Many urban areas use either (or both) of two common fuel blends to improve emissions... and they often use the blends only during specific annual seasons:
1) "oxygenated" fuel
2) ethanol (alcohol added to gas)
Both additives displace gas molecules so the energy available per gallon of fuel goes down. Thus MPG suffers. If your area switches to oxygenated fuel for example, plan on about a 10 to 15% drop in MPG.
Many owners reported improved MPG after a few thousand miles of engine break-in, especially on the Tau V8. I don't remember as much on the V6... but then I don't pay as much attention to V6 issues since I don't have that engine. A few things though can easily trash MPG:
1) driving habits (duh) Coasting to intersections instead of holding the throttle open until the last minute can make a big difference. Shifting to neutral while coasting
hurts MPG though: if the engine RPMs are well above idle and your foot is off the gas, the engine computer can go to total fuel cut (no need for gas to slow down) but if you shift into neutral the engine RPMs drop to idle pretty quickly - and the computer has to turn fuel flow back on to maintain idle. Of course everybody knows "jack rabbit" starts clobber MPG.
2) dragging brakes, including parking brake. If I let my car creep just a few MPH and then pop it into neutral it'll coast quite a few feet before coming to a stop. Just a slight incline is enough to make it roll on its own. If your car doesn't do that, something is making the brakes drag or cause other resistance to motion. Another simple test: after a fresh start in the morning, drive just a few miles someplace where you can coast to a stop without using the brakes much. Pull over, put the transmission in Park, and get out... put your hand NEAR each
wheel, feeling if any heat appears to be radiating from the brake assemblies. If one
wheel is noticeably warmer than its twin on the other side of the car, that one needs attention. It's normal for the fronts to feel warmer than rear brakes since the front brakes do more than half the work. But the left front and right front ought to feel about the same if everything is healthy. How far does your brake pedal move before braking action really begins? If you feel the brakes engaging with less than an inch of pedal travel, the brake master cylinder freeplay might be too small and that'll lead to dragging brakes - especially once the engine bay heats up.
3) alignment issues - if your steering pulls a bit, that's extra rolling drag on the vehicle
4) high-power accessories (air conditioner, headlights) are extra load for the engine
5) low tire air pressures
6) what does your engine temp gauge read? If it doesn't get close to half scale there is a problem with the cooling system - and too much combustion energy is getting sucked away and dumped out the radiator instead of going to the wheels. Most gas engines convert only about a third of the potential gasoline energy into power at the wheels; a third gets dumped as heat out the tail pipe, and a third is wasted as heat dumped by the radiator. A too-cool engine sucks even more heat away from the combustion process.
edit: my V8 sedan gets about 18 around town (no local freeway driving, just lots of un-timed traffic lights) and 25 to 27 on the highway. The V6 cars should get a little better than that - though not as much as you might expect thanks to the different gear ratios between the V6 and V8 differentials. When I'm a lead foot the around-town MPG drops considerably.
mike c.
