How vital is it to use premium fuel in an XT? What would happen to the engine if one used regular instead? I am trying to decide between the XT and the 2.5i, and it just galls me to pay an extra 20 cents/gal. for fuel. I do like its (the XT's) peppy drive however.

I've had a few other brand turbo cars that called for premium and had a provision in the owners manual that would permit regular in emergencys. Unlike an engine that's engineered with high compression and a premium fuel requirement, a turbo engine can automatically lower it's octane demand by cutting back on boost which is what the engine controller automatically does. Most of my turbos did not seem to have much less power when regular was used, but I only used mid grade as my normal fuel. The fuel savings of a couple dollars a tankfull is negligible compared to the amount of the monthly car payment.

How vital is it to use premium fuel in an XT? What would happen to the engine if one used regular instead? I am trying to decide between the XT and the 2.5i, and it just galls me to pay an extra 20 cents/gal. for fuel. I do like its (the XT's) peppy drive however.

 

Use the recommended fuel. If you use a fuel with a lower-than-recommended AKI, the ECU will "hear" knock (thanks to the knock sensor) and retard ignition timing and/or reduce boost. Power output and fuel economy will suffer. What's the point?