4 ms·

My fuel economy drops about 20% on my petrol car in cold weather city driving. I don't know what causes the difference, perhaps waiting for the car to warm up a

My fuel economy drops about 20% on my petrol car in cold weather city driving. I don't know what causes the difference, perhaps waiting for the car to warm up and windows to defrost.

St-Clock 4y ago
Winter tire (if you have them) and heating are the likely culprits!
- Hamuko 4y ago
  Heating shouldn't take any fuel efficiency in a petrol-powered car since the heat is (usually) just a by-product of the engine's inefficiencies.
  - kube-system 4y ago
    Letting the vehicle idle in the driveway while the windshield defrosts will decrease fuel mileage, because the engine runs for longer.
    - Hamuko 4y ago
      It's not really the fault of "heating" that you're idling your car unnecessarily. I'm definitely not idling my car to defrost my windshield, as I'll most likely pre-heat my car, or if I don't, I'll scrape the frost off.
      - kube-system 4y ago
        I feel like we’re losing context here. My comment wasn’t in reference to what I do, or what you do. It was in reference to what the root comment said they did. The person in the root comment proposed that their practice of letting their ICE car warm up to defrost in the winter may lead to decreased gas mileage. This is correct; it will.
      - cameronh90 4y ago
        The reason I idle before driving is that even after I scrape the ice off, the wipers don't seem to be as effective until the window is warmer, and it's blurry and gets foggy. I try and scrape, wipe and antifreeze as much as possible, but I still find I can't see as well until the windows warm up a bit.
- cpsns 4y ago
  Heating would have no real impact, ICE cars are heated using the heat their engines naturally produce. Winter tyres though and winter fuel mixes? Those definitely have an effect.
Someone1234 4y ago
EVs upsides and downsides should be considered without it needing to be a comparison to ICE. But, yes, running the heater will use fuel. In this case EVs with "250 miles" range are losing 30%~ of that range for three months of the year and a further 20% over the first three years of their life, making them reliably closer to a 140-mile vehicle. People who are planning round-trip travel or commuting need to know this information, and unfortunately a lot of EV fans like to mock people for wanting high initial EV range as if winter and or capacity loss aren't real (even with the facts being readily available). The Bolt is currently the best budget EV by far, but people buying it should consider it a 150-mile range vehicle with "bonus" miles above that.
- jmclnx 4y ago
  > for three months Many places in the US, it is more than 3 months :)
  - lazide 4y ago
    In northern Michigan, it was more like 3 months of not bad weather, hah.
- pandaman 4y ago
  > But, yes, running the heater will use fuel I imagine it is so on some air-cooled cars (VW "Beetle", old 911 etc), but on most cars the cabin is heated off the engine's cooling system and does not require additional fuel, so it technically will "use fuel" but no more than the normal operation of the car.
  - organsnyder 4y ago
    OEM aircooled VW heat came from air heat exchangers that took extracted heat from the exhaust gas. Worked terribly when new, and even worse when rust hit: the channels carrying the air from the rear to the front of the vehicle were among the first parts of the body to rust out (at least in Beetles), and if any perforations developed in the heat exchangers you'd get CO going into the cabin. There were aftermarket gasoline heaters available, which is probably what you're thinking of.
jeffbee 4y ago
Same and I don't even get cold weather here on the Pacific coast, just high 30s at worst. The engine on my hybrid runs a lot more in colder weather trying to heat itself and the cabin, even with the cabin thermostat set to 65. For short trips around town I get MPGs in the teens while in the summer I would normally expect 50+ MPG.
kevin_thibedeau 4y ago
Cold air is denser and takes more work to push through.
- hanche 4y ago
  This. At highway speeds, air resistance dominates the energy consumption. It is roughly proportional to air density, which in turn is inversely proportional to temperature. Compare a nice summer day at 300 K, say, to a really cold day at 240 K. That’s a ratio of 5:4, pretty close to the 20% figure mentioned.
Arech 4y ago
Warming up the whole car (including grease in wheel hub bearings, for example, that becomes much harder in cold) takes a lot of energy, so perhaps it is it. I'd say that a fully warmed car though should be a bit more efficient due to a bigger temperature difference and a bigger oxygen amount going into cylinders.
- lazide 4y ago
  People drive differently in really cold weather - they tend to idle the vehicle more (and spend time in it while idling more), drive slower, and on mushier surfaces (snow/slush/ice), etc. and that is without figuring mechanical stuff like thicker oil. If someone isn’t driving highway distances all the time, ‘warm up’ is quite inefficient for ICE vehicles, and tends to run very rich. Totally right that if those factors aren’t there, it should get better fuel economy.
deleted 4y ago
[deleted]
twobitshifter 4y ago
In addition to the points made by others, winter gasoline blends lower fuel economy
- godsfshrmn 4y ago
  Mostly this because you can easily tell when the switch occurs on your mpg gauge, but also increased friction from higher viscosity of lubricants, denser air and subsequent drag increase, increased tire rolling resistance etc
dm319 4y ago
Decreased efficiency of a cooler engine too?

