first things first, this isn't with any bmw motor, i'm sure that one of those would be clacka-clacka-clacking within two changes if you attempted to use such a light oil in such.

the vehicle in question is a 1999 ford taurus with 150k miles on it. i was changing the oil on two vehicles with the ford vulcan 3.0 v-6, the aforementioned taurus, and a 1998 ford ranger with 205k miles. i was in a hurry to go over and mow my grandmother's lawn, so i attempted to change the oil in both at the same time. here's where my story starts. i had previously bought a number of bottles of 5w20 quaker state to try out in the taurus, as ford has retroactively approved the use of xw20 oil in vehicles that required an xw30 in 2002. bill r had said something to the effect that he would not bother trying it out on such an old vehicle, and that i wouldn't notice a gas mileage improvement, which was one of the selling points for the stuff.

in my haste, i accidentally left the drain plug off of the truck whilst refilling it, which caused me to waste 5 quarts of the 10 quarts of the 5w30 necessary to service both vehicle.....long story short, one of the vehicles ended up getting 4.5 quarts of 5w20, as i wasn't in the mood to go back to the store. vehicle was filled up to 1/2 quart below fill mark 4500 miles ago. usual oil consumption was 2/5 -.5 quart between 3000 mile oil changes. checking the level yesterday indicates that the car has used 2/5 of a quart in 4500 miles on 5w20.

i know that oil makers are not yet technologically advanced enough to make a 20 weight oil that is not semi-synthetic, but even when i was using mobil 1 in this vehicle, i'd still see a consumption of 1 quart per 6k miles. any thoughts or explanations as to why my consumption might decrease with this significantly thinner oil? thanks for spending the 15 minutes to read this.