Sudden (apparently) decline in gas mileage?

[89Vette]

You're blaming the wrong culprit. It's the winter gas' high Butane level. I think it's more noticable this year due to new polution regs.

Well this is the first winter with E10 (where we didn't have a lot of snow). With all the warm weather, people should be seeing higher avg MPG than E10 might dictate. (FWIW, if you didn't know: Alcohol returns less energy (BTUs) for a given combustion cycle. So, there's no way we'll get the same MPG as the 100% gasoline days.)

Have you tried Lucas fuel treatment? Cleans the injectors and plenum and boosts mileage, noticably. My wife (she drives one, too) and I are averaging 330 miles per tank now, almost 400 in the summer without the Lucas then, to counteract the Butane which leaves us in the spring. Hope this helps.

330? 400? It seems fairly hard to believe these vehicles are getting 20mpg on E10 (or gasoline for that matter)? The only way I could see that being close is if on long, continuous highway runs. That's because I've never gotten much over 250/tank. Jerry Lemond says it's really impossible to improve MPG over what I'm getting.

If this is really true, please say more about tires/wheels and percentage of hwy miles being run. Even the speed on the hwy would be relevant.

Any other mods (or significant service) too! Intake gasket? fuel injector swap? tuning?