VQdriver

this question has been asked by myself and others, but no real answers. why does it drop so much despite no change in driving habit? is it because the air temps are so cold that the fuel doesn't burn as effectively? does it have anything to do with the higher density of the cold air? is the fuel blend changed during the winter rendering lowered fuel economy? focusing on just the climate and fuel, what causes lower fuel economy?

Frank Fontaine

I believe the first and most reasonable explanation is MTBE. Now here's the confusing part--many of us thought of it as a Fall to Spring deal. But if I understand it correctly, it's a year-round thing in 87% of the country. So in that case, it would not explain your mileage drop. But the burning issue relates to oxygen. Again, not a straight answer leading to a conclusion, but perhaps somebody can shed light on MTBE besides the fact that oil refiners could care less about our cars and do things the cheap way for maximum profit.

deezo

iTrader: (3)

Did you also notice the car being more powerful in colder weather?

stose95

one reason is when the main cat's cold the effiecency is low. When its warmed up to normal operating temp, it opens up and expands and fuel efficiency is back to normal. so if you do a lot of short trips
you will get poor fuel efficiency.

njmaxseltd

iTrader: (19)

Cold starts and colder running engines need more fuel.

In the summer time your engine comes up to operating temp pretty quickly. In the winter time it takes quite a bit longer for your engine to completely warm up.

Driving while your engine is cooler uses more fuel. Even thou were fuel injected, think of it as a choke. It's going to take much longer for that choke plate to open up in the winter, then in the summer.

Longer warm up times means you burn more fuel.

On the other hand, a nice long road trip may yield you more MPG in the winter. Cooler air as we all know makes more power! So after your engine is completely warmed up in the winter, you could actually run stronger which in turn will burn less fuel.

Tom

Keven97SE

I agree that would be a contibutor, but I think the main reason is simply that the colder air is denser, which makes more power but consequently also requires more fuel.

I always get my best fuel mileage in higher altitudes. My car really gets good mileage up in like Colorado. Got 33 mpg on the highway there one time (entire tankful). This is because the air density is so much lower. My car made a lot less power but on the other hand the mileage went way up due to the reduced fuel requirement.

mlocke

MTBE is one way to oxygenate gasoline (to reduce emissions), but it's really being phased out state by state because of the environmental concerns (groundwater contamination). Oil companies would actually like to continue to use MTBE as an oxygenate ... they have more control over the supply and thus profit by the use of MTBE versus another way to oxygenate the gas ... Ethanol. The proponents of Ethanol blended gas will tell you this. It can be blended to up to 10% in gasoline with no real adverse affect on modern automobiles. The theoretical loss (because the burning of Ethanol does not create as much energy as gasoline) is 3%. I should note there is an additional benefit to using MTBE - it pushes up the octane level. A side benefit of Ethanol is that it reduces the propensity for your fuel lines freezing - good for those in very cold climates.

I believe your 87% mark is high ... although I've never seen a nationwide percentage. Perhaps in those areas that oxygenated gas is mandated ... 87% of those areas are year around? I do know that oxygenated gas was previously mandated in the winter months where I'm at (greater Seattle, Wa) but is no longer mandated because the air quality is better now due in a large part to rigorous emissions testing (but I don't want to get into that issue). The only place in WA state that it is mandated now is greater Spokane, WA ... some 250-300 miles away.

SonicDust187

iTrader: (11)

Gasoline companies add alcohol to the mixture so that the fuel will burn at lower temp. By doing this efficiency of fuel is decreased and you waste more of it.

VQdriver

so many different answers. all very interesting. i think the engine making more power and the air being more dense has a lot to do with it. when the air first turned cold i could feel the throttle respond so much better. especially during that first fall race when the track is still sticky and the air is cool and dry. that's 13 second NA land!

kramerica72

You are incorrect. Here is a quote from the EPA: "At this time, about 30 percent of this country’s gasoline is reformulated gasoline, of which about 87 percent contains MTBE."

Jr'sMaxima

Kev97se.......

How you got 33mpg here in CO is beyond me! LOL. I live here, and yes, my average mpg is around 23-24, the highest ive seen HIGHWAY driving is about 29-30. Thats some good mileage man!! Maybe you got mods that helped you out some, where as Im stock.

BrianV

iTrader: (9)

When it's colder there is denser air, more oxygen in the same amount of air. The engine generally detects this and releases more fuel, this combination also is what makes colder weather more suitable for racing, etc. Generally the more power or the faster you're driving a car the more fuel it requires, the ECU measures all sorts of things and delivers fuel accordingly.

ymNA

iTrader: (2)

your butt freeze so you tend to drive fast to get home.