Originally Posted by Gokhan
Originally Posted by tundraotto
Severe duty with a snot plow is not because of lack of cooling - it's because of the high load on the engine pushing (normally very heavy) snow, continuously.
It's true that you need a thicker oil for low-RPM/high-load operations to maintain the minimum oil-film thickness (MOFT) for hydrodynamic lubrication. However, in footnote 1 the manual doesn't mention 15W-40 for severe-duty service, which is even thicker than 5W-40. They specifically recommend a synthetic oil for severe-duty service.
In any case severe duty is mostly a combination of high oil temperatures and high load, which are related.
High oil temperatures decrease oil life because of faster oxidation.
Severe duty is not limited to high loads and/or high temperatures. Here is the full list:
"Severe" duty conditions include any or any combination of the following:
• Excessive idling
• Frequent short trips in which the engine is shut-down before reaching full operating temperature
• Driving on dusty roads
• Driving off-road or in conditions that require 4 wheel drive
• Frequent towing or hauling (with the exception of very light loads)
• Using biodiesel blends greater than B5 (applies to oil, fuel filters only)
Engine oil
10W-30
Acceptable viscosity in ambient temps > 0° F
Preferred for normal usage
5W-40
Acceptable viscosity in ambient temps > -20° F
Trucks using biodiesel should use 15W-40 or 5W-40
Preferred if truck falls under "Severe Duty" service schedule
15W-40
Acceptable viscosity in ambient temps > 20° F
Trucks using biodiesel should use 15W-40 or 5W-40
0W-30/0W-40
Acceptable viscosity in all ambient temperatures
Recommended in extremely cold conditions only
http://www.powerstrokehub.com/6.7-power-stroke-maintenance.html
While the above is for the 3.0 PowerStroke, the 6.7 specs concerning duty service is similar, although oil specs are by far different.
I'm not buying into the syn vs. conventional argument as to longer OCI. I have a ‘15 6.7 with 125,000 mi. That has had nothing but 10w-30 since it left the Louisville assembly plant. It's my work truck, towing, hauling heavy, running in 90F plus heat during summer months, and short tripping during winter. UOA data doesn't show my regimen of letting the IOLM go to 0% prior to changing oil is detrimental to the health of my truck.
At one point I did have elevated FE, it ended up being attributed to Enerburn fuel additive as when I discontinued its use Fe decreased to roughly 20 ppm at 10,000 mi. OCI.
I also own a 3.0 PowerStroke and plan on running it out until the IOLM goes to 0% also, I guess I'm rogue.