When you get down to the space that the oil fills between, say a crankshaft and the bearing shell where the shaft is riding on a wedge of oil as it spins, how much difference does the viscosity make in an engine at operating temperature? For which part of a modern gasoline engine should the viscosity be optimized. Should you first look out for the cylinder walls, the big end bearings, the valve gear or valve guides? Or are modern oils so good it makes no difference, you just go as thin as you dare?
Effective oil viscosity
- Thread starter OneEyeJack
- Start date
- Status
what engine and make of car?
Originally Posted By: OneEyeJack
When you get down to the space that the oil fills between, say a crankshaft and the bearing shell where the shaft is riding on a wedge of oil as it spins, how much difference does the viscosity make in an engine at operating temperature? For which part of a modern gasoline engine should the viscosity be optimized. Should you first look out for the cylinder walls, the big end bearings, the valve gear or valve guides? Or are modern oils so good it makes no difference, you just go as thin as you dare?
I believe so, that why I'm running synthetic xW20 in '00 E430 spec'd M1 0W40. The engine is much quieter with thinner oil and I get better gas mileage as well. My butt dyno telling me it accelerates quicker with thinner oil too.
When you get down to the space that the oil fills between, say a crankshaft and the bearing shell where the shaft is riding on a wedge of oil as it spins, how much difference does the viscosity make in an engine at operating temperature? For which part of a modern gasoline engine should the viscosity be optimized. Should you first look out for the cylinder walls, the big end bearings, the valve gear or valve guides? Or are modern oils so good it makes no difference, you just go as thin as you dare?
I believe so, that why I'm running synthetic xW20 in '00 E430 spec'd M1 0W40. The engine is much quieter with thinner oil and I get better gas mileage as well. My butt dyno telling me it accelerates quicker with thinner oil too.
- Joined
- Sep 28, 2002
- Messages
- 39,798
Quote:
Or are modern oils so good it makes no difference, you just go as thin as you dare?
To quote ..maybe paraphrase...one of our senior mods ..who's also an engineer and actually designed journal bearings at one point in his esteemed career:
The successful use of thinner oils is more a testimony to the robust nature of engine design than it is the properties of the oil.
Modern engines, most of them anyway, end runaround stuff with rollerized cam followers ..and I haven't heard of an engine seizure in a long time...
That all said, there will be a minimum HTHS spec set by the OEM.
Or are modern oils so good it makes no difference, you just go as thin as you dare?
To quote ..maybe paraphrase...one of our senior mods ..who's also an engineer and actually designed journal bearings at one point in his esteemed career:
The successful use of thinner oils is more a testimony to the robust nature of engine design than it is the properties of the oil.
Modern engines, most of them anyway, end runaround stuff with rollerized cam followers ..and I haven't heard of an engine seizure in a long time...
That all said, there will be a minimum HTHS spec set by the OEM.
Originally Posted By: OneEyeJack
When you get down to the space that the oil fills between, say a crankshaft and the bearing shell where the shaft is riding on a wedge of oil as it spins, how much difference does the viscosity make in an engine at operating temperature?
It can make a big difference. At a bare minimum, you need oil pressure, which requires viscosity.
Originally Posted By: OneEyeJack
For which part of a modern gasoline engine should the viscosity be optimized. Should you first look out for the cylinder walls, the big end bearings, the valve gear or valve guides?
All of it, technically...
Originally Posted By: OneEyeJack
Or are modern oils so good it makes no difference, you just go as thin as you dare?
As thin as possible, as thick as necessary.
Modern oils might have higher viscosity indices, which would allow them to retain their viscosity better in some of the hottest areas. Just to make up an example: A modern SAE 30 might have comparable viscosity to an SAE 40 from yesteryear in, say, your top piston rings (although it would probably be thicker just about everywhere else), because the heat doesn't thin out the modern 30 as much as it thins out the old school 40. So, if your top piston rings are the main limiting factor on how thin you can go, it's possible that a modern oil could allow you to run a lower viscosity grade than an older oil could.
When you get down to the space that the oil fills between, say a crankshaft and the bearing shell where the shaft is riding on a wedge of oil as it spins, how much difference does the viscosity make in an engine at operating temperature?
It can make a big difference. At a bare minimum, you need oil pressure, which requires viscosity.
