Viscosity- what does it mean?
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Viscosity- what does it mean?
Viscosity is the measure of the flowability of oil and its property to shear, develop and maintain a certain amount of shearing stress dependent on flow and to maintain resistance to flow. All oils will thin as they reach operating temperatures. With that in mind, how does a 10w-30 work? Start with a 10 weight basestock and add polymers. Polymers are like little coil springs that when cold are coiled tightly and offer little resistance to flow. When exposed to heat, they uncoil and resist flow thereby thickening the oil. So if we add the right amount of polymers to the 10 weight oil to offer the same resistance of a 30 weight oil at temp, we have made a 10w-30 oil. So, a straight 30w and a 10w-30 will have the same relative thickness at temp.
Some folks have asked about using a 10w-30 instead of a 5w-30 for summer. They both will have the same viscosity at temp but the 5w-30 will flow easier at cold start up. The 5w-30 will have more polymers and polymers can breakdown in a high heat environment. If you don't need the cold start 5w, stay with the 10w-30, it is more stable.
Some folks have asked about using a 10w-30 instead of a 5w-30 for summer. They both will have the same viscosity at temp but the 5w-30 will flow easier at cold start up. The 5w-30 will have more polymers and polymers can breakdown in a high heat environment. If you don't need the cold start 5w, stay with the 10w-30, it is more stable.
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Viscosity- what does it mean?
OK, so less polymers is better. They are more or less one of the necessary evils that gets added to the base oil in order to increase its effectiveness over a greater range of ambient temperatures (at least that's what I think is going on).
So can we therefore draw the following conclusions:
1) Using oils with lower differences b/t their winter weight and 'hot' weight is better, all other things being equal?
2) If yes to #1, then wouldn't it be a better idea to change up on your grade of oil at each oil change interval - basing the grade on the temperatures you expect to encounter within the next 2 or 3 months - rather than trying to select one grade of oil to get you through all four seasons which naturally will require a larger gap b/t the winter weight and hot weight of the oil?
3) Taking it a step further, if conditions allow for it, wouldn't using a straight weight oil be the ideal thing to do?
So can we therefore draw the following conclusions:
1) Using oils with lower differences b/t their winter weight and 'hot' weight is better, all other things being equal?
2) If yes to #1, then wouldn't it be a better idea to change up on your grade of oil at each oil change interval - basing the grade on the temperatures you expect to encounter within the next 2 or 3 months - rather than trying to select one grade of oil to get you through all four seasons which naturally will require a larger gap b/t the winter weight and hot weight of the oil?
3) Taking it a step further, if conditions allow for it, wouldn't using a straight weight oil be the ideal thing to do?
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Viscosity- what does it mean?
#1. Yes, that is correct
#2. Not necessarily. Too much is said about viscosity and the supposed advantages. Did you know that a 15w-40 is thinner at temp than a 10w-30 at 70F? Unless you live in an area that gets below zero degrees there is not much concern about the basestock weight. Most 10w-30's have cold flow rates well below zero.
#3. There are no advantages to the straight weight oils other than no polymers exist for the thicksotropic. But there are significant advantages for the multi-weights.
#2. Not necessarily. Too much is said about viscosity and the supposed advantages. Did you know that a 15w-40 is thinner at temp than a 10w-30 at 70F? Unless you live in an area that gets below zero degrees there is not much concern about the basestock weight. Most 10w-30's have cold flow rates well below zero.
#3. There are no advantages to the straight weight oils other than no polymers exist for the thicksotropic. But there are significant advantages for the multi-weights.
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Viscosity- what does it mean?
Good topic Flash. Do you want to take it a bit further and include Group III and IV synthetics?
It's my understanding that synthetic's contain less 'fractions' than conventional motor oils' and contain their viscosity over a much wider temperature range. So they are less dependant or perhaps need no assistance at all from polymer's to stay in viscosity grade.
You probably know where I'm going with this...
What I'd like to know is since we now know that Group II and II+ oils are made with the same process as Group III 'unconventional motor oils', do you think that Group II/II+ oils' are less reliant on polymer's than Group I oils'?
Scott
It's my understanding that synthetic's contain less 'fractions' than conventional motor oils' and contain their viscosity over a much wider temperature range. So they are less dependant or perhaps need no assistance at all from polymer's to stay in viscosity grade.
You probably know where I'm going with this...
What I'd like to know is since we now know that Group II and II+ oils are made with the same process as Group III 'unconventional motor oils', do you think that Group II/II+ oils' are less reliant on polymer's than Group I oils'?
Scott
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Viscosity- what does it mean?
Scott,
I am working on a post that will cover the properties of each group, how they are manufactured, benefits and disadvantages of each but I am leaving and won't have time to finish it til I get back. See ya 2 weeks.
I am working on a post that will cover the properties of each group, how they are manufactured, benefits and disadvantages of each but I am leaving and won't have time to finish it til I get back. See ya 2 weeks.
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Viscosity- what does it mean?
Flash,
I will be looking forward to your follow up message, but in the meantime you lost me with your response to Rockledge's question #3. If you could idealize an environment in which you always drive and store your vehicle at an ambient temp of 70F, what would be the point (benefit) of using anything other than a straight weight oil? Would the benefits come from the change in internal engine temperature only?
I am referring to a purely theoretical case which doesn't represent reality, but I am hoping to gain understanding from this example. Thanks.
I will be looking forward to your follow up message, but in the meantime you lost me with your response to Rockledge's question #3. If you could idealize an environment in which you always drive and store your vehicle at an ambient temp of 70F, what would be the point (benefit) of using anything other than a straight weight oil? Would the benefits come from the change in internal engine temperature only?
I am referring to a purely theoretical case which doesn't represent reality, but I am hoping to gain understanding from this example. Thanks.
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Viscosity- what does it mean?
brg_ranger, If I understand the hypothisis correctly, we have an environment that is a constant 70F, would there be an advantage to a multi-weight? Most likely no. At 70F straight weight oil wouldn't have any flow problems and there wouldn't be much use for VII's. Also, wouldn't be any demand for a synthetic based oil either. Unfortunately, we don't live in that environment. When I was a kid, we always used a 30W oil in the cars, trucks, and tractors. When it got cold/below freezing, nobody give cold start up any attention. The engines started, ran tight for awhile and then you drove off. We also had to overhaul most of the motors at about 75,000 miles. I can even remember that the Pennsylvania oil was the best, there were no grades like SL or CH-4. I even remember that my grandad and me entered and ran in the Mobil Oil Economy Run, how times have changed.
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