Miles per Gallon Go Down in Cold Weather
There are many factors that cause the fuel mileage in cars to go down in cold weather
causing your vehicle to get fewer miles per gallon (MPG). As many people have become
accustomed to monitoring their gas consumption, they have noticed decreases in MPG typically
starting around the beginning of November. According to Click & Clack, the Tappit Brothers, of
the NPR radio program “Car Talk,†it is normal to lose about 10% of your gas mileage in cold
weather, however, there are many reports of 15% or more lost MPG. What is the cause of the
lower cold weather MPG?
Here are ten reasons for lower winter MPG:
1.
Winter Gas.Reformulated Gasoline (RFG), also known as “winter gas†is gasoline with
more oxygen and therefore, fewer hydrocarbons. While RFG is required to be sold in many
states, typically starting around first of November, gasoline refiners regularly adjust the blend
of gasoline sold so that even in states without a RFG requirement, a version of RFG is still sold.
In warm weather, gasoline with too many “light†components evaporates easily and
causes vapor lock, an over-rich mixture that causes excessive evaporative emissions, so heavier
components are added to gasoline. Conversely, in cold weather, too many heavier components
keep the fuel from evaporating, resulting in a lean mixture, hard starts and poor converter light
off, consequentially causing excessive hydrogen emissions. The RFG blend of gasoline is made
by diluting regular gas by adding oxygen, often using ethanol or butane, which has a lower BTU
value than the regular gasoline. It is simple logic to understand that if there is more oxygen and
less fuel in a gallon of gasoline, there will be a lower energy content, and hence, fewer MPG.
While proponents of RFG regularly state that the mileage reduction is in the 1-3% range, many
users report far, far worse results.
2.
Cold Weather Starting.Vehicles use a lot more fuel to warm up to the proper operating
temperature in cold weather; it simply takes more fuel in cold weather to get the engine and
system up to temperature before it can run at peak fuel efficiency.In cold weather, a car’s
computer system measures coolant temperature, engine revolutions per minute (RPM),
throttle position, air flow sensor volume and temperature readings to determine the most
efficient air to fuel ratio (AFR) for warming up. To compensate for a not quite warm enough
engine, the on board computer will keep the mixture rich (excess fuel) to keep the engine from
stalling. After warm up, the computer will adjust the AFR for peak performance, but due to the
density and temperature of the air, even after the engine reaches operating temperature; it still
takes extra fuel (energy) in cold weather to keep it at an efficient operating temperature.
3.
Air Density/Wind.Cold air is denser than warm air so there is more air in the path of
your vehicle creating more resistance for the vehicle to go through. Cold weather is also
typically associated with heavier winds– an additional source of resistance. This increase in
resistance is an additional load on the car’s engine, lowering MPG.
4.
Increased Engine Load.Cold weather drivers typically use more vehicle accessories than
warm weather drivers. Accessories such as the heater, defroster, electric seat warmers and
windshield wipers put an additional strain on the engine which reduces fuel efficiency. For
example, the heater takes heat from the engine, which makes the engine run less efficiently or
causes additional running time before the engine reaches its most efficient AFR.
5.
Fluid Viscosity.Heat reduces viscosity (makes it thinner) and cold increases viscosity
(makes it thicker) of the fluids in a vehicle. There are several fluids and lubricants in a car
engine, such as oil, that make an engine operate efficiently only when they are warm and can
flow easily. Cold weather causes sluggishness of the fluids leading to lower engine efficiency,
reducing the MPG until they fully warm up.
6.
Tire Pressure.In colder weather, tires lose air pressure, as a rule of thumb, one pound
of pressure for every 10 degrees (F) drop in temperature. Under-inflated tires increase rolling resistance and decrease fuel economy. At least this problem can be readily fixed by properly inflating your tires.
7.
Road Conditions.Driving conditions in winter, such as rain, ice or snow, are worse than
the driving conditions in warm weather. The roads are more slippery which often causes wheel
spin upon acceleration. Wheel spinning can also occur when trying to get out of snowy or icy
parking spots. Wheel spinning without going anywhere reduces the MPG. The ability to grip
the road always results in better fuel efficiency. Additionally, the poor road conditions can
cause you to drive at less fuel efficient speeds.
8.
Human Warm up Time.Humans are like cars and need to warm up as well; so many
people start their cars to warm them up before even getting in them. Running a vehicle
without going anywhere certainly reduces the MPG. In addition to the start up, many people
leave the car running for short stops, or while waiting for someone, in cold weather that would
have turned the car off in warmer weather. This is especially true for short trips and people
tend to make more short trips in inclement weather; who drives to a neighbor’s house in the
snow?
9.
Extra Weight.If cold weather brings snow or freezing rain that accumulates on your
vehicle, you are carrying a lot of extra weight. A car covered with icicles could easily weigh an
extra 100 pounds; extra weight means fewer MPG. It is also safer to drive without a snow
covered vehicle, so remember to clean off snow and ice as completely as you can (don’t forget
the roof!), not just the windshield
10.Headlight s. Since cold weather is typical of the winter, which has fewer hours of sunlight
than the rest of the year, there are more hours spent driving with the headlights on. The
headlights take additional power which reduces the MPG.
The above information is compiled from information believed to be reliable. If you
would like to add other items to this list, please contactLou .Elwell@Vo rt exFu elSaver.com,
Chairman ofwww.Vo rt exFlu id Optimiz er.com, manufacturers of the Vortex Fuel Saver
Remember the days when you needed to pull the choke out. If these engines had these i think in this weather mine would be out all the time
