The Basics:
What affects how much fuel your vehicle uses.
# The type of vehicle.
# Miles driven.
# Your driving habits.
# Condition of vehicle -- some things you can change, some you can not.
# Fuel
# Weather
Some tips for improving m.p.g. or using less fuel.
# Start by keeping a log of your fuel used, including miles per gallon. ( See the example below)
Benefits of a log --
* Objectively see the effect of changes.
o Fuel type (Unleaded, UL+, Premium, Ethanol blend)
o Fuel from different stations
o Driving style changes (speed, acceleration, using air conditioning)
o Maintenance performed on car.
* It is a way to tell when something is not working properly on your vehicle - from a drop in fuel efficiency.
* Check Gas Stations - Consistency of reading on the pump for number of gallons.
o Some news stories have covered stations which overstate the amount of fuel delivered as displayed on the pump.
* Without a record of fuel consumed, it can be difficult to tell the effects of changes made, especially considering the accuracy and resolution of a typical automotive fuel gage.
The Factors That Effect Your Fuel Economy
* Vehicle Type
o Normally the biggest factor in gas milage. If you are buying a new vehicle, you can check the EPA numbers, or magazines such as Consumer Reports for milage ratings. Some cars can be ordered with a digital miles per gallon display - shows the MPG as you drive. It can be a great tool to learn techniques for improving fuel economy.
* Miles Driven
o As the old tip went, plan and combine trips to the stores.
* Driving Habits
o Watching the digital miles per gallon display on a car so equipped can be informative and impressive. Accelerating a little slower, removing the foot from the gas pedal a little sooner before a stop sign or stop light can make a big difference. After some practice, some AutoTips visitors have reported 20% or better improvements by paying careful attention to these habits. Increased speed increases wind resistance, and lowers fuel economy.
o Probably the easiest and quickest way for most people to improve their gas milage.
+ One visitor said they imagine they have an egg between their foot and the gas pedal to keep their acceleration light.
+ A car's inertia will often take it farther with a light foot on the pedal than we often realize when approaching a stop sign or light. Some practice with letting up a bit earlier on the pedal to anticipate lights can help efficiency.
+ Always keep safety in mind when experimenting with driving habits, not to impede traffic, etc.
o Air Conditioning - The results may be mixed. A/C increases drag on the engine, and tends to lower milage. When traveling on the highway, this drag may or may not be less than the wind drag from open windows.
* Condition of Vehicle (For more info on a particular item, click on the link, use your Back button to return to this page)
o Some vehicles have overdrive, or a Power / Economy switch for the automatic transmission. This can be switched by the driver normally. Overdrive or Economy settings are used to improve economy.
o Wear / maintenance items under the hood and around the vehicle.
+ Fuel injectors- can become plugged. (see the AutoTips Fuel Injectors page)
* Normally accompanied by rough idle or poor acceleration
* Use good fuels, an approved fuel injector cleaner, or professional cleaning by a shop. .
+ Sticking Exhaust Gas Recirculation ( EGR ) valve. Normally not an easy job to replace or clean.
# Some shops have a system that connects that connects to the engine and injects a detergent that cleans both the fuel injectors, and may help clean sticking EGR valves.
+ Spark Plugs and Plug Wires - both routine maintenance items.
+ Vacuum Lines and grommets- can become stiff, brittle and leak vacuum. Check lines especially where they connect to engine or accessories for snug fit. Check grommets around things like the PCV valve, vacuum hoses around connections to engine, fuel pressure regulator, cruise control, power brakes, and on some cars, the vacuum operated heating / air conditioning air doors. Handle hoses with care..
+ Sensors Problems
# Feed the car computer information on temperatures, engine state, etc. (See the Sensor page ).
+ Air / Fuel filter dirty
# Inspect air filter, change as needed. Change fuel filter per manufacturers recommendation.
+ Thermostat - they can fail open or closed. If they fail open, engine does not heat up to proper temperature, and engine mixture runs rich.
+ Oil - keeping it changed at regular intervals reduces engine wear on internal engine components. As engines wear, they loose compression, and then efficiency.
+ Tire inflation - check owners manual, or sticker on door frame for proper inflation. Under inflated tires increase rolling resistance, and decrease milage.
* Type of Fuel
o Your owners manual should state a minimum octane rating for your vehicle. Depending on the part of the country you live in, 87 is a typical rating for the lowest grade of Unleaded.
+ Higher Octane than what your owners manual calls for may or may not help milage. You can experiment.
+ The author has experimented, and on several cars found fuels blended with Ethanol to give 10% to 20% highway milage improvement, depending on the vehicle. It may or may not improve for your vehicle. It is also no longer required for the gas station to list ethanol content on the gas pumps, so it can be difficult to tell if the gas contains it or not. It has been the author's experience that fuel systems in vehicles where ethanol was used tend to stay very clean.
+ You can experiment with different brands of fuel.
* Weather
o In cold winter months, cars tend to get poorer milage.
+ The engine runs richer until it warms up.
+ Headlights can be on for longer periods of time, the alternator has to make up the load, which puts additional drag on the engine.
+ On many cars, when the defroster is on, the air conditioner runs to remove humidity from the air.
o Summer time can also drop.
+ If the air conditioner is used a lot, it puts additional load on the engine.
# At highway speeds, it is offset somewhat by reduced air drag on the vehicle by having windows closed.
Example Log (A small notebook from an office supply store can be kept in the glove compartment for the log. )
Date Odometer Cost Gallons Fuel Type Station MPG Comments
4/1/00 24,100 14.39 10.0 UL + XYZ Oil Co. @ hwy exit 24.2 Fill Up - Gauge showed 1/2
4/8/00 24,475 20.63 13.76 UL + Energy Oil Co.
1st & Main 27.3 Fill Up- Gauge showed 1/4
To & from work driving
4/15/00 24,785 15.70 10.2 UL + Energy Oil Co. 30.4 Fill Up - gauge between 1/4 & 1/2
To & from work.
Tried accelerating easier since last fill.
To Calculate Miles Per Gallon take
{Current Odometer Reading - Last Odometer Reading) / Gallons used since last fill up.
From the example above for the last two rows
(24,785 - 24,475) = 310 miles driven on the tank since the last fill up.
310 miles / 10.2 gallons used = 30.4 miles / gallon
Note this only works properly using fill up to fill up, since putting less than a fill up would not tell how much fuel was used to arrive at the same reference point.