I'm new to BITOG and have a 05 Buick Lesabre 3.8 Litre with 69,000 miles. I purchased the vehicle from a friend of a 94 year old lady who had passed away and barely drove it. I changed the oil using 5w30 Valvoline Full Synthetic High Mileage, which is Dexos1 Gen2. I also checked under the valve cover and there is no sludge, just a little varnish, PCV valve is good. It has no leaks. Anyway it has used a quart of oil in 4,000 miles mostly city driving. Also does it matter if I use a Dexos oil? Any ideas on another oil that would work better to stop it from using oil would be greatly appreciated.