Originally Posted By: OneEyeJack
For which part of a modern gasoline engine should the viscosity be optimized. Should you first look out for the cylinder walls, the big end bearings, the valve gear or valve guides?
All of it, technically...
Originally Posted By: OneEyeJack
Or are modern oils so good it makes no difference, you just go as thin as you dare?
As thin as possible, as thick as necessary.
Modern oils might have higher viscosity indices, which would allow them to retain their viscosity better in some of the hottest areas. Just to make up an example: A modern SAE 30 might have comparable viscosity to an SAE 40 from yesteryear in, say, your top piston rings (although it would probably be thicker just about everywhere else), because the heat doesn't thin out the modern 30 as much as it thins out the old school 40. So, if your top piston rings are the main limiting factor on how thin you can go, it's possible that a modern oil could allow you to run a lower viscosity grade than an older oil could.
Quote:
Modern oils might have higher viscosity indices, which would allow them to retain their viscosity better in some of the hottest areas. Just to make up an example: A modern SAE 30 might have comparable viscosity to an SAE 40 from yesteryear in, say, your top piston rings (although it would probably be thicker just about everywhere else), because the heat doesn't thin out the modern 30 as much as it thins out the old school 40. So, if your top piston rings are the main limiting factor on how thin you can go, it's possible that a modern oil could allow you to run a lower viscosity grade than an older oil could.
+1
Though i use the Oil Pressure gauge in my car to tell me what oil is "flowing" the best (Not giving highest pressure, as most do) i can tell you that a 40 has same OP as a 50. (xW-40, say 10W-40, same as 20W-50.. same brand.)
Why? Because the 10W-40 is THAT THICK. Is that good? .. Sure. But I, and this is specific for me, need a THIN 40 to get Optimal pressure, and that = Flow, and that = Lubrication.. the other oil, though "Better," MIGHT NOT have been Lubricating at higher OP. Maybe was. Maybe wasnt. I like to be sure(r.)
Hope this helps.
(btw, Oil pressure should be not "Sky high" but the Oil light shouldnt be coming on either. Most modern FI engines, 40PSi to 60Psi fully warmed up is fine.)
Modern oils might have higher viscosity indices, which would allow them to retain their viscosity better in some of the hottest areas. Just to make up an example: A modern SAE 30 might have comparable viscosity to an SAE 40 from yesteryear in, say, your top piston rings (although it would probably be thicker just about everywhere else), because the heat doesn't thin out the modern 30 as much as it thins out the old school 40. So, if your top piston rings are the main limiting factor on how thin you can go, it's possible that a modern oil could allow you to run a lower viscosity grade than an older oil could.
+1
Though i use the Oil Pressure gauge in my car to tell me what oil is "flowing" the best (Not giving highest pressure, as most do) i can tell you that a 40 has same OP as a 50. (xW-40, say 10W-40, same as 20W-50.. same brand.)
Why? Because the 10W-40 is THAT THICK. Is that good? .. Sure. But I, and this is specific for me, need a THIN 40 to get Optimal pressure, and that = Flow, and that = Lubrication.. the other oil, though "Better," MIGHT NOT have been Lubricating at higher OP. Maybe was. Maybe wasnt. I like to be sure(r.)
Hope this helps.
(btw, Oil pressure should be not "Sky high" but the Oil light shouldnt be coming on either. Most modern FI engines, 40PSi to 60Psi fully warmed up is fine.)
Higher oil pressure that is achieved by higher viscosity will never result in more flowing oil - at least not at the pump. The pressure is higher with increased viscosity due to the resistance to flow. There may by a point where an oil is so thin that the flow does not make it to the top end but I do not know of such a case.
If there is no leakage within the pump and the bypass is not engaged, then the flow is identical at any pressure at fixed RPMs. However, as the pressure is increased the there will be more leakage within the pump and a great likelihood that the bypass will begin to release.
If there is no leakage within the pump and the bypass is not engaged, then the flow is identical at any pressure at fixed RPMs. However, as the pressure is increased the there will be more leakage within the pump and a great likelihood that the bypass will begin to release.
Originally Posted By: GMorg
Higher oil pressure that is achieved by higher viscosity will never result in more flowing oil - at least not at the pump. The pressure is higher with increased viscosity due to the resistance to flow. There may by a point where an oil is so thin that the flow does not make it to the top end but I do not know of such a case.
