I had a buick one time. New in 91. Pennzoil every 3-5K. At 180K it got totaled. If you looked at the inside where you fill it up with oil it was as clean as a whistle.

Contrast that to our 98 Merc Mountaineer. Bought it 1.5 years ago. All gummed up and sludged. Owner changed it every 10K.

Merc is finally coming out of it now since i have it on a strict diet.