Originally Posted By: MarkStock
Originally Posted By: OVERK1LL
Operating conditions, as I mentioned earlier, are different in Europe. At 150Mph on the Autobahn, my oil temp is going to be a heck of a lot higher than yours putting around on i-whatever at 70mph.
Believe it or not, the engineers who design these engines actually test them under a variety of operating conditions and then spec them for a lubricant (or lubricants) that will provide adequate protection under those conditions. They don't just slap on oil pressure and oil temperature gauges and go to town. They do controlled testing with tear-downs to determine what works and what doesn't. Some of these tests are extreme (Ford's Ecoboost test, the Porsche Nurburgring test....etc) but their purpose is to try and break things so that they can figure out how to make it so that things don't break under that usage profile.
Power density is a key component of what defines and engine's oil temperature operating range. Higher power density engines will heat the oil further. Often a combination of increased sump capacity, oil coolers and heavier oils are used to deal with this phenomena.
And every one of these things has a drawback.
-Heavier oil causes increased drag while heating up and can cause an engine to be sluggish
-Oil coolers, if not thermostatically controlled, will cause the oil to take longer to heat and thin, prolonging the time the lubricant is excessively heavy for the application
-Increased sump size again increases the amount of time taken for the lubricant to warm up, but it also acts as a heat sink and a larger sump allows for a thinner lubricant to be used, all things considered, as it will keep overall oil temperature lower.
This is also why oils like GC, M1 0w40....etc exist. They are relatively "heavy" with their higher HTHS values, but offer exceptional cold temperature performance compared to the 5w40, 10w40 and 15w40 lubricants they displaced.
Ford's sheer-happy 5w50 is another example of an oil designed to perform in a similar manner. Heavy enough to provide adequate protection for the BOSS 302 and Shelby engines under track-use conditions, whilst still being thin enough to function properly in daily driver use.
What you say about autobahn kind of makes sense, but my Mercedes manual talks about choosing oil based on the lowest ambient air temperature, not the maximum highway speed.
And as far as I know, the MB229.5 spec is worldwide.
On another note, it does say lowest ambient air temp. It's interesting that the bars for 30 weight oil max out at 86f. If I were to interpret the chart as a range for both lower and upper temp, even though the text says to choose based on lowest ambient air temp, it would say I couldn't run GC 0w30 in many parts of the US in summer.
Yes, because the ambient air temperature plays a key role in how hot the oil gets.
For example, now that it is cold out, I can't get my oil any hotter than 75 degrees or so in the exact same driving profile that was heating the oil to around 90 degrees only a month ago.
Same usage profile, simply the ambient temperature works to drive oil temperatures down.
Now, the touching on the MB oil spec is also key here, as it, similar to the BMW spec's, means that an oil meets a minimum level of performance as well as a number criteria required for the application like HTHS.
So basically, as long as you use an oil certified for the application, you are covered, as it is guaranteed to meet the minimum performance requirements required to protect the engine under various operating conditions. So be it 0w30, 0w40, 5w40...etc, as long as it has the MB seal on it, you are good