JHZR2
Staff member
Hi,
Today I was thinking about it a bit, and I kind of came up with a new idea...
Oil analysis isnt new, nor are rheological measurements. Therefore, it must have been a well known fact for some time that oils will often shear down to lower viscosities when the get ~3000 miles on them, sometimes before.
5w-30 oils havebeen used for a while (Im using them as an example because it seems that they especially like to shear down to 20 oils).
I believe that manufacturers know full well that oils will shear down, and therefore design the tolerances of engines to be able to be optimally lubricated with an oil of ~5w-20.
I base this on a number fo facts:
-Tolerances in engines have not changed in many years
-Ford went from reccomending 5w-30 to 5w-20 without changing engine design, BUT made a new specification with extended tests to make sure the thinner oil could stand up and protect over longer times (a 20wt will work, buta 10wt is too thin, so it must stay in 20 grade for longer times, whereas a 30 grade can thin out and be OK)
-My BMW reccomends 40 & 50 wt oils in the summer and most of the time, and 30 wt oils when below 40F. At operating temp, all these oils should be the same temperature inside the engine, and so it is logical to say that since they 'ok' a 30 wt oil, it will do just as good of a job protecting as a 50 wt oil at full temp. So the tolerances arent designed for a 40 or 50 wt oil, but really for a 30.
-It seems from UOAs that a lot of oils that have thinned down to ~20, or oils that almost start that way (like M1), still often produce excellent wear numbers, even though they are a lot thinner than the manual suggests)
From these ideas, I would say that my chevy truck (s10 ZR2), which more or less should only use 5w-30, is probably designed for optimal lubrication of an oil that is '20'->~'25' at operating temperature knowing full well that the oil in there will shear down to this viscosity. This would also explain why engines can go hundreds of thousands of miles when oil is changed every 3k, because the viscosity is always just slightly higher than the optimal point. Also, it would explain why it feels to me that vehicles often feel bogged down when using '40' oil compared to a '30', when designed for '30' oil when fully hot... Because it would run best on an oil that is 20ish, and to be up at 40 is too high of a spread, so viscous friction becomes a real issue, posing troubles... To have new oil that is 30 isnt too far away, 40 is just too thick.
OK, so this is real long, I apologize for the length of the post, but this is my idea, and I wanted to get it out so anyone could comment on the potential validity of the idea
Thanks
JMH
[ March 16, 2003, 10:51 PM: Message edited by: JHZR2 ]
Today I was thinking about it a bit, and I kind of came up with a new idea...
Oil analysis isnt new, nor are rheological measurements. Therefore, it must have been a well known fact for some time that oils will often shear down to lower viscosities when the get ~3000 miles on them, sometimes before.
5w-30 oils havebeen used for a while (Im using them as an example because it seems that they especially like to shear down to 20 oils).
I believe that manufacturers know full well that oils will shear down, and therefore design the tolerances of engines to be able to be optimally lubricated with an oil of ~5w-20.
I base this on a number fo facts:
-Tolerances in engines have not changed in many years
-Ford went from reccomending 5w-30 to 5w-20 without changing engine design, BUT made a new specification with extended tests to make sure the thinner oil could stand up and protect over longer times (a 20wt will work, buta 10wt is too thin, so it must stay in 20 grade for longer times, whereas a 30 grade can thin out and be OK)
-My BMW reccomends 40 & 50 wt oils in the summer and most of the time, and 30 wt oils when below 40F. At operating temp, all these oils should be the same temperature inside the engine, and so it is logical to say that since they 'ok' a 30 wt oil, it will do just as good of a job protecting as a 50 wt oil at full temp. So the tolerances arent designed for a 40 or 50 wt oil, but really for a 30.
-It seems from UOAs that a lot of oils that have thinned down to ~20, or oils that almost start that way (like M1), still often produce excellent wear numbers, even though they are a lot thinner than the manual suggests)
From these ideas, I would say that my chevy truck (s10 ZR2), which more or less should only use 5w-30, is probably designed for optimal lubrication of an oil that is '20'->~'25' at operating temperature knowing full well that the oil in there will shear down to this viscosity. This would also explain why engines can go hundreds of thousands of miles when oil is changed every 3k, because the viscosity is always just slightly higher than the optimal point. Also, it would explain why it feels to me that vehicles often feel bogged down when using '40' oil compared to a '30', when designed for '30' oil when fully hot... Because it would run best on an oil that is 20ish, and to be up at 40 is too high of a spread, so viscous friction becomes a real issue, posing troubles... To have new oil that is 30 isnt too far away, 40 is just too thick.
OK, so this is real long, I apologize for the length of the post, but this is my idea, and I wanted to get it out so anyone could comment on the potential validity of the idea
Thanks
JMH
[ March 16, 2003, 10:51 PM: Message edited by: JHZR2 ]
