The colder it is outside, the more my gas milage drops

[nakedfrog]

Originally posted by: jdini76

Originally posted by: d3n
The heater pulls way more amps from the alternator than the AC condenser I think. Maybe that is why. Maybe the denser colder intake air does not flow through the air filter as efficiently.

The only thing running for heat is the blower. there is a heater core in the dash that gives off heat from the radiator.

And they're pretty much always a PITA to replace

 

[AMCRambler]

Originally posted by: Mark R

Originally posted by: AMCRambler

Close. Colder air is more dense and since there's more air per square inch/meter whatever, the mass airflow sensor detects this and the cars computer will increase the mount of fuel it's putting into the engine. Otherwise the car would run lean. Same reason when you put a turbo or super charger on your car you've got to increase the amount of fuel being pushed into the engine, aka fuel pump upgrade, fuel regulator change, larger injectors, etc.

This is irrelevant.

The total power produced by the engine depends on the total mass of air and fuel aspirated by the engine. Except under WOT conditions, this is limited by the throttle, which is controlled by the driver to provide appropriate power for the conditions.

Certainly in cold conditions, the engine is capable of higher total power output because it can aspirate a greater mass of air - but the proportion of time that an engine spends at WOT is so small as can be ignored.

Much more significant are changes in the total energy consumption/delivery:
a) depending on the climate, winter drag may be 10% higher than summer drag - thus 10% additional fuel would be required for the same journey
b) Fuel mix - winter fuel is more volatile (to aid starting) and contains less energy per gallon
c) In very cold weather the engine takes longer to reach operating temperature - efficiency is greatly reduced during the warm-up phase
d) Different driving conditions - idling the car to 'warm-up' the engine is a tremendous waste of fuel; lower speeds may be required in icy conditions (which may be less efficient); different tire performance (e.g. lower air pressure, change in rubber properties)

Ok yes, the fact the car will be producing more power will be pretty irrelevant since the driver will be controlling the throttle accordingly. I believe all your points are valid, I just don't think that would be enough to cut mpg in half.

 

[Jahee]

Originally posted by: Mark R

Originally posted by: AMCRambler

Close. Colder air is more dense and since there's more air per square inch/meter whatever, the mass airflow sensor detects this and the cars computer will increase the mount of fuel it's putting into the engine. Otherwise the car would run lean. Same reason when you put a turbo or super charger on your car you've got to increase the amount of fuel being pushed into the engine, aka fuel pump upgrade, fuel regulator change, larger injectors, etc.

This is irrelevant.

The total power produced by the engine depends on the total mass of air and fuel aspirated by the engine. Except under WOT conditions, this is limited by the throttle, which is controlled by the driver to provide appropriate power for the conditions.

Certainly in cold conditions, the engine is capable of higher total power output because it can aspirate a greater mass of air - but the proportion of time that an engine spends at WOT is so small as can be ignored.

Much more significant are changes in the total energy consumption/delivery:
a) depending on the climate, winter drag may be 10% higher than summer drag - thus 10% additional fuel would be required for the same journey
b) Fuel mix - winter fuel is more volatile (to aid starting) and contains less energy per gallon
c) In very cold weather the engine takes longer to reach operating temperature - efficiency is greatly reduced during the warm-up phase
d) Different driving conditions - idling the car to 'warm-up' the engine is a tremendous waste of fuel; lower speeds may be required in icy conditions (which may be less efficient); different tire performance (e.g. lower air pressure, change in rubber properties)

AND may not actually reach the same peak operating temperature it does in summer temperatures..

 

[randay]

try coasting everywhere.

 

[Zenmervolt]

Originally posted by: Jahee
Colder it is means combustion is more unefficient, the fuel is less volatile and combusts less easily, more of it is wasted, among other things.

Edit, it shouldn't be as much as 50 miles on 3/4 of a tank though... Maybe its something more..

Wrong.

In cold weather, the engine will use more fuel for many reasons. Firstly, there will be a longer warm-up period, during which time modern engines will use a lot more fuel. The faster an engine warms up, the faster the emissions controls start working 100%, and that's cared about more than mileage by the manufacturers. During cold warm-up, fluids are thicker, even in the transmission, which creates more parasitic drag on the engine for the first 15 minutes of a drive.

Additionally, colder air is denser and contains more oxygen molecules per given unit volume. Since an engine pulls in a set volume of air and not a set amount of oxygen, the engine management compensates for the additional oxygen by injecting more fuel.

Finally, the big one. In cold weather stations add anti-freeze to their fuel, this reduces the per-unit-volume energy of fuel and the engine management computer compensates by again injecting more fuel. This is the largest player in the sustained mileage drop in the winter and given the shift in the OP's area to sub-freezing temps, probably the most likely culpret for what he has observed.