If there is no leakage within the pump and the bypass is not engaged, then the flow is identical at any pressure at fixed RPMs. However, as the pressure is increased the there will be more leakage within the pump and a great likelihood that the bypass will begin to release.
+1
The oil pressure gauge one may have installed actually measures the back pressure in the system. Consiquently the lower the oil pressure reading the lower the oil's viscosity and the higher the oil flow.
The trick to optimizing the oil viscosity for any engine application is to choose the lightest oil that still provides the minimum oil pressure spec'd for the engine when the oil is as hot as it will ever get.
Higher oil pressure that is achieved by higher viscosity will never result in more flowing oil - at least not at the pump. The pressure is higher with increased viscosity due to the resistance to flow. There may by a point where an oil is so thin that the flow does not make it to the top end but I do not know of such a case.
If there is no leakage within the pump and the bypass is not engaged, then the flow is identical at any pressure at fixed RPMs. However, as the pressure is increased the there will be more leakage within the pump and a great likelihood that the bypass will begin to release.
+1
The oil pressure gauge one may have installed actually measures the back pressure in the system. Consiquently the lower the oil pressure reading the lower the oil's viscosity and the higher the oil flow.
The trick to optimizing the oil viscosity for any engine application is to choose the lightest oil that still provides the minimum oil pressure spec'd for the engine when the oil is as hot as it will ever get.
In a properly operating automotive engine the rings are what limits the life of an engine before a rebuild is necessary.
Originally Posted By: AEHaas
In a properly operating automotive engine the rings are what limits the life of an engine before a rebuild is necessary.
To get to the Rings, Head needs removed, right?
I was tempted to try a nice long A-Rx treatment to see what it did for my rings. That, and Injectors, as well as Coil, were suspect.
In a properly operating automotive engine the rings are what limits the life of an engine before a rebuild is necessary.
To get to the Rings, Head needs removed, right?
I was tempted to try a nice long A-Rx treatment to see what it did for my rings. That, and Injectors, as well as Coil, were suspect.
Hi,
AEHaas - You said this;
"In a properly operating automotive engine the rings are what limits the life of an engine before a rebuild is necessary."
This statement is a Theory - in practice there are other factors!
AEHaas - You said this;
"In a properly operating automotive engine the rings are what limits the life of an engine before a rebuild is necessary."
This statement is a Theory - in practice there are other factors!
Originally Posted By: Doug Hillary
Hi,
AEHaas - You said this;
"In a properly operating automotive engine the rings are what limits the life of an engine before a rebuild is necessary."
This statement is a Theory - in practice there are other factors!
Thats all Dr. Haas has. Thats why he puts 0W-20 in his exotic supercars!
Hi,
AEHaas - You said this;
"In a properly operating automotive engine the rings are what limits the life of an engine before a rebuild is necessary."
This statement is a Theory - in practice there are other factors!
Thats all Dr. Haas has. Thats why he puts 0W-20 in his exotic supercars!
Originally Posted By: HangerHarley
Thats all Dr. Haas has. Thats why he puts 0W-20 in his exotic supercars!
Dr. Haas's choices don't come out of thin air. They are backed up by a fair amount of testing. He may be wrong on some of the theoretical stuff, and of course I would never take his word over Doug's, but it's unfair to suggest that he just pulls stuff out of his rear.
Thats all Dr. Haas has. Thats why he puts 0W-20 in his exotic supercars!
Dr. Haas's choices don't come out of thin air. They are backed up by a fair amount of testing. He may be wrong on some of the theoretical stuff, and of course I would never take his word over Doug's, but it's unfair to suggest that he just pulls stuff out of his rear.
Hi,
dOOdfOOd - Your comments are correct
dOOdfOOd - Your comments are correct
An oil pressure reading might depend a bit on where you take your reading and what the oil pressure relief valve is doing.
The comment about the rings might be tempered with that fact that an engine might need a valve job, valve guide seals or a head gasket long before the rings or bearings or other parts of an engine ever need attention. I had a 78 Toyota pickup that has gone through head work three times so far and the rings and bottom end have never been touched. It's still running and on it's third owner now, a neighbor, and the darn thing refuses to quit. It's never seen synthetic oil or been pampered. It starts right up and runs great and it looks like the bottom end might just last forever. The problem is that the body is going to fall apart long before the engine dies. The oil is what ever 5w-30 is on sale. It gets changed every 3-4k miles.