My fuel economy drops about 20% on my petrol car in cold weather city driving. I don't know what causes the difference, perhaps waiting for the car to warm up and windows to defrost.

St-Clock 4y ago

Winter tire (if you have them) and heating are the likely culprits!

Hamuko 4y ago
Heating shouldn't take any fuel efficiency in a petrol-powered car since the heat is (usually) just a by-product of the engine's inefficiencies.
- kube-system 4y ago
  Letting the vehicle idle in the driveway while the windshield defrosts will decrease fuel mileage, because the engine runs for longer.
  - Hamuko 4y ago
    It's not really the fault of "heating" that you're idling your car unnecessarily. I'm definitely not idling my car to defrost my windshield, as I'll most likely pre-heat my car, or if I don't, I'll scrape the frost off.
    - kube-system 4y ago
      I feel like we’re losing context here. My comment wasn’t in reference to what I do, or what you do. It was in reference to what the root comment said they did. The person in the root comment proposed that their practice of letting their ICE car warm up to defrost in the winter may lead to decreased gas mileage. This is correct; it will.
    - cameronh90 4y ago
      The reason I idle before driving is that even after I scrape the ice off, the wipers don't seem to be as effective until the window is warmer, and it's blurry and gets foggy. I try and scrape, wipe and antifreeze as much as possible, but I still find I can't see as well until the windows warm up a bit.
cpsns 4y ago
Heating would have no real impact, ICE cars are heated using the heat their engines naturally produce. Winter tyres though and winter fuel mixes? Those definitely have an effect.

Someone1234 4y ago

EVs upsides and downsides should be considered without it needing to be a comparison to ICE. But, yes, running the heater will use fuel. In this case EVs with "250 miles" range are losing 30%~ of that range for three months of the year and a further 20% over the first three years of their life, making them reliably closer to a 140-mile vehicle. People who are planning round-trip travel or commuting need to know this information, and unfortunately a lot of EV fans like to mock people for wanting high initial EV range as if winter and or capacity loss aren't real (even with the facts being readily available). The Bolt is currently the best budget EV by far, but people buying it should consider it a 150-mile range vehicle with "bonus" miles above that.

jmclnx 4y ago
> for three months Many places in the US, it is more than 3 months :)
- lazide 4y ago
  In northern Michigan, it was more like 3 months of not bad weather, hah.
pandaman 4y ago
> But, yes, running the heater will use fuel I imagine it is so on some air-cooled cars (VW "Beetle", old 911 etc), but on most cars the cabin is heated off the engine's cooling system and does not require additional fuel, so it technically will "use fuel" but no more than the normal operation of the car.
- organsnyder 4y ago
  OEM aircooled VW heat came from air heat exchangers that took extracted heat from the exhaust gas. Worked terribly when new, and even worse when rust hit: the channels carrying the air from the rear to the front of the vehicle were among the first parts of the body to rust out (at least in Beetles), and if any perforations developed in the heat exchangers you'd get CO going into the cabin. There were aftermarket gasoline heaters available, which is probably what you're thinking of.

jeffbee 4y ago

Same and I don't even get cold weather here on the Pacific coast, just high 30s at worst. The engine on my hybrid runs a lot more in colder weather trying to heat itself and the cabin, even with the cabin thermostat set to 65. For short trips around town I get MPGs in the teens while in the summer I would normally expect 50+ MPG.

kevin_thibedeau 4y ago

Cold air is denser and takes more work to push through.

hanche 4y ago
This. At highway speeds, air resistance dominates the energy consumption. It is roughly proportional to air density, which in turn is inversely proportional to temperature. Compare a nice summer day at 300 K, say, to a really cold day at 240 K. That’s a ratio of 5:4, pretty close to the 20% figure mentioned.

Arech 4y ago

Warming up the whole car (including grease in wheel hub bearings, for example, that becomes much harder in cold) takes a lot of energy, so perhaps it is it. I'd say that a fully warmed car though should be a bit more efficient due to a bigger temperature difference and a bigger oxygen amount going into cylinders.

lazide 4y ago
People drive differently in really cold weather - they tend to idle the vehicle more (and spend time in it while idling more), drive slower, and on mushier surfaces (snow/slush/ice), etc. and that is without figuring mechanical stuff like thicker oil. If someone isn’t driving highway distances all the time, ‘warm up’ is quite inefficient for ICE vehicles, and tends to run very rich. Totally right that if those factors aren’t there, it should get better fuel economy.

deleted 4y ago

[deleted]

twobitshifter 4y ago

In addition to the points made by others, winter gasoline blends lower fuel economy

godsfshrmn 4y ago
Mostly this because you can easily tell when the switch occurs on your mpg gauge, but also increased friction from higher viscosity of lubricants, denser air and subsequent drag increase, increased tire rolling resistance etc

dm319 4y ago

Decreased efficiency of a cooler engine too?