ZV

 

[Zenmervolt]

Originally posted by: d3n
The heater pulls way more amps from the alternator than the AC condenser I think. Maybe that is why. Maybe the denser colder intake air does not flow through the air filter as efficiently.

Um... The heater isn't electric. It's a fan that blows air through a miniature radiator (called the "heater core") that is usually mounted in the dash somewhere. The heater core has engine coolant flowing through it and that's where the heat comes from.

ZV

 

[Zenmervolt]

Originally posted by: Jahee
AND may not actually reach the same peak operating temperature it does in summer temperatures..

Wrong except in very, VERY extreme conditions. Unless something is broken. The thermostat will ensure that the coolant temps remain at the design level.

You'd need to be somewhere in Alaska before you began encountering temperatures cold enough to prevent an engine from reaching normal operating temperatures.

ZV

 

[nakedfrog]

I think ZV needs a custom title

 

[Toastedlightly]

/thread.

 

[ballmode]

I have that issue too with the Integra

 

[brandonbull]

Originally posted by: Gusty987
Colder air is more dense than warmer air and thus should give better mileage. And wtf car are you driving that gets 90 miles off 3/4 tank of gas?

M1 tank?

 

[Insane3D]

Originally posted by: Zenmervolt
Finally, the big one. In cold weather stations add anti-freeze to their fuel
ZV

Can you elaborate on this? Are you referring to the ethanol added to winter blend fuel?

 

[Zenmervolt]

Originally posted by: Insane3D

Originally posted by: Zenmervolt
Finally, the big one. In cold weather stations add anti-freeze to their fuel
ZV

Can you elaborate on this? Are you referring to the ethanol added to winter blend fuel?

I do not know what they use in terms of specific chemicals, but I do know that gasoline stations have a winter blend of additives that are effectively anti-freeze for fuel and that the addition of these additives decrease the per-unit-volume energy density of gasoline. This was occuring before they started adding ethanol (and where I grew up they used 10% ethanol year-round since it was the midwest).

However, ethanol does have significantly less energy content than gasoline, so any increase in the percentage of ethanol will also result in a drop in fuel mileage. In areas that only have ethanol in the winter blend of gasoline the mileage drop in winter will be more severe.

ZV

 

[Insane3D]

Yeah, I think we were thinking of the same thing. I thought for a second you were saying they were adding plain old car antifreeze to the fuel and I was like...what?? Then I realized it was you posting, so you couldn't possibly have meant that.

 

[ShadowBlade]

the Mass Airflow Sensor measures the airflow using the temp of a heated filament. If its extremely cold (or hot), the readings wont be as accurate and the air going into the air-fuel mix wont be right.

If its an older car, it might help to clean the MAF. (I saw dedicated MAF cleaner in a Popular Mechanics. I dont feel like digging out the magazine to check, so just google MAF cleaner)

 

[Zenmervolt]

Originally posted by: ShadowBlade
the Mass Airflow Sensor measures the airflow using the temp of a heated filament. If its extremely cold (or hot), the readings wont be as accurate and the air going into the air-fuel mix wont be right.

Not true. There are ambient air temperature sensors in a MAF system that will be used to compensate for the effects of ambient air temperature, so most extremes won't affect metering.

The ambient temperature sensor, combined with an barometric pressure sensor (most modern FI systems have a barometric pressure sensor too) are used to determine the rough oxygen content which is then fine-tuned based on input from the O2 sensor.

There should be no measureable affect on the metering accuracy of a modern FI system under normal temperatures. Sure, if it gets into the 150 degree range, or the -30 degree range you might see some very slight inconsistencies if the ECU programmers didn't cover that range of temperatures when they coded the ECU.

ZV

 

[OrganizedChaos]

winter blend of fuel, drag from oil pump(my oil pressure was up to 50+psi last night at idle), takes a little longer to get into closed loop, more load on the alternator with all the heated accessories going, and warm up time.

 

[senseamp]

Originally posted by: OS

Originally posted by: Gusty987
Colder air is more dense than warmer air and thus should give better mileage. And wtf car are you driving that gets 90 miles off 3/4 tank of gas?

heh, if anything, since cold air is denser, the car has to inject more fuel to keep the A/F ratio correct.

Winnar.
You do get more power though, but less fuel economy. Adjust your driving patterns accordingly, shift earlier, etc.

 

[Jahee]

Originally posted by: Zenmervolt

Originally posted by: Jahee
Colder it is means combustion is more unefficient, the fuel is less volatile and combusts less easily, more of it is wasted, among other things.

