If you are aware of anyone claiming no oil use at high speeds with a 240d. Try using whatever oil they are using. Their multigrade may just be holding better viscosity than whatever you are using. When hot.

Manuals on most of our air cooled lawn tractors specify 10-30 for example. I use straight 30 or 40 weight oil. Some of our engines are really old now and still run as new. We are talking larger lawns. Plus 40 years of use.

You want to reduce oil consumption on a car using 10-30 to about half. Use straight 30 oil. In most cases it will reduce consumption that much.

Many old timers think using 10-30 in an older diesel engine will reduce the lifespan of that engine over time.