Originally Posted By: e55amgbenz007
Originally Posted By: Gokhan
Originally Posted By: Jaymie
Interesting, is that because it won’t flow as quickly?
No, thicker motor oil runs hotter because higher HTHS viscosity (HTHSV) causes more friction in the bearings. That is why the fuel economy drops with the increasing HTHSV.
From your oil temperatures (convert them to C first so that they would be useful) -- 102 C without towing and 112 C with towing -- definitely go with 5W-30 for towing. It would give an extra margin of safety for towing. There is probably no need for 0W-40 unless you want to do extreme towing.
You can play around with the Widman calculator for the operational viscosity. Just plug in the KV40 and KV100 values from the data sheets.
https://www.widman.biz/English/Calculators/Operational.html
That doesn't take into account the need for higher viscosity (particularly HTHSV) because of more load in the bearings but at least it takes into account the oil temperature.
Here is the fundamental curve of lubrication -- Stribeck curve -- that tells you what happens when you change the HTHSV (n [eta]), load (P), and RPM (v). In the bearings you want to stay in the hydrodynamic-lubrication region:
Wait, I am lost here. Engines, such as the European variety that require a higher HTHS film strength are actually increasing the friction/wear with the requirement?
There are at least two contributions to friction here. The first is the boundary friction, which is the friction that happens when the two surfaces directly make contact. This happens in the boundary-lubrication region. The second is the the viscous friction, which is the oil's internal friction. This happens in the hydrodynamic-lubrication region. Boundary friction causes wear but the viscous friction does not. In the hydrodynamic-lubrication region, there is a thick oil film separating the surfaces. Viscous friction increases with the thickness of the oil film but does not cause wear as long as the minimum oil-film thickness (MOFT) is greater than the surface roughness and/or contaminant-particle size. So, fuel economy drops as you move further right on the Stribeck curve but the oil-film thickness increases and the margin of safety against oil-film collapse or against abrasive wear by surface roughness or contaminant particles in the bearings increases.
Originally Posted By: Gokhan
Originally Posted By: Jaymie
Interesting, is that because it won’t flow as quickly?
No, thicker motor oil runs hotter because higher HTHS viscosity (HTHSV) causes more friction in the bearings. That is why the fuel economy drops with the increasing HTHSV.
From your oil temperatures (convert them to C first so that they would be useful) -- 102 C without towing and 112 C with towing -- definitely go with 5W-30 for towing. It would give an extra margin of safety for towing. There is probably no need for 0W-40 unless you want to do extreme towing.
You can play around with the Widman calculator for the operational viscosity. Just plug in the KV40 and KV100 values from the data sheets.
https://www.widman.biz/English/Calculators/Operational.html
That doesn't take into account the need for higher viscosity (particularly HTHSV) because of more load in the bearings but at least it takes into account the oil temperature.
Here is the fundamental curve of lubrication -- Stribeck curve -- that tells you what happens when you change the HTHSV (n [eta]), load (P), and RPM (v). In the bearings you want to stay in the hydrodynamic-lubrication region:
Wait, I am lost here. Engines, such as the European variety that require a higher HTHS film strength are actually increasing the friction/wear with the requirement?
There are at least two contributions to friction here. The first is the boundary friction, which is the friction that happens when the two surfaces directly make contact. This happens in the boundary-lubrication region. The second is the the viscous friction, which is the oil's internal friction. This happens in the hydrodynamic-lubrication region. Boundary friction causes wear but the viscous friction does not. In the hydrodynamic-lubrication region, there is a thick oil film separating the surfaces. Viscous friction increases with the thickness of the oil film but does not cause wear as long as the minimum oil-film thickness (MOFT) is greater than the surface roughness and/or contaminant-particle size. So, fuel economy drops as you move further right on the Stribeck curve but the oil-film thickness increases and the margin of safety against oil-film collapse or against abrasive wear by surface roughness or contaminant particles in the bearings increases.