on the viscosity grades (for example, a 10W-30 oil must fail the J300 requirements at 5W). Also, if an oil does not contain any VIIs, and can pass as a multi-grade, that oil can be labeled with either of the two SAE viscosity grades. For example, a very simple multi-grade oil that can be easily made with modern baseoils without any VII is a 20W-20. This oil can be labeled as 20W-20, 20W, or 20. Note, if any VIIs are used however, then that oil cannot be labeled as a single grade.
The real-world ability of an oil to crank or pump when cold is potentially diminished soon after it is put into service. The motor oil grade and viscosity to be used in a given vehicle is specified by the manufacturer of the vehicle (although some modern European cars now have no viscosity requirement), but can vary from country to country when climatic or fuel efficiency constraints come into play."
BB,
According to the way they have defined it then a 0w-40 oil is a 0 weight oil. I would disagree it is a 40 wt oil that has flow characteristics of 0 when cold.
No oil is going to get thicker when it heats up so who would ever use a 0 wt oil if their definition were correct? In addition, of course a 30 weight oil is really 30w-30 because it has a flow charateristic of 30 when cold and a weight of 30 hence the 30w-30 or shortened to 30 weight or viscosity, not to be confused with viscosity index in which higher is better because less change in the oil viscosity over temperature ranges. Having said all of this the additive packages are very important. BB I agree with you in those posts that I read and think they are misinformed.
Take care-TPS
According to the way they have defined it then a 0w-40 oil is a 0 weight oil. I would disagree it is a 40 wt oil that has flow characteristics of 0 when cold.
No oil is going to get thicker when it heats up so who would ever use a 0 wt oil if their definition were correct? In addition, of course a 30 weight oil is really 30w-30 because it has a flow charateristic of 30 when cold and a weight of 30 hence the 30w-30 or shortened to 30 weight or viscosity, not to be confused with viscosity index in which higher is better because less change in the oil viscosity over temperature ranges. Having said all of this the additive packages are very important. BB I agree with you in those posts that I read and think they are misinformed.
Take care-TPS
RalphVa
Super Member
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I worked in the lube oil industry for 31 years as a chemical engineer. A 10w-40 oil is one that meets 40w criteria at 100 C (212 F), which is near the temperature that it runs at in the sump of your engine when fully warmed up. The 10w is measured at some other temperature, usually some lower temperature that represents what your engine oil might be at in the winter time. Even a 0w-30 oil will be heavier at startup than at operating temperature though.
Imperial Oil research once did some experiments with a car in a -40 C/F room overnight. They started the engine and filmed the transparent overhead valve cover. On any oil other than a 0w-xxx oil, there would be a significant amount of smoking underneath the valve cover, which means that the oil left there was being smoked off on startup because new oil wasn't getting up there. This was the case EXCEPT for 0w-xxx oil.
In another test by Sunoco research, they tried din oil and Mobil 1 (probably 5w-xxx or 0w-xxx). The engines with Mobil 1 showed NO valve train wear over the test period; whereas, dino oil let some wear occur on the valve train.
Use whatever you owner's manual says for the upper viscosity range but buy the lower other range, e.g. a 0w-30 is better than a 5w-30 and both better than a 10w-30 for protecting that valve train on startup. In general, xxw-20 oils are good for gasoline engines, and xxw-30 oils are good for diesels. I use 0w-30 in all my engines now: Mobil 1 of course.
Ralph
Imperial Oil research once did some experiments with a car in a -40 C/F room overnight. They started the engine and filmed the transparent overhead valve cover. On any oil other than a 0w-xxx oil, there would be a significant amount of smoking underneath the valve cover, which means that the oil left there was being smoked off on startup because new oil wasn't getting up there. This was the case EXCEPT for 0w-xxx oil.
In another test by Sunoco research, they tried din oil and Mobil 1 (probably 5w-xxx or 0w-xxx). The engines with Mobil 1 showed NO valve train wear over the test period; whereas, dino oil let some wear occur on the valve train.
Use whatever you owner's manual says for the upper viscosity range but buy the lower other range, e.g. a 0w-30 is better than a 5w-30 and both better than a 10w-30 for protecting that valve train on startup. In general, xxw-20 oils are good for gasoline engines, and xxw-30 oils are good for diesels. I use 0w-30 in all my engines now: Mobil 1 of course.
Ralph
Hematite
Gold Member
Despite what you think or believe or have "heard", the Wikipedia definition is correct, always has been always will be. A 10W-30 oil IS a 10 weight base stock oil with viscosity improvers, aka plasticizers, that cause the oil to thicken when heated and to equal a higher viscocity oil than the base stock.
If you and BB have other information, post a link that contradicts the Wikipedia and every other definition of multi viscosity oils so we can see who is truly misinformed.
Hematite
Gold Member
Well, I went to your source, the Engine Oil Bible and it specifically states exactly what the Wikipedia definition states:
Viscosity and Viscosity Index (VI).
The proper viscosity is the single most important criteria of a lubricating oil. The basic performance of machinery is based on the viscosity of the lubricant. Viscosity is, if you like, the resistance to the flowability of the oil. The thicker an oil, the higher its viscosity. The chart on the right shows a rough guide to ambient temperatures vs oil viscosity performance in both multigrade (top half) and single grade (lower half) oils.
Multigrade oils work by having a polymer added to a light base oil which prevents the oil from thinning too much as it warms up. At low temperatures, the polymers are coiled up and allow the oil to flow as it's low number (W number) indicates. As the oil heats up, the polymers unwind into long chains which prevent the oil from thinning as much as it normally would. The result is that at 100ｰC, the oil has thinned only as much as it's higher rating. Think of it like this: a 10W30 oil is a 10-weight oil that will not thin more than a 30-weight oil when it gets hot.
bp fick
Super Member
I admit it. I have no intelligent or scientifically based information about oil, viscosity or performance with which to remark, HOWEVER...
Wikipedia
Wikipedia is NOT a reliable source. At the university level, no Wikipedia quotes or primary sourcing are permitted. The reason is simple. Anyone can post on it. Quoting from Wikipedia and proclaiming "there, that is the fact" is, in fact, without credibility whatsoever. Even high school student know that. Shame.
Wikipedia
Wikipedia is NOT a reliable source. At the university level, no Wikipedia quotes or primary sourcing are permitted. The reason is simple. Anyone can post on it. Quoting from Wikipedia and proclaiming "there, that is the fact" is, in fact, without credibility whatsoever. Even high school student know that. Shame.
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