Cadillac STS Forum - 2005 through 2012 Discussion, Fuel - Regular /Mid-Grade or Premium? in Past Cadillac Vehicle Discussion; had an 01 sts and ran regular with no problems, 03 sts and ran regular with no problems as well. ...
had an 01 sts and ran regular with no problems, 03 sts and ran regular with no problems as well. (Keep in mind these were both leased cars and were turned in around 40 thousand miles so i dont know what the long term effect would be) If the cars were bought i would have probably ran Premium.
I have a 2006 sts v6 luxury package. According to a cadillac salesmen I have been corresponding with (who is very knowledgeable) the sts v6 can get up to 20% better mileage with mid-grade (89 octane) gas. I am trying it out now to see if he's right. Also, he says to go out and drive the car hard for about a week, then drive very conservatively after that. The car will just sip gas and the mileage will definitely improve.
My (very large) dealer was adamant that unless I noticed knock, there is no need to use premium (in my '06, V8 STS-4) ... Therefore, I usually fill with 87 and have not noticed any problem. Power is probably reduced, but not to the degree that I notice a difference (between regular & premium) and am sure I could easily lose my license if I really tried!
Your geographic location can also help to determine whether to use premium or not. Hotter weather can cause pre-detonation, so using premium helps to safeguard against this condition. If you are hellbent on running a lower grades of gas (and yes this is why the sensor are part of the engine, to adjust the timing accordingly) then it is good advice to run a bottle of Techron through gas tank every so often (you can usually purchase four bottle of Techron for less than ten bucks at the major discount warehouses). But quite honestly, higher grades of gasoline purchased from one of the better refineries (Chevron, Mobil, etc.) are by far better for your engine. If you really want to learn more, find the best engine builder in your area and ask them; they will tell and can show you the differences grades of fuel can have on an engine.