When I removed my level sensor to replace the gasket that was leaky I was surprised at how low the oil would have to go before it would "trip". Mine is an E300 diesel which holds almost 9 quarts of oil. When full, the oil level is about a pint above the sensor's mount (in other words, about a pint spills out when you remove the sensor. Then, it would appear that the level would have to drop at least another inch before the float would move and maybe another half inch to inch before the level sensor would trip. I would say that means on my car the oil would have to be down about 2-3 quarts from full or 1-2 below add on the dipstick before the level sensor would trip. I don't think that MB designed the level sensor in order to let you know when to add oil necessarily, but when the level is so critically low that you MUST attend to it. Apparently the diesels will shut down when the low oil level sensor trips. I don't know if that's true of the gas models but you wouldn't want it to do that if you were simply a quart low, I wouldn't think.

Today's modern cars without dipsticks would have a more refined electronic level sensor that actually tells you to add oil when it is just low...but the older warning systems seem to be just to prevent catastrophic damage...like the "belt and suspenders" approach.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz