Winter Fuel Economy
02-04-2010, 06:55 PM
#1
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Winter Fuel Economy
Anyone else notice their fuel economy go for a crap in the winter or is my MAF or something @ fault?
The trip computer, (I know it's not accurate, but should be realative), says I'm using a full liter more of fuel per 100 KM now than in the summer. I just bought the car in June of 09.
The trip said 8.9 liters per 100 km in the summer, (which in actuality was 10 liters per 100 as measured), and now it says 9.9.
That roughly converts to 23 miles per US gal summer and 21 US gal winter.
The trip computer, (I know it's not accurate, but should be realative), says I'm using a full liter more of fuel per 100 KM now than in the summer. I just bought the car in June of 09.
The trip said 8.9 liters per 100 km in the summer, (which in actuality was 10 liters per 100 as measured), and now it says 9.9.
That roughly converts to 23 miles per US gal summer and 21 US gal winter.
02-04-2010, 07:00 PM
#2
It's the seasonally adjusted gasoline blend; energy density is sacrificed to increase vapor pressure and maintain cold start driveability. I think the EPA quotes about a 5% decrease in fuel economy.
Last edited by 2slow; 02-04-2010 at 07:42 PM.
02-05-2010, 04:23 AM
#8
Mass of ingested air determines load, so in your case where more air is ingested, more power is produced. To drive at a speed a given load is required. So a reduced air volume is required (less VE) for a given load and ultimate power is increased.
The reduction in fuel economy during the winter is generally a function of fuel composition, cold start enrichment, tire pressure reduction and increased initial oil viscosity; you may be able to throw in increased aerodynamic drag with the denser air, though very minimal.
02-05-2010, 06:39 AM
#10
In addition to the cold and the winter gas, you're also probably down a few ticks from the 6MT. If I drive like a granny (rare) and keep the RPM's down, and use 6th gear as often as possible... there have been times when I've ticked over 30 mpg for extended periods.
If it were me and I were concerned, I'd take notice for comparison in the Spring, and start taking actual measurements, rather than rely on the trip computer.
Last edited by Rochester; 02-05-2010 at 06:41 AM.
02-05-2010, 07:28 AM
#12
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Oxygenated fuel. Starts in Late October and runs thru early March.
Wasn't sure they had the same issues in canada, but I guess this confirms it.
besides that, I hate how my 6MT is so stiff the first couple shifts when it's cold.
Can't wait for warm weather.
Wasn't sure they had the same issues in canada, but I guess this confirms it.
besides that, I hate how my 6MT is so stiff the first couple shifts when it's cold.
Can't wait for warm weather.
02-05-2010, 07:35 AM
#13
02-05-2010, 07:39 AM
#14
Not quite (although my sarcasm detector doesn't work this early).
Mass of ingested air determines load, so in your case where more air is ingested, more power is produced. To drive at a speed a given load is required. So a reduced air volume is required (less VE) for a given load and ultimate power is increased.
The reduction in fuel economy during the winter is generally a function of fuel composition, cold start enrichment, tire pressure reduction and increased initial oil viscosity; you may be able to throw in increased aerodynamic drag with the denser air, though very minimal.
Mass of ingested air determines load, so in your case where more air is ingested, more power is produced. To drive at a speed a given load is required. So a reduced air volume is required (less VE) for a given load and ultimate power is increased.
The reduction in fuel economy during the winter is generally a function of fuel composition, cold start enrichment, tire pressure reduction and increased initial oil viscosity; you may be able to throw in increased aerodynamic drag with the denser air, though very minimal.
(0 °C and 100 kPa), dry air has a density of 1.2754 kg/m3 and at -25C the air density increases to 1.423 kg/m3 which means there is 11% more air per volume at the colder temperature, which means the ECU has to compensate for that extra air
02-05-2010, 08:00 AM
#15
Butane is blended into the gasoline pool to increase vapor pressure/ Unfortunately, butane (as with other volatile hydrocarbons) has a short carbon chain and low energy density.
The EPA's site quotes a fuel economy reduction (on average) of 5.3% going from 77F to 20F (primarily fuel factors).
http://www.epa.gov/oms/rfgecon.htm
http://www.epa.gov/otaq/regs/fuels/ostp-3.pdf
02-05-2010, 08:30 AM
#17
so you are saying you will get the same gas mileage whether the temperature is 0F or -40 F? I don't think so. It will be much worse at -40 than at 0 because the ECU wants the car to run at 14.7 -15.5 AFR and the only way to do that is to add a little more fuel to prevent it from going lean in the denser air.
(0 °C and 100 kPa), dry air has a density of 1.2754 kg/m3 and at -25C the air density increases to 1.423 kg/m3 which means there is 11% more air per volume at the colder temperature, which means the ECU has to compensate for that extra air
(0 °C and 100 kPa), dry air has a density of 1.2754 kg/m3 and at -25C the air density increases to 1.423 kg/m3 which means there is 11% more air per volume at the colder temperature, which means the ECU has to compensate for that extra air
I think that makes sense, but I am certain it will draw more questions.
EDIT: factors beyond air density change efficiency (fuel economy) at low temperatures (i.e. cold start enrichment, warm-up idling, tire pressure reduction, increased fluid viscosities (oils and greases), increased aerodynamic loads (air density), etc...)
Last edited by 2slow; 02-05-2010 at 08:41 AM.
02-05-2010, 08:47 AM
#18
YES, I feel the same way! It shifts easier when I let the car warm up.
OP, I get around 22 MPG driving 80% highway 20% city... hate cold weather...
02-05-2010, 09:01 AM
#20
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OP, I get around 22 MPG driving 80% highway 20% city... hate cold weather...[/quote]
That's about my mix of highway and city as well. So, I guess it's normal. I use 89 octane, by the way.
That's about my mix of highway and city as well. So, I guess it's normal. I use 89 octane, by the way.
02-05-2010, 09:09 AM
#22
That wasn't my point, it was that regardless of temperature (and air density) engine load is determined by mass air flow where more air = more power and constant power requirements require constant mass air flows (for a gasoline engine, under stoichiometric operation). So in your example if an engine needs 1 m3 of air at 0 °C for some operation, it only needs 0.90 m3 of at -25 °C (1 kg for both) and consumes 0.068 kg of fuel in both cases.
I think that makes sense, but I am certain it will draw more questions.
EDIT: factors beyond air density change efficiency (fuel economy) at low temperatures (i.e. cold start enrichment, warm-up idling, tire pressure reduction, increased fluid viscosities (oils and greases), increased aerodynamic loads (air density), etc...)
I think that makes sense, but I am certain it will draw more questions.
EDIT: factors beyond air density change efficiency (fuel economy) at low temperatures (i.e. cold start enrichment, warm-up idling, tire pressure reduction, increased fluid viscosities (oils and greases), increased aerodynamic loads (air density), etc...)
The way you say it, a car needs less air to run in the cold... the engine does not control how much air it needs. It takes in as much air as the engine displacement. Period. An 8 litre engine sucks in 8 litres of air. The ecu doesn't say, " oh it cold outside i only need 7 litres of air right now so let's just suck in 7 litres of air". it still has to suck in 8 litres of air because that is what the displacement is.
02-05-2010, 09:26 AM
#23
See above.
The engine knows the incoming air mass flow through the mass air flow sensor (MAF). At a given engine speed this is varied by throttling (restricting) the incoming air flow from nothing to peak VE at that engine speed (VE varies as a function of engine speed).
02-05-2010, 10:36 AM
#26
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As a senior in mechanical engineering who just took a course in IC engines, I have to say that 2slow is correct. Knight, what I think you're not seeing is that in any situation, the car will adjust according to what it's required to do. When the air is more dense, the engine is able to make a more complete combustion, making more power (work/cycle). Because of this, the throttle does not need to be open as wide as it would when the air is less dense, and therefore nearly the same amount of fuel is used, even though more fuel is required for the same mass of air. Your general theory is correct in that the car needs to maintain stoichiometric A/F ratio, but you have to look at the big picture, especially when discussing something over such a broad period of time as miles per gallon of fuel.
Volumetric efficiency. It's a number that basically compares the actual airflow in when compared to the maximum possible. When knight said our engines take in 3.5L of air every two cycles, he was assuming 100% volumetric efficiency, which actually doesn't happen often.
Volumetric efficiency. It's a number that basically compares the actual airflow in when compared to the maximum possible. When knight said our engines take in 3.5L of air every two cycles, he was assuming 100% volumetric efficiency, which actually doesn't happen often.
02-05-2010, 10:46 AM
#27
You know, I never had this stiff shifter issues until this winter, and I just assumed it was because of the STS mod and the loss of leverage.
But now that you bring up gear oil, I did swap in MT-90 last Spring, which would make this my first winter with MT-90 (and the STS mod). Since everything is fine once it's warmed up, the STS is not the culprit, it's the MT-90 that's making things stiff when cold.
I'm probably not going to do a damn thing about it (except wait for winter to end), but it does explain things. Thanks.
OK now, you and 2slow can get back to arguing about mechanical engineering stuff that 90% of us don't understand. Carry on.
But now that you bring up gear oil, I did swap in MT-90 last Spring, which would make this my first winter with MT-90 (and the STS mod). Since everything is fine once it's warmed up, the STS is not the culprit, it's the MT-90 that's making things stiff when cold.
I'm probably not going to do a damn thing about it (except wait for winter to end), but it does explain things. Thanks.
OK now, you and 2slow can get back to arguing about mechanical engineering stuff that 90% of us don't understand. Carry on.
02-05-2010, 11:17 AM
#28
As a senior in mechanical engineering who just took a course in IC engines, I have to say that 2slow is correct. Knight, what I think you're not seeing is that in any situation, the car will adjust according to what it's required to do. When the air is more dense, the engine is able to make a more complete combustion, making more power (work/cycle). Because of this, the throttle does not need to be open as wide as it would when the air is less dense, and therefore nearly the same amount of fuel is used, even though more fuel is required for the same mass of air. Your general theory is correct in that the car needs to maintain stoichiometric A/F ratio, but you have to look at the big picture, especially when discussing something over such a broad period of time as miles per gallon of fuel.
Volumetric efficiency. It's a number that basically compares the actual airflow in when compared to the maximum possible. When knight said our engines take in 3.5L of air every two cycles, he was assuming 100% volumetric efficiency, which actually doesn't happen often.
Volumetric efficiency. It's a number that basically compares the actual airflow in when compared to the maximum possible. When knight said our engines take in 3.5L of air every two cycles, he was assuming 100% volumetric efficiency, which actually doesn't happen often.
I pulled this out of my head, and I think it's correct (although I hate mixing variables and units, or using units as variables):
Last edited by 2slow; 02-05-2010 at 11:19 AM.
02-05-2010, 11:23 AM
#29
That's about my mix of highway and city as well. So, I guess it's normal. I use 89 octane, by the way.
i get between 23-25 (havent had the car in warm weather yet)
B
Last edited by NissanMan97; 02-05-2010 at 12:45 PM.
02-05-2010, 12:26 PM
#31
To put it simply,
Cruising at 60mph will give you roughly the same fuel consumption in 0 degrees as it will in 50 degrees, assuming the fuel composition stays the same.
The only difference between the two is that in the winter, the VOLUME of air consumed is less, because the mass/volume is higher. In the summer, the VOLUME of air consumed is higher, because the mass/volume is lower.
The reason the change in volume doesn't change fuel economy is because the mass of the air is what determines the amount of fuel needed to keep it at 14.7 and how much power is produced per a given volume.
This is why our cars have a MASS air sensor, not a volume air sensor (flow rate sensor).
Oh and before anyone says it, the car DOES NOT run in richer until the engine reaches operating temperature. I have dis-proven this with my wideband o2 sensor.
I can go and start my car right now in the freezing cold and within 10 seconds, the AFR will hover around 14.4-15.0.
I'm not sure, but this could possibly mean that the car does not run in open loop until operating temperature either. I know that at WOT in open loop, my car runs closer to 12.9-13.2 AFR at 1200rpm.
This behavior may be because I let the car sit for 10 seconds or so with the key on the "ON" position before I actually start the car. This allows the heated o2 sensors to get a small "head start" on the warm up process. (IDK, only reason I can think of)
Last edited by Unklejoe; 02-05-2010 at 12:38 PM.
02-05-2010, 12:28 PM
#32
i get around 24 MPG
in warmer weather i use to get 26 to 28 MPG
I guess with the heater blasting pretty much throughout my 3 hour combined daily commute, 24MPG isn't actually that bad....
I have an auto-tragic btw
in warmer weather i use to get 26 to 28 MPG
I guess with the heater blasting pretty much throughout my 3 hour combined daily commute, 24MPG isn't actually that bad....
I have an auto-tragic btw
02-05-2010, 12:55 PM
#33
To put it simply,
Cruising at 60mph will give you roughly the same fuel consumption in 0 degrees as it will in 50 degrees, assuming the fuel composition stays the same.
