But Arthur, that airflow is so limited compared to taking it off entirely. I've done this several times - the cars consistently run 10 degrees cooler. I've even done on/off, on/off to test the temp. I don't think MB ever said it was there to cool the engine, but to manage the air temps - i.e hotter, for emissions. Add to that the nuissance of it, and the fact that it covers up fluid leaks, it's nuts on an older used car. Volvo used to do it, then just dropped it. I'm still suspicious that it's a ploy to keep customers away from changing their own oil.