My car starting using more oil than usual a few months ago. I was running Mobil1 10w-30 for most of the car's 2 year life, interspersed with some Redline oil runs. It started using a full quart of oil between 3,000 mile OCI's earlier this year, when it usually would never use more than 1/2 a quart at most. I ran Redline 10w-30 on the 2nd last OCI to see if it would have any effect and it also used a full quart of Redline oil on that run. My last run I decided to use Castrol GC 0w-30, the car used a bit less oil on that run, maybe .75 quarts or slightly less. I've now gone back to Mobil1 10w-30 and it hasn't used a drop in 1,000 miles. The reason I went back to Mobil1 is because I find the engine is more responsive and seems to run smoother on Mobil1. The Castrol ow-30 seemed to make the engine more sluggish. So I'm wondering if the Castrol GC had cleaned up some sticky rings or something. I thought the Redline would have done that more than the Castrol but things seemed to have changed after the Castrol GC run. I know recent Castrol ads in auto magazines tought its cleanliness attributes, but who really knows. The only thing that has changed recently is that I changed to a hotter set of spark plugs, my previous plugs were a tad too cool (heat range wise) so I went back to a hotter plug. The engine is a 2.4L turbo, which runs very rich at wide open throttle and high rpms. any opinions would be cool. thanks !