The only difference between the two is that in the winter, the VOLUME of air consumed is less, because the mass/volume is higher. In the summer, the VOLUME of air consumed is higher, because the mass/volume is lower.
The reason the change in volume doesn't change fuel economy is because the mass of the air is what determines the amount of fuel needed to keep it at 14.7 and how much power is produced per a given volume.
This is why our cars have a MASS air sensor, not a volume air sensor (flow rate sensor).
Oh and before anyone says it, the car DOES NOT run in richer until the engine reaches operating temperature. I have dis-proven this with my wideband o2 sensor.
I can go and start my car right now in the freezing cold and within 10 seconds, the AFR will hover around 14.4-15.0.
I'm not sure, but this could possibly mean that the car does not run in open loop until operating temperature either. I know that at WOT in open loop, my car runs closer to 12.9-13.2 AFR at 1200rpm.
This behavior may be because I let the car sit for 10 seconds or so with the key on the "ON" position before I actually start the car. This allows the heated o2 sensors to get a small "head start" on the warm up process. (IDK, only reason I can think of)
Cruising at 60mph will give you roughly the same fuel consumption in 0 degrees as it will in 50 degrees, assuming the fuel composition stays the same.
The only difference between the two is that in the winter, the VOLUME of air consumed is less, because the mass/volume is higher. In the summer, the VOLUME of air consumed is higher, because the mass/volume is lower.
The reason the change in volume doesn't change fuel economy is because the mass of the air is what determines the amount of fuel needed to keep it at 14.7 and how much power is produced per a given volume.
This is why our cars have a MASS air sensor, not a volume air sensor (flow rate sensor).
Oh and before anyone says it, the car DOES NOT run in richer until the engine reaches operating temperature. I have dis-proven this with my wideband o2 sensor.
I can go and start my car right now in the freezing cold and within 10 seconds, the AFR will hover around 14.4-15.0.
I'm not sure, but this could possibly mean that the car does not run in open loop until operating temperature either. I know that at WOT in open loop, my car runs closer to 12.9-13.2 AFR at 1200rpm.
This behavior may be because I let the car sit for 10 seconds or so with the key on the "ON" position before I actually start the car. This allows the heated o2 sensors to get a small "head start" on the warm up process. (IDK, only reason I can think of)
Holding the car in 'ON' prior to starting should decrease the time spent in open loop after start-up.
For start-up, there are generally fuel additions made based upon IAT and/or ECT feedback; colder temperatures mean less vaporized/volatilized fuel available for combustion, so more is used. Though I don't know the period for which this applies, and it could be very short as start-up emissions are of great concern to (manufacturer) engine calibrators.
My gut feeling is the car is still in open loop, but the fuel trims for cold starts (based on IAT) only last for a second or two; perhaps until the engine reaches a specific speed threshold to signify successful start-up.
Where do you live?
Last edited by 2slow; 02-05-2010 at 12:57 PM.
02-05-2010, 02:32 PM
#35
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Location: Leicester, Ma
Posts: 1,124
wow you guys get good das mileage in the winter or year round for that matter. i notice in the winter in which i will do 70% around town 30% hiway my mpg from the computer (i know thats not accurate) states 20.9. Using the computer in the summer as well it gets to 24.?. i havent actually taken a full take and did the math by the tank size but..i do know when i got the car in 05 it did get better gas mileage. not by a ton but better. Just to note my last tuneup was prob 35k ago and i actully cleaned my air cleaner today since it gets dirt and junk thrown up from the roads in the winter.
02-05-2010, 03:38 PM
#38
Aw, man. I noticed no one mentioned that to you in your goodbye thread, and good too, because it would have been tacky to dis your new ride the way some people did. However, now that you bring it up... that rotary engine is not exactly fuel efficient. But you probably knew that going into it.
Worth it? I think so. That Mazda is a unique and respectable design, mileage notwithstanding.
Worth it? I think so. That Mazda is a unique and respectable design, mileage notwithstanding.
02-05-2010, 03:41 PM
#39
Aw, man. I noticed no one mentioned that to you in your goodbye thread, and good too, because it would have been tacky to dis your new ride the way some people did. However, now that you bring it up... that rotary engine is not exactly fuel efficient. But you probably knew that going into it.
Worth it? I think so. That Mazda is a unique and respectable design, mileage notwithstanding.
Worth it? I think so. That Mazda is a unique and respectable design, mileage notwithstanding.
no mean to highjack op's thread.
02-05-2010, 04:14 PM
#40
