Well, I just got back from my yearly trek to see the in-laws for Thanksgiving up in Ohio and I noticed the darndest thing. My MPG decrease when I was in the colder climate of the north (below 40F). When it was colder out, I was only getting an average of 22-24 on the highway (during the flat drives, no hills with cruise control set to 68 MPH). As soon as I got far enough south with the temperature > 50F, my MPG increased to the usually 27-28ish. Am I loosing it? Has anyone experienced this? Is there some mechanical phenomenom that I am not aware of?

 

I actually noticed the same after i got my car back from the dealership after 5 weeks. I was getting around 27 on the interstate. Now i'm getting 22ish. Thought maybe it was just from sitting there for so long *shrugs*

 

Winter gas is the issue. More ethanol, less mpg. Cold northerners have known about this for years.

 

I have had this happen on all my vehicles, no matter what gas is put in, how much cruise control and gas pedaling I do, your mpg is going to go down in the winter just like it does in the heat of the summer. The temp extremes add stress onto the car and make everything work a little bit harder.

For instance, with the Maxima, I go from the 27-28mpg avgs in the Spring and Fall, to about 24mpg avgs in the winter time. It is just the way it is!

 

Weird, i never noticed a decrease in MPG in my 350z. Then again my memory may just be hazy.

 

How do you get such great mileage with your Max? I have an 09 Max that generally gets me 18-20 in the city and 23 on the highway. I do not have a lead foot either, I reset the gauge a few times to test this and it's consistent.

Do you recommend anything I can do to increase the mileage? K&N filter? Different kind of oil? Anything? Besides aftermarket modifications that is.

 

Define don't have a lead foot? For 23-24 in city i have to keep my RPMs below 2000.

 

The mixture of fuel and air is computer controlled and heavier cold air requires more fuel to make the proper mixture as I understand it. I get the best mileage in summer when it is 80 degrees or above but really haven't noticed a huge difference in colder weather...a lot of you guys are leadfoots anyway. We old people keep our foot out of it... My worst tank is still 23.2 and granted there is no very slow, stop and go, strictly city driving done but a light foot is a huge factor....and very hard to do with this car because stomping it is so much fun.

 

Funny/odd, my mpg seems to increase whenever it gets cooler.

 

I wonder if you drive to a colder climate and don't adjust your tire pressure if that could contribute to 1 or 2 mpg???

 

I'd think it was the exact opposite. Colder air is more dense, and therefore has more oxygen per given volume than does warmer air of the same volume. More oxygen yields a better burn and more power. The on-board computer can measure the density of the incoming air (Mass Air Sensor) and adjust the fuel mixture accordingly for consistent power delivery. When it gets too hot and oxygen decreases, the engine management system will dial back the fuel with a decrease in power. This phenomenon is the purpose behind an intercooler on turbo engines. Also, if you watch Sunday's Top Gear where a Porche and an Audi R8 were matched up, the Audi driver was hoping a new location with lower ambient temps would increase performance.

I'd think that the difference in MPG would be from ethanol blends as mentioned - but this would only apply if you saw MPG differences on the same tank of gas.

Another possibility is tire pressure. Air temps directly affect tire pressure. Lower temps = lower air volume = lower tire pressure = more rolling resistance = lower MPG. It's gotten cold in NY; just this morning I checked my tire pressure and all 4 tires were at about 27-28 psi. My pressure was set to 35 psi in much warmer September. I would expect that tire pressure would vary considerably when driving from a cold to a warm locale.

 

Good thought, I thought the same thing and checked my tire pressure half way through the trip. All tires had a pressure > 30 PSI.


I did see the difference in MPG with the same tank of gas, but I am not sure if what you are saying is correct. I would think ethanol blends would only have a role from tank to tank fillup. Am I correct? It was only when I left the mountains of WV/Virginia and drove into NC with temp > 50F that I noticed the increase in MPG.

 

Most efficient combustion occurs when the air to gas ratio is 14.7 to 1. Air density can be affected by its temperature, however, it requires a container. Most have seen what occurs when a balloon is dipped in liquid nitrogen: it becomes more dense and the container actually becomes smaller. Even mixed with fuel it would easily fit into a cylinder and when combusted create explosive amount of power due to the concentration of the charge.

Therein lies the answer. Air that is more dense creates the need for more fuel, the opposite of what is required for better gas mileage.

The above from discovery channel site. The density has less effect than I thought after doing some research. One site listed 9 factors that make mileage less in cold weather including warm up time to best operating temperature and the dense air causing more air drag and less tire pressure plus the winter gas thing we have in the northern states. Viscosity of fluids are a factor and probably each of the factors is miniscule by itself but all add up to a noticeable loss of mileage

 

The effect of air density on an engine's performance has little to do with mileage. Mileage is the energy needed to move 2+ tons of car against air resistance and accounting for all the internal friction. Higher density air allows more gas to be used per power cycle (remember the 14.7 ratio) thereby generating more power. It really means that a 290 hp engine may be 270 hp in the hot desert and 310 hp on a very cold day. Turbos and intercoolers work on the same principle.

 

Winter sucks for Fuel Economy. Idling + Engine warm-up, Reformulated gasoline, Temperature, Tire pressure, etc, etc. All of these factors become larger issues in the Winter versus the Summer.

Here is a good site for reference: http://www.epa.gov/otaq/rfgecon.htm (scroll down to the charts)

 

Actually, mine goes up in the winter (not as much AC needed here in Florida in the winter!)

 

Yeah, I live in Las Vegas so my car loves the cold!

I think for someone that lives in an extremely hot climate really appreciates the wintertime. Summertime here the A.C. compressor just keeps kickin.

I've never actually monitored the MPG but I can definitely say that I use much less gas in the wintertime. I always fill my gas to about the same level each time I fill up and when it gets colder my gas will usually last me a good couple days more.

And that's only filling up half way. I only fill up on "E" and only put 10 Gallons at a time.

 

Seriously, how much cold weather (temp < 40F) do you really get in Florida? I am guess not much!!

 

yeah I average about 18mpg here on Long Island. Now I am stuck in around 16.5mpg thanks to the cooler weather.

 

yea I noticed it summer time I got 14mpg city now im getting 12

 

Ive noticed this as well in the last 2 days I've had to put gas in my tank twice and u usually just stick with $20 a week til I go to jersey cuz gas here in manhattan is ridiculous so I usually just put $20 a week and it usually last me for the week but so far I've had to put 2:3 days

 

this car sucks gas like a drunk in city streets on a cold day

 

Everything being equal (tire pressure and ethynol ratio) every car get lower MPG in the winter due to 2 scientific factors.

a) Colder air requires more fuel to bring it up to the proper combustion temperature for the same power output as warm air.
b) Colder air is denser and causes more aerodynamic drag on the car than than less dense hot air.