MPG down 3-4, stop 'n go driving to blame?

My '89 Accord has gone from 21-22mpg city to 18-19 in the last 3-4 weeks. I was wondering if stop and go driving could be causing this.

Normally I take public transit and drive no more than 400 miles/month. Lately, I’ve begun a seasonal job which requires an additional 200-250 miles/month on some very congested roads. I was wondering if that could cause the decrease.

The only other thing I could think of was some repair work done recently (new EGR) that could have loosened a vacuum hose. Or the cold weather combined with a switch to 10% ethanol blends, which other posters have noted could cause this decrease.

Not a big deal, was just curious.

All of the above!

Stopping a car is just turning gasoline into heat and brake dust rather than forward motion. So stop-and-go driving will cause a big drop in fuel economy compared to steady speed driving at reasonable speeds.

Cold weather is also a factor. There is more drag on the engine, transmission, wheel bearings, etc. when they are cold. Your tires also lose pressure with temperature drop. Add in the gas used to let the car warm up, if that’s something you do, and throw in increased rolling resistance if there is snow or slush on the roads.

The change-over to “winter blend” gas will reduce fuel economy by a small but measurable amount. Ethanol contains less energy than the equivalent volume of gasoline.

It can’t hurt to check all your vacuum hoses, but I think the other factors are the more likely culprits.

Good answer! Having kept track of mileage on the same car, I found on a typical Chevrolet 305, the city mileage would seldom be more than 18 mpg, while crossscountry driving easily resulted in 22-23 mpg. Cold weather takes a lot of energy to warm up the engine, heat up the bearings and transmission, etc. The only time I ever go higher maileage in the wintere was when I plugged the block heater in and of course did not use the A/C. In other words the A/C relly knocks down the fuel mileage.