Warmer Temps Give Better Mileage?

Summer gas has been available in Chicagoland for at least 4-6 weeks and as a result my gas mileage has been increasing. What's odd is that when the temp. gets around 60-70 degrees my mileage increases.

 

The spring season around here has had both hot and pretty cool temps and it always seems that my mileage suffers when temps drop. This seems counter intuitive because colder dense air contains more O2 per volume and in the NA cars I've owned this has helped mileage. Not so with the Legacy turbo. Weird.

It's the change in gas from the winter mix to summer mix.

^ Like I said, summer gas has been around in these parts for some time now. I put about 500 predictable miles on my car each week and know the hills and how the winds affect my mileage. It is weird that when the temps climb that my mileage goes along with it. That same thing happened with winter gas as well but not to the same extent.

my milage goes up slightly during the warmer weather but what really helps is i never set my climate control in "Auto" unless i want the AC to run that makes almost a two miles per gallon difference in combined driving. bosco

I've noticed that the mileage has increased as the temp has gone up as well. Maybe its something with the fact that the less dense the air the less fuel is needed to ignite with it so the engine is running more efficiently. Same concept with warmer engines? I dunno, I'm just talking out my hind quarters right now.

Gas also expands around 60 degrees. I don't know how that would work to your advantage. Maybe if you bought gas in the cool morning hours and only drove you car when the temps were above 70...I could see that maybe giving you some extra miles. I think gas expanding usually works against you. There are a bunch of lawsuits against stations who warm their fuel to fill your tank yet actually give you less gas.

 

Anyone?

I think it is because your flip-flops don't weigh as much as your winter boots...hence a lighter touch on the go pedal.

Part of it is the air density as it relates to temperature. Sure, cold air might be better for the intercooler and you end up feeding more air into the engine, but you also have to punch a hole through the cold air driving through it. At some point, there is an optimum point where everything balances out.

Maybe your tire pressures have gone up with the warmer temp... so now you're running higher pressures all around.

16.2 lifetime avg and proud!

another thing the cooler the temp the longer the engine is in the enrichment mode. bosco

I think that engines actually work more efficiently in cold weather. If the post combustion specific pressure and specific volume (i.e. pressure and temperature) are constant, then the lower air temperature will result in a lower specific volume, an a larger area inside the combustion curve, hence more work done per cycle. I do know that you get better climb performance at lower temperatures in general aviation aircraft, and they use reciporcating engines too. However, this may be reflecting a different sort of efficiency than fuel efficiency.

I think that engines actually work more efficiently in cold weather. If the post combustion specific pressure and specific volume (i.e. pressure and temperature) are constant, then the lower air temperature will result in a lower specific volume, an a larger area inside the combustion curve, hence more work done per cycle. I do know that you get better climb performance at lower temperatures in general aviation aircraft, and they use reciporcating engines too. However, this may be reflecting a different sort of efficiency than fuel efficiency.

 

Denser air is favourable for lift and I read somewhere that air at 0F can lead to 20% more power than air at 70F. It wierd that the Lecacy turbo reacts differently.

when the coolant temp sensor tells the ecm it's cold outside, the ecm will slightly enrich the air/fuel mix to allow for faster engine warm-up. this amount of enrichment over a period of time can lead to a drop in mpg thru the colder months.......

another thing the cooler the temp the longer the engine is in the enrichment mode. bosco

 

I think this is the main cause.. Every time you stop and start the car in the winter after the car has cooled you are in enrichment mode. I also think there is a little bit of enrichment dialed in during operating temperature when cold air is hitting the temp sensor.

Many reasons why your mileage will increase come summer:

 

1) Summer gas. Summer gas contains more BTU per gallon than winter mix.

 

2) Cold temps increase the time it takes to reach normal operating temp. This is the time when the engine is least efficient. The colder it is, the longer it takes.

 

3) Aerodynamics. Cold air is denser, making it more difficult for your car to travel through.

 

Add in the fact that most people don't check their tire pressures as temp drops (and as PSI drops), people are less likely to keep their car clean (more drag), and the list goes on.

 

I typically see about 4 mpg less during the dead of winter to the peak of summer, and you should too (turbo or not).

 

Happy driving!

3) Aerodynamics. Cold air is denser, making it more difficult for your car to travel through.

 

 

thats why my golf balls don't seem to go as far in the cold . bosco

no, it's because golf balls expand above 60F

 

did we not learn anything here people:eek:

no, it's because golf balls expand above 60F

 

did we not learn anything here people:eek:

 

I don't know about you but I'm learning things about turbo performance that run counter to my NA experience. Denser air always gave better performance on my NAs be it winter or summer formulations. Could the lower compression ratio be that sensitive to aerodynamic drag? I know that wind has an effect but cancelling out that effect (because I know my routes like the back of my hand) I still get better mileage in warmer (not hot and humid) temps.

 

Bosco mentioned something about an "enrichment mode". What is that?

Many reasons why your mileage will increase come summer:

 

1) Summer gas. Summer gas contains more BTU per gallon than winter mix.

 

Winter gas is blended so that it will readily vapourize in cold temps.

 

2) Cold temps increase the time it takes to reach normal operating temp. This is the time when the engine is least efficient. The colder it is, the longer it takes.

 

Takes a good 10 miles for my drivetrain to get fully warmed when its really cold. The engine will be well within normal operating temps in about 5 minutes.

 

3) Aerodynamics. Cold air is denser, making it more difficult for your car to travel through.

 

That should be overcome by more 02 per unit air.

 

Add in the fact that most people don't check their tire pressures as temp drops (and as PSI drops), people are less likely to keep their car clean (more drag), and the list goes on.

 

Tire pressures are maintained at my nominal preference taking into account temp.

 

I typically see about 4 mpg less during the dead of winter to the peak of summer, and you should too (turbo or not).

 

Happy driving!

 

I saw about 2.5 less. I'm thinking that I don't fully understand the engine management system with its turbo turbo interface but still am always happy driving the Spec.B.

 

Happy motoring to you too!

another thing the cooler the temp the longer the engine is in the enrichment mode. bosco

 

After thinking about what you wrote, I think I understand what you are saying but I'm not sure about the concept. In hot and/or heavy load conditions, the ECU will run the fuel mixture richer to prevent knock by in effect cooling the cylinders with gas. Lean burn creates hotter cylinder temps.

 

BTW, unless I want the AC, it's always turned off in my car.

Seemed like I was getting better gas mileage that usual on a 40 minute trip I took yesterday that I do bi-weekly. But, my gas guage sometimes lies...though lately its been better since I scolded it for doing so.

After thinking about what you wrote, I think I understand what you are saying but I'm not sure about the concept. In hot and/or heavy load conditions, the ECU will run the fuel mixture richer to prevent knock by in effect cooling the cylinders with gas. Lean burn creates hotter cylinder temps.

 

BTW, unless I want the AC, it's always turned off in my car.

 

post 14 explains it pretty well. think of it as having the same effect as a choke on a carburated car. when the air temp is cold a liittle extra fuel helps the egine get started and run. bosco

Except, unlike in a carburated engine, we don't have to worry about icing...

Something you're all overlooking.....

 

Colder air IS denser and DOES contain more O2 per unit measure. Since you're putting more air into the same space, you have to add MORE fuel to accompany the larger O2 volume.

 

That's why you notice a drop in MPG even with summer gas on colder days. People make more power in colder weather cause they are able to put more fuel in.