MPG drop-off in winter?

[92Pony]

Does anyone else experience a significant MPG drop-off in the cooler months? Last year, through the spring/summer, I was getting a steady 39mpg every fill-up in my '94 (1.9). In December, it suddenly dropped to an avg of 35 or 36, and that became the new mark. Once the warm weather returned this spring/summer, it went back up; throughout the majority of this summer, I got a steady 40-41mpg (I drive like a granny in the 'scort, and rarely use the A/C - it's all about the MPG!! ). Here we are approaching cooler weather again, and last fill-up, I was down to about 38mpg. While 35mpg is still great, I know I can get 41, and I miss it - I want it!! - lol!

Does anyone else experience this? Is it just the way it is - cooler air = more dense air resulting in more fuel being burned? Or would it have to do with gasoline formulation changes for the winter months? I'm just curious............



Wade

[mightymoose_22]

Does your engine run any cooler? Perhaps it is not noticeable on the gauge. My first thought is that the engine is not reaching the same operating temperature for some reason. Possibly a thermostat issue?

[GTP Dad]

Mileage will drop in the winter time due to several reasons. First, you often idle the car longer to warm the engine up thus resulting in increased fuel usage. Also, regardless of the thermostat setting the cold air will cause a denser air charge and cause the fuel mileage to drop slightly. Finally, due to the cooler air the thermal efficiency of the engine will drop because of the colder conditions and fuel mileage will drop as well.

I have seen this happen over the years have noticed lower mileage in all my vehicles so you are not alone when it comes to this issue.

[mightymoose_22]

Bummer... sounds like you need to move to California. I get 40+ year round

[wtousand]

38? 40? I'm jealous. I get about 31 in the summer in town but it drops off to about 28 in winter. I don't warm up unless I have a serious window ice problem that I can't scrape, which isn't very often.

The other day I finally drove a 100 mile trip, eagerly checked it and still only got 31. Shucks.

Which makes me think it runs too cold, possibly the leak-by thermo housing quandry. I'm not sure at what temp the computer and related sensors decide to run as lean as possible.

[GTP Dad]

Check the intake air sensor you may need to change it. When was the last time you changed the O2 sensor? That can effect the fuel mileage!

[Cruize]

Winter gas is blended differently than summer gas. As a result, your winter fuel economy drops off. (This may not apply if you are in a year-round warm state and they do not use winter gas.)

On a slightly similar note, put "winter air" in your tires. If you remember back to chemisty class, PV=nRT. (I think air is considered an ideal gas.) So, as temperature (T) goes down, so will pressure (P). In non-technical words - your tire pressure goes down in the winter due to the drop in temperature, so add air to bring your tire pressure back up to normal.

[12Ounce]

I'm not sure if cold more-dense engine intake air hurts or helps gas mileage. In a "marginal" way the more-dense air surely affects the air drag resistance of the moving vehicle.

And being cold certainly affects all the lubricants in an adverse way. The engine oil has heat sapped off the oil pan and the tranny stays so cold that there are different fill markings on the tranny dip stick.

In very cold conditions, the cabin heat may become a factor.

What ever happened to the "adiabatic" engine Ford was working on?

[mightymoose_22]

Is your car a 4 speed or 5?
Mine is a 5, that could account for the extra mileage...