I was trying to find some good info on oil and viscosity when I stumbled across this forum.
I was pondering the affects of thicker synthetic oil on our MSP's.
http://www.audiworld.com/tech/eng.html
Very good oil info. (2thumbs)
For example...I was wondering about 15w50?
"Hey I use to think the same way, heavier is better but now know I was wrong. I guess I reached a point of frustration with conflicting and hearsay oil information that I just needed to seek out answers. I have been on this quest for decades and still am. There seem to be two issues that are sighted by the 'heavier oil are better' school of viscosity choice. One is that light oils such as a 0w- will drain away from bearing suffices in warmer weather thus causing wear at start up. The second concern is that a lighter oil such a Mobil 1 0w-30 will not have sufficient 'shear strength' at high temp, high RPM running thus causing oil film breakdown and wear. Both of these views are miss-founded.
If you have not read John Wilkinson's excellent write up on oil viscosity you should, it's right here at Audi World in the technical information section. Perhaps the most compelling reason's John sights (and he sights many) for using a 5W-30 oil is his discussion with engineers from Mobil and Redline. Both men felt that any oil above a 30 weight was not needed for North American operation and both recommended oils such as 5w-30 for the Audi 1.8T motor ( FWI Mobil 1 5w-30 meets or accedes Volkswagen 500.00 and 505.00 oil specs). To quote John "15w-50 oils are a complete waste of power, placing undue (though minor) additional strain on your engine and raising engine temperatures for no real benefit." Not to mention the fact that Audi does not recommend them I might add. I assume if you are reading this, you have been following the oil posts so I will try not to repeat myself too much. Any way, there is an angular velocity of an orbital crankshaft that must plow its way through the oil residing within the plain bearing surface. This moving wave causes mechanical loss and friction, and heavier oil just adds to the loss. So you can see the oil film thickness around the circumference of the 'plane' bearing is not constant. As stated in other posts, you don't want this 'angular velocity' to push through all the oil and result in metal to metal contact and this is where an oils 'shear strength' comes into play. It is true that higher weight oils have more film shear strength but 30 weight has more than enough. If you are looking at oil for "super high performance use" ask yourself if you really need it; do you in fact dive at 145mph for hours at a time? Another quote, this time from a Geiler Corp tech write up "we found that bearings that suffer from irregular lubrication (so called- liquid friction) are working under extremely heavy conditions such as high oil viscosity, high speed, very narrow clearances etc. Routinely have friction coefficients above 0.01". Again lighter weight oils have the following benefits, more power, better gas mileage, better cooling, better lubrication (in most scenarios). And remember a 5w 30 true synthetic oil will have a greater shear strength and resistance of thermal breakdown than a 15w50 conventional oil.
Now to the question of using a 0w-30 motor oil in the summer. I just posted a set of links to FTC cases against oil additive products such as slick 50. One of their many claims that were found to be false was the assertion that there is 'metal on metal ' contact at cold startup with conventional oils. Don't forget that viscosity is NOT a measure of Addison. Oil drains away from engine parts when a motor is at rest. As I said heavy oil drains slower but it sill drains away. As long as the oil will flow (and it will at varying temperatures above -50c) the force of gravity will do it's work. Ester based synthetics, like Amsoil and Mobil 1 have the trait of clinging to metal parts due their polar nature. This means that you will have some lubrication at cold start up regardless of the oil viscosity rating. And as has been pointed out over and over, lighter oil will reach the bearing sooner at start up than heavy oil. Hey if you feel better not using the lighter stuff in the summer, that's ok but there is no reason other than psychological. JIM"
I was pondering the affects of thicker synthetic oil on our MSP's.
http://www.audiworld.com/tech/eng.html
Very good oil info. (2thumbs)
For example...I was wondering about 15w50?
"Hey I use to think the same way, heavier is better but now know I was wrong. I guess I reached a point of frustration with conflicting and hearsay oil information that I just needed to seek out answers. I have been on this quest for decades and still am. There seem to be two issues that are sighted by the 'heavier oil are better' school of viscosity choice. One is that light oils such as a 0w- will drain away from bearing suffices in warmer weather thus causing wear at start up. The second concern is that a lighter oil such a Mobil 1 0w-30 will not have sufficient 'shear strength' at high temp, high RPM running thus causing oil film breakdown and wear. Both of these views are miss-founded.
If you have not read John Wilkinson's excellent write up on oil viscosity you should, it's right here at Audi World in the technical information section. Perhaps the most compelling reason's John sights (and he sights many) for using a 5W-30 oil is his discussion with engineers from Mobil and Redline. Both men felt that any oil above a 30 weight was not needed for North American operation and both recommended oils such as 5w-30 for the Audi 1.8T motor ( FWI Mobil 1 5w-30 meets or accedes Volkswagen 500.00 and 505.00 oil specs). To quote John "15w-50 oils are a complete waste of power, placing undue (though minor) additional strain on your engine and raising engine temperatures for no real benefit." Not to mention the fact that Audi does not recommend them I might add. I assume if you are reading this, you have been following the oil posts so I will try not to repeat myself too much. Any way, there is an angular velocity of an orbital crankshaft that must plow its way through the oil residing within the plain bearing surface. This moving wave causes mechanical loss and friction, and heavier oil just adds to the loss. So you can see the oil film thickness around the circumference of the 'plane' bearing is not constant. As stated in other posts, you don't want this 'angular velocity' to push through all the oil and result in metal to metal contact and this is where an oils 'shear strength' comes into play. It is true that higher weight oils have more film shear strength but 30 weight has more than enough. If you are looking at oil for "super high performance use" ask yourself if you really need it; do you in fact dive at 145mph for hours at a time? Another quote, this time from a Geiler Corp tech write up "we found that bearings that suffer from irregular lubrication (so called- liquid friction) are working under extremely heavy conditions such as high oil viscosity, high speed, very narrow clearances etc. Routinely have friction coefficients above 0.01". Again lighter weight oils have the following benefits, more power, better gas mileage, better cooling, better lubrication (in most scenarios). And remember a 5w 30 true synthetic oil will have a greater shear strength and resistance of thermal breakdown than a 15w50 conventional oil.
Now to the question of using a 0w-30 motor oil in the summer. I just posted a set of links to FTC cases against oil additive products such as slick 50. One of their many claims that were found to be false was the assertion that there is 'metal on metal ' contact at cold startup with conventional oils. Don't forget that viscosity is NOT a measure of Addison. Oil drains away from engine parts when a motor is at rest. As I said heavy oil drains slower but it sill drains away. As long as the oil will flow (and it will at varying temperatures above -50c) the force of gravity will do it's work. Ester based synthetics, like Amsoil and Mobil 1 have the trait of clinging to metal parts due their polar nature. This means that you will have some lubrication at cold start up regardless of the oil viscosity rating. And as has been pointed out over and over, lighter oil will reach the bearing sooner at start up than heavy oil. Hey if you feel better not using the lighter stuff in the summer, that's ok but there is no reason other than psychological. JIM"
