I will use 5w-40 for the first time this summer because of the Rotella rebate. But i generally run Amsoil 15w-40.
If the prices were the same, I always opt for the oil with the fewest thickening additives. An oil that has fewer thickening additives is typically a better option for hot weather. IMHO.
15W - 40 flows well enough at my climate's ambient temps.... pretty much year round. One could argue that 5w- 40 will protect better at engine start up even when it is 90+ degrees out because it will flow quicker? *Maybe.
The disadvantage with a wide range viscosity oil like 5w-40 is that the shear forces and higher heat levels of a diesel can cause the thickening agents to decompose. The thickening agents are carbon/nitrogen polymers that when broken into smaller molecules can turn into gum (which can tug at piston rings and the like.)
This can happen with all multiweight oils. But since 5W-40 has more thickening additives than 15W-40, 5w-40 is in my opinion best reserved for when it is needed at lower ambient temps.
The fewer additives you have in your oil to make it thicker, the more protective oil you have per ml *of volume. *The thickening agents aren't slick like the oil is. And the thickening agents will break down faster than the base oil that it is being carried in.
Even if i drove 30,000+ miles per year, i wouldn't run my oil 15,000 miles. Oil analysis will tell you most of the important detials. But will it tell you the characteristics of the particles in your oil? I run 2 filters. The mopar full flow filter and an Amsoil Bypass filter. I hope the gum gets caught in the filter with that extra filtration and the 3 micron insurance of the amsoil.
If the prices were the same, I always opt for the oil with the fewest thickening additives. An oil that has fewer thickening additives is typically a better option for hot weather. IMHO.
15W - 40 flows well enough at my climate's ambient temps.... pretty much year round. One could argue that 5w- 40 will protect better at engine start up even when it is 90+ degrees out because it will flow quicker? *Maybe.
The disadvantage with a wide range viscosity oil like 5w-40 is that the shear forces and higher heat levels of a diesel can cause the thickening agents to decompose. The thickening agents are carbon/nitrogen polymers that when broken into smaller molecules can turn into gum (which can tug at piston rings and the like.)
This can happen with all multiweight oils. But since 5W-40 has more thickening additives than 15W-40, 5w-40 is in my opinion best reserved for when it is needed at lower ambient temps.
The fewer additives you have in your oil to make it thicker, the more protective oil you have per ml *of volume. *The thickening agents aren't slick like the oil is. And the thickening agents will break down faster than the base oil that it is being carried in.
Even if i drove 30,000+ miles per year, i wouldn't run my oil 15,000 miles. Oil analysis will tell you most of the important detials. But will it tell you the characteristics of the particles in your oil? I run 2 filters. The mopar full flow filter and an Amsoil Bypass filter. I hope the gum gets caught in the filter with that extra filtration and the 3 micron insurance of the amsoil.
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