Since about 6 months ago I’ve noticed a significant drop in my mpg, as in from 20 down to 15. I drive a 1998 Nissan Quest with 98k miles, and keep it in very good condition.* The head mechanic at the shop says it’s due to the 10% addition of ethanol that’s being added to the gas. All of the stations here in Austin are adding it.
*New tires, change oil & filters at 3,000 miles, transmission fluid is clear and pink, I try to keep the tachometer as close to 2000 as possible. I only use the air conditioning when really hot and avoid afternoon driving (too hot). I don’t use additives. New plugs about 2,000 miles ago.