Originally Posted By: Gary Allan
I tend to take the inverted view on the CAFE reference. It's obvious that engines survive just fine in either environment on either diet of higher vs. lower visc. Physics just doesn't take a vacation at the 200 mile limit. Everyone looks at visc in isolation and anoint it with magical properties.
Quite right. If the engine never warms up to operating temperatures, 5w-20 isn't going to "thin out like mad" or anything catastrophic, and wouldn't do so at temperature, either. People have to look at their application and conditions, really. The charts that were, and occasionally still are, in manuals are there for a reason. Many performance cars, particularly those without a U.S./Canadian origin, specify thicker oils for high temperature, high speed sustained driving.
A run at 85 mph for an hour has a far different effect on oil temperatures (and therefore viscosity) than does a two block trip to the grocery store. For someone who engages in a lot of such short trips, I suspect 5w-20 would be perfect. My trips are rarely that short. Winter is more of an issue here, so the first number is crucial. In my Audi, I use 5w-40 or -30 in the winter, or even a 0w-xx in the winter. Even though it's not speced for it, I suspect a 5w-20 or 0w-20 would be fine in the winter, especially if I did a lot of short trips. There is no way, however, that I'd use it in my Audi on a sustained, high speed run in the summer.
There simply is no magical solution. CAFE has its requirements, and testing to meet CAFE doesn't always translate into a perfect choice in real world applications.
I tend to take the inverted view on the CAFE reference. It's obvious that engines survive just fine in either environment on either diet of higher vs. lower visc. Physics just doesn't take a vacation at the 200 mile limit. Everyone looks at visc in isolation and anoint it with magical properties.
Quite right. If the engine never warms up to operating temperatures, 5w-20 isn't going to "thin out like mad" or anything catastrophic, and wouldn't do so at temperature, either. People have to look at their application and conditions, really. The charts that were, and occasionally still are, in manuals are there for a reason. Many performance cars, particularly those without a U.S./Canadian origin, specify thicker oils for high temperature, high speed sustained driving.
A run at 85 mph for an hour has a far different effect on oil temperatures (and therefore viscosity) than does a two block trip to the grocery store. For someone who engages in a lot of such short trips, I suspect 5w-20 would be perfect. My trips are rarely that short. Winter is more of an issue here, so the first number is crucial. In my Audi, I use 5w-40 or -30 in the winter, or even a 0w-xx in the winter. Even though it's not speced for it, I suspect a 5w-20 or 0w-20 would be fine in the winter, especially if I did a lot of short trips. There is no way, however, that I'd use it in my Audi on a sustained, high speed run in the summer.
There simply is no magical solution. CAFE has its requirements, and testing to meet CAFE doesn't always translate into a perfect choice in real world applications.