The comment about the rings might be tempered with that fact that an engine might need a valve job, valve guide seals or a head gasket long before the rings or bearings or other parts of an engine ever need attention. I had a 78 Toyota pickup that has gone through head work three times so far and the rings and bottom end have never been touched. It's still running and on it's third owner now, a neighbor, and the darn thing refuses to quit. It's never seen synthetic oil or been pampered. It starts right up and runs great and it looks like the bottom end might just last forever. The problem is that the body is going to fall apart long before the engine dies. The oil is what ever 5w-30 is on sale. It gets changed every 3-4k miles.
Originally Posted By: OneEyeJack
An oil pressure reading might depend a bit on where you take your reading and what the oil pressure relief valve is doing.
Not really.
One should always, if they can, operate an engine below the point at which the oil pump relief valve is activated. That means keeping the rev's down when warming up a cold engine. When the oil is up to normal operating temp's you should be able to rev the engin to red line, and thereby raising the oil pressure to it's maximum, without activating the relief valve and their should be room to spare. If you can't you're running too heavy an oil.
The spec' OP for an engine is of course always below the relief valve setting.
An oil pressure reading might depend a bit on where you take your reading and what the oil pressure relief valve is doing.
Not really.
One should always, if they can, operate an engine below the point at which the oil pump relief valve is activated. That means keeping the rev's down when warming up a cold engine. When the oil is up to normal operating temp's you should be able to rev the engin to red line, and thereby raising the oil pressure to it's maximum, without activating the relief valve and their should be room to spare. If you can't you're running too heavy an oil.
The spec' OP for an engine is of course always below the relief valve setting.
Originally Posted By: CATERHAM
Originally Posted By: OneEyeJack
An oil pressure reading might depend a bit on where you take your reading and what the oil pressure relief valve is doing.
Not really.
One should always, if they can, operate an engine below the point at which the oil pump relief valve is activated. That means keeping the rev's down when warming up a cold engine. When the oil is up to normal operating temp's you should be able to rev the engin to red line, and thereby raising the oil pressure to it's maximum, without activating the relief valve and their should be room to spare. If you can't you're running too heavy an oil.
The spec' OP for an engine is of course always below the relief valve setting.
Youd think that.. but some cars make me wonder.
CATERHAM you have inspired me to go with a 10W-40 on my car. And a certain brand at that i suspect it is a "Thin 40." It is the only one out of three different brands and grades (and one brand i tried two grades to compare and see) that gives me "Below relief" when operating driving down the road, not just "At idle" fully warmed.
I believe a car's Oil Pressure gauge, even a dampered one, gives an indication of what is happening, and should be trusted.
Now if only there was a way to tell when the oil is shearing.
Originally Posted By: OneEyeJack
An oil pressure reading might depend a bit on where you take your reading and what the oil pressure relief valve is doing.
Not really.
One should always, if they can, operate an engine below the point at which the oil pump relief valve is activated. That means keeping the rev's down when warming up a cold engine. When the oil is up to normal operating temp's you should be able to rev the engin to red line, and thereby raising the oil pressure to it's maximum, without activating the relief valve and their should be room to spare. If you can't you're running too heavy an oil.
The spec' OP for an engine is of course always below the relief valve setting.
Youd think that.. but some cars make me wonder.
CATERHAM you have inspired me to go with a 10W-40 on my car. And a certain brand at that i suspect it is a "Thin 40." It is the only one out of three different brands and grades (and one brand i tried two grades to compare and see) that gives me "Below relief" when operating driving down the road, not just "At idle" fully warmed.
I believe a car's Oil Pressure gauge, even a dampered one, gives an indication of what is happening, and should be trusted.
Now if only there was a way to tell when the oil is shearing.
Originally Posted By: d00df00d
Originally Posted By: HangerHarley
Thats all Dr. Haas has. Thats why he puts 0W-20 in his exotic supercars!
Dr. Haas's choices don't come out of thin air. They are backed up by a fair amount of testing. He may be wrong on some of the theoretical stuff, and of course I would never take his word over Doug's, but it's unfair to suggest that he just pulls stuff out of his rear.
