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Gas Mileage-2003 Honda Civic EX

I have a 2003 Honda Civic EX (5 speed manual). I routinely have gotten gas mileage of at least 32-38 mpg. This winter I notice my gas mileage has dropped off to an average of 27 mpg. I live in northeast Ohio.

This is the first winter the car is not in the garage. I have given my spot in the garage to my 19 year old daughter so she doesn’t have to clean her car off before college classes.

I do not sit and allow the car to warm while I remove snow from it. What could be the cause of this change in mileage. My driving habits have not changed. I’m confused. Could there be a mechanical reason for this?

I have kept up with all the required maintenance on the car. Any ideas?

Parking the car outside in the cold weather we have been experiencing significantly reduces your gas mileage. People who live in cold climates and have to park outside usually have engine block heaters installed. These need to be on for only 2 hours or so to preheat the engine. If you install one your gas mileage will certainly improve.

Another major benefit of a block heater is longer battery and starter life and longer engine life before the car starts using oil.

Glad to hear you have carefully kept track of you mileage.

i would suspect no change due to being parked outside.

a 30% drop in mileage is caused by a change in the engine (plugs, wires, ignition)

the car only benefits from being in the garage the first time you start it. when you go to work, or shopping, it is just as cold as not being a garage kept car.

Check your tire pressure. Not all but part of a drop like that.

I agree with Cappy. 30% is too big a change just for cold weather. Parking outside or inside an unheated garage will mmakee 0% difference. Winter will reduce the mileage (winter fuel mixes, cold engines, snow, different traffic etc.), but not likely 30% Now if you add in a lot of short trips that you might have walked in better weather and maybe the lack of some longer highway trips that you take in the summer, then that might add up.

I suspect it is a mix of winter, maintenance (plugs, wires, oil, air and oil filters air pressure in the tyres (Cold temps mean lower pressure in the tyres so you need to refill them.) or snow tyres that don’t get as good a mileage etc.

Winter gas usually has a lower specific gravity than summer gas due to the lighter hydrocarbons added to help cold weather starting. This means lower energy per gallon, reformulating with 10% ethanol also reduces energy content of gas. This partially explains why we get less mpg in winter than in summer.
Back in the mechanical fuel pump days, vapor lock, which was fuel boiling in the gas line, was more likely to happen on a really warm February day than in the heat of the summer because of the higher vapor pressure of winter gas.

Also, driving through snow takes more power than driving on dry pavement.

I’ve also noticed a drop in winter mileage in two cars. It may have something to do with winter reformulation for pollution reasons as well as easier starting, as you point out.