Edit, it shouldn't be as much as 50 miles on 3/4 of a tank though... Maybe its something more..

Wrong.

In cold weather, the engine will use more fuel for many reasons. Firstly, there will be a longer warm-up period, during which time modern engines will use a lot more fuel. The faster an engine warms up, the faster the emissions controls start working 100%, and that's cared about more than mileage by the manufacturers. During cold warm-up, fluids are thicker, even in the transmission, which creates more parasitic drag on the engine for the first 15 minutes of a drive.

Additionally, colder air is denser and contains more oxygen molecules per given unit volume. Since an engine pulls in a set volume of air and not a set amount of oxygen, the engine management compensates for the additional oxygen by injecting more fuel.

Finally, the big one. In cold weather stations add anti-freeze to their fuel, this reduces the per-unit-volume energy of fuel and the engine management computer compensates by again injecting more fuel. This is the largest player in the sustained mileage drop in the winter and given the shift in the OP's area to sub-freezing temps, probably the most likely culpret for what he has observed.

ZV

I see your point, but in this case, the driver would use less throttle because for the same throttle he used in summer conditions, it would accelerate more, so to keep the same acceleration, they would use less throttle in winter? reducing the air intake and therefore the fuel injected?

Edit: Also i didnt realise additives had that much effect on a fuel + mileage? is it that big?

 

[Electric Amish]

Originally posted by: Zenmervolt

Originally posted by: Jahee
Colder it is means combustion is more unefficient, the fuel is less volatile and combusts less easily, more of it is wasted, among other things.

Edit, it shouldn't be as much as 50 miles on 3/4 of a tank though... Maybe its something more..

Wrong.

In cold weather, the engine will use more fuel for many reasons. Firstly, there will be a longer warm-up period, during which time modern engines will use a lot more fuel. The faster an engine warms up, the faster the emissions controls start working 100%, and that's cared about more than mileage by the manufacturers. During cold warm-up, fluids are thicker, even in the transmission, which creates more parasitic drag on the engine for the first 15 minutes of a drive.

Additionally, colder air is denser and contains more oxygen molecules per given unit volume. Since an engine pulls in a set volume of air and not a set amount of oxygen, the engine management compensates for the additional oxygen by injecting more fuel.

Finally, the big one. In cold weather stations add anti-freeze to their fuel, this reduces the per-unit-volume energy of fuel and the engine management computer compensates by again injecting more fuel. This is the largest player in the sustained mileage drop in the winter and given the shift in the OP's area to sub-freezing temps, probably the most likely culpret for what he has observed.

ZV

So, you're saying I should add antifreeze to my gas??


What about this theory:

During the winter I run the defroster a lot, but in the summer I rarely use the A/C. Since they use the same compressor causing drag on the engine it could account for the lower fuel efficiency.

 

[dwcal]

Originally posted by: Zenmervolt
In cold weather, the engine will use more fuel for many reasons. Firstly, there will be a longer warm-up period, during which time modern engines will use a lot more fuel. The faster an engine warms up, the faster the emissions controls start working 100%, and that's cared about more than mileage by the manufacturers. During cold warm-up, fluids are thicker, even in the transmission, which creates more parasitic drag on the engine for the first 15 minutes of a drive.
ZV

I'm guessing this is the reason. Just one question for JEDI. How long is the drive to work? Cold starts use a lot of fuel and even more when it's colder outside. If you make lots of short trips, the cold starts really cut into your mileage.

 

[SampSon]

The reasons for lower gas mileage in the winter have been explained already.
Gas mileage always goes down in cold weather.

Now, have you considered that your gas gauge is not working 100%? I know that after a few years mine doesn't read anywhere close to accurate all the time. The gauge showed a huge decrease in gas mileage, but my records at station fillups didnt.

 

[DrPizza]

Look up carnot energy cycle...
Engines are more efficient at higher temperatures. You're operating the engine longer at a lower temperature until it reaches its normal operating temperature.
(However, in my case, I rarely reach that temperature as I only drive 4 miles each way... when it's 60-70 degrees out, the thermostat opens at almost the same time I reach my school's driveway.

edit: hmmmm, on second thought, it's the difference between the outside temp and the burning fuel temp...

 

[eelw]

Sadly my Civic Hybrid is going through this. I can get over 1,000km on a tank of gas during the summer. But now, I'm only getting 700km. And it will get worse as we get more snow storms in the next couple of months.

 

[KK]

My thermostat just the other day got stuck open. Atleast that's when I noticed it. But the last 2 fillups have only got me to around 300 miles, about a 10% decrease from normal. Those fill ups were prior to me noticing that the thermostat was open. Changing the thermostat is going to be a pain in the ass, aleast it isn't stuck closed.