Ill go with Doug. Dr. Haas has a lot of testing, and who knows how his engines look. Id stick with OP recommendations, not go trying to put the thinnest stuff in the world in cars just to do it. Sounds like he has nothing else to do but chance expensive cars that he can because he has money. Im simply not all as impressed with his pages, and pages.. and pages that basically say "Put the thinnest stuff in you can find." and yes, i read it. (If the car manufacturer of that $600,000+ Enzo wanted 10W-30 in a car that says Put 10W-60 in it they would say so, not leave you, the new owner, to guess and go monkeying around in the oil system. Lambo maybe coulda went with a better BRAND than AGIP but thats a 6.2L V-12.. Sorry.)
Doug: Your comments are correct. You trump Haas, whether his comments come from his rear or his front. More power to ya.
d00df00d that means that you are correct too, sinee i said Doug Hillary is correct, and then praised him directly...
Originally Posted By: HangerHarley
Thats all Dr. Haas has. Thats why he puts 0W-20 in his exotic supercars!
Dr. Haas's choices don't come out of thin air. They are backed up by a fair amount of testing. He may be wrong on some of the theoretical stuff, and of course I would never take his word over Doug's, but it's unfair to suggest that he just pulls stuff out of his rear.
Ill go with Doug. Dr. Haas has a lot of testing, and who knows how his engines look. Id stick with OP recommendations, not go trying to put the thinnest stuff in the world in cars just to do it. Sounds like he has nothing else to do but chance expensive cars that he can because he has money. Im simply not all as impressed with his pages, and pages.. and pages that basically say "Put the thinnest stuff in you can find." and yes, i read it. (If the car manufacturer of that $600,000+ Enzo wanted 10W-30 in a car that says Put 10W-60 in it they would say so, not leave you, the new owner, to guess and go monkeying around in the oil system. Lambo maybe coulda went with a better BRAND than AGIP but thats a 6.2L V-12.. Sorry.)
Doug: Your comments are correct. You trump Haas, whether his comments come from his rear or his front. More power to ya.
d00df00d that means that you are correct too, sinee i said Doug Hillary is correct, and then praised him directly...
Harley, you asked?
Now if only there was a way to tell when the oil is shearing.[/quote]
That's one of the advantages of having an OP gauge in your car but to accurately measure viscosity loss it helps to have an oil temp gauge as well. With both gauges you take the OP readings at a couple of oil temps when the oil is fresh.
As you rack up the miles, if the OP drops at the same oil temp readings then you've got viscosity loss which can be due to shearing and/or fuel dilution.
Dr. Haas has both OP and oil temp gauges in his flash cars.
He knows exactly what he is doing and is taking zero risk in running lighter than spec' oil since he is always maintaining adequate oil pressure and therefore the operational viscosity in his various engines is always atleast somewhat higher than necessary.
How does he manage it? Simple, here in NA it's virtually impossible to drive his high performance cars fast enough for long enough for his oil temp's to get high enough to warrant the heavier spec' oil. And that applies to pretty much everyone with a high performance car who doesn't take their car to the track.
Now if only there was a way to tell when the oil is shearing.[/quote]
That's one of the advantages of having an OP gauge in your car but to accurately measure viscosity loss it helps to have an oil temp gauge as well. With both gauges you take the OP readings at a couple of oil temps when the oil is fresh.
As you rack up the miles, if the OP drops at the same oil temp readings then you've got viscosity loss which can be due to shearing and/or fuel dilution.
Dr. Haas has both OP and oil temp gauges in his flash cars.
He knows exactly what he is doing and is taking zero risk in running lighter than spec' oil since he is always maintaining adequate oil pressure and therefore the operational viscosity in his various engines is always atleast somewhat higher than necessary.
How does he manage it? Simple, here in NA it's virtually impossible to drive his high performance cars fast enough for long enough for his oil temp's to get high enough to warrant the heavier spec' oil. And that applies to pretty much everyone with a high performance car who doesn't take their car to the track.
And one other thing, Dr. Haas doesn't run "the thinnest stuff [oil] you can find" in his high performance cars.
In fact he's never run an oil in his cars with a HTHS vis' even as low as 2.9cP, the entry point for a SAE 30wt.
So 99.99% of us users of OTC 20wt oil are running significantly lighter oil (myself included) than what Dr. Haas would dream of putting in his cars.
In fact he's never run an oil in his cars with a HTHS vis' even as low as 2.9cP, the entry point for a SAE 30wt.
So 99.99% of us users of OTC 20wt oil are running significantly lighter oil (myself included) than what Dr. Haas would dream of putting in his cars.
- Status
Similar threads
