I have a 98 Civic and for the last year it's been getting awful gas mileage. I've had it for almost 7 years, up until about a year ago I was getting around 30 to 33 miles per gallon. Now I'm getting around 24pg. The oil has been changed every 3k. Any suggestions??
Did you change anything before your mileage dropped? Tires, transmission fluid, tire pressure, traffic conditions, favorite gas station, new job with a different commute, driving style...there's loads of different kinds of things that can cause your mileage to drop.
I agree with R.I.D.E. The mileage will drop with little or no warning.
Also check for exhaust leaks and/or pinches. My brother once bottomed out his Accord and flattened his tailpipe. He noticed a slight drop in power, but nothing big. However, his fuel mileage dropped from around 28 mpg to about 15.