Hi Friends,
This is not another "Which is better, thin or thick oil?" thread. As there are tons of discussions about it in this forum
But i am a little confused, because Shell's research has different results compared with other researches. (Likely i have missed the point.)
Shell Research:
Quote:
The assumption that lower viscosity lubricants automatically give rise to thinner oil films in
key lubricated contacts in a gasoline engine is also open to question, particularly in the case
of piston rings. Laser Induced Fluorescence measurements have found that, in a Nissan
gasoline engine, the mid-stroke top ring oil film thickness was greater for an SAE-5W/20
lubricant than it was for an SAE-15W/40 lubricant. These effects were also observed in our
laboratory for monograde lubricants. Similar effects have been observed by S.L. Moore of
BP36. Figure 20 illustrates the observations. A qualitative explanation of such an effect
could be as follows : There are two routes by which lubricant reaches the top piston ring.
Route #1 (the “conventional” route) is that oil is left on the liner by the passage of the
preceding ring. The higher the oil viscosity, the larger will be the oil film thickness left on
the liner. Route #2 involves oil being transported to the top piston ring via the ring gaps
(such flows have been observed by Nakashima et al37), and this is thought to favour lower
viscosity lubricants. The precise balance between oil transported by the two routes will
determine whether the oil film thickness under the top ring is greater for a lower viscosity
oil or not.
However, another research shows that OFT is higher with 20w40 than 10w40
Quote:
Comparison of the performance of both SAE
10W40 and SAE 20W40, showed that the increase of
frictional power losses and oil film thickness in case of
SAE 20W40 was strongly related to its high viscosity
compared with SAE 10W40. The high viscosity of the
SAE 20W40 was substantially responsible for the
increase in shear stress in oil film, and could be a
strong reason for the increase in hydrodynamic friction
with the use of the SAE 20W40 oil.
Another research:
Quote:
The oils were compared with each other at different loads and speeds as depicted in
Figure 4.29 and Figure 4.30. Oils 026A, 001C, 004B and 001A which have similar
viscosity give similar OFT and oil AW004 which has the lowest viscosity of all oils
shows a smaller OFT, as expected. On the other hand, oil 097A has the highest OFT as
it has the highest viscosity.
Source:
https://priuschat.com/attachments/fuel-efficient-motor-oil-technical-article-pdf.11772/
https://www.researchgate.net/publication...bustion_engines
http://openaccess.city.ac.uk/11916/1/Oil Transport in Piston Ring Assemblies.pdf
This is not another "Which is better, thin or thick oil?" thread. As there are tons of discussions about it in this forum
But i am a little confused, because Shell's research has different results compared with other researches. (Likely i have missed the point.)
Shell Research:
Quote:
The assumption that lower viscosity lubricants automatically give rise to thinner oil films in
key lubricated contacts in a gasoline engine is also open to question, particularly in the case
of piston rings. Laser Induced Fluorescence measurements have found that, in a Nissan
gasoline engine, the mid-stroke top ring oil film thickness was greater for an SAE-5W/20
lubricant than it was for an SAE-15W/40 lubricant. These effects were also observed in our
laboratory for monograde lubricants. Similar effects have been observed by S.L. Moore of
BP36. Figure 20 illustrates the observations. A qualitative explanation of such an effect
could be as follows : There are two routes by which lubricant reaches the top piston ring.
Route #1 (the “conventional” route) is that oil is left on the liner by the passage of the
preceding ring. The higher the oil viscosity, the larger will be the oil film thickness left on
the liner. Route #2 involves oil being transported to the top piston ring via the ring gaps
(such flows have been observed by Nakashima et al37), and this is thought to favour lower
viscosity lubricants. The precise balance between oil transported by the two routes will
determine whether the oil film thickness under the top ring is greater for a lower viscosity
oil or not.
However, another research shows that OFT is higher with 20w40 than 10w40
Quote:
Comparison of the performance of both SAE
10W40 and SAE 20W40, showed that the increase of
frictional power losses and oil film thickness in case of
SAE 20W40 was strongly related to its high viscosity
compared with SAE 10W40. The high viscosity of the
SAE 20W40 was substantially responsible for the
increase in shear stress in oil film, and could be a
strong reason for the increase in hydrodynamic friction
with the use of the SAE 20W40 oil.
Another research:
Quote:
The oils were compared with each other at different loads and speeds as depicted in
Figure 4.29 and Figure 4.30. Oils 026A, 001C, 004B and 001A which have similar
viscosity give similar OFT and oil AW004 which has the lowest viscosity of all oils
shows a smaller OFT, as expected. On the other hand, oil 097A has the highest OFT as
it has the highest viscosity.
Source:
https://priuschat.com/attachments/fuel-efficient-motor-oil-technical-article-pdf.11772/
https://www.researchgate.net/publication...bustion_engines
http://openaccess.city.ac.uk/11916/1/Oil Transport in Piston Ring Assemblies.pdf