The best way to save on fuel is to not use it at all - ride a bike, use mass transportation, etc. However, there is a rather large subset of the population that live in a suburban prison. The following is a set of techniques used by people that call themselves hypermilers to achieve high fuel economy/efficiency (FE) numbers, save the planet and save their wallets.
Step 1: Tires
Inflate your tires to, at least, the maximum inflation pressure to reduce rolling resistance.
Should you wish to go beyond, that is up to you. Personally, I inflate my tires to around 55psi (they are rated for 44). Please do not attempt on old or visibly damaged tires. My tires are new and in excellent condition.
Modern tires are radially belted - that is, they won't balloon like tires of yore. Keep in mind what you're doing though. You are reducing the contact patch of your tires in order to decrease static friction. This will reduce your overall braking ability. So riding someone's bumper at 80mph is just that much more dangerous. Again, these steps only work when combined - you can't pick and choose.
When it comes time to buy new tires, look for low rolling resistance (RR) tires. While they may not have the same 60,000 mile (or even 40,000) guarantee, they will save you in the fuel department. The Toyota Prius comes equipped with LRR tires.
Step 2: Weight
Take everything out of your car.... Then put back only what you need.
For those more daring, remove your emergency jack and spare tire and be sure to carry a cell phone in case of emergency. AAA is a good thing to invest in - even if you don't plan on following these mileage techniques.
If you won't be carrying passengers, remove your rear seat and passenger seat as this will lighten your load by a couple hundred pounds.
Step 3: Maintenence
Keep your engine in Tune and use the lightest weight of oil as possible. In addition to friction, you also have to combat viscous forces. The thicker the oil, the more resistance your engine has to overcome.
O2 sensors are very critical pieces of equipment - especially the 1st one (primary).
If you have a check engine light (CEL) and your car is a 1996+ model (for US vehicles) - get your car scanned. Certain auto parts places will scan codes for free (such as Autozone). Fixing parts yourself can save a lot of money - that is, only if you feel comfortable doing it.
Step 4: Reduce Driving Loads
- Air Conditioning
- Loud Sound Systems
- Headlights (that means, try driving in the day rather than at night)
Step 5: Instrumentation
Install a trip computer that can give you instantaneous fuel consumption feedback. Then, turn driving into a game - always try to beat your highest score.
Nissan, according to internal testing, estimates gains in fuel economy ~10%
All New Nissan Vehicles will be equipped with fuel consumption instrumentation.
Toyota Estimates 5-10%, and They too will include instrumentation in new vehicles
Step 6: Pulse and Glide
Assume you want to average 35mph.
Start at 40mph and allow your vehicle to decelerate, in Neutral, to 30mph -- this is called the glide.
Then, accelerate back up to 40mph in the same amount of time that your glide took -- this is called the pulse.
For the more intense, glide with your engine off. This will increase your FE number dramatically while gliding in gear will reduce them as you'll be combating engine braking.
This technique has been proven many times over to be an effective way to increase mileage. But, your mileage will vary based on traffic and other drivers. Other drivers will get quite pissed off at your pulse and glide, so use your best judgment.
Step 7: Hills
Avoid accelerating up hill. Try to coast up hill or, at the very least, maintain constant throttle (not speed). Then, while going back down the hill, accelerate back to your cruising speed.
Step 8: Traffic Lights, Stop Signs, Traffic
The instant you see a red light from a brake light or the yellow/red light from a traffic signal - take your foot off the gas and coast. It's no use speeding up into a stop.
The same goes for approaching a stop sign.
Step 9: Acceleration
The best way to accelerate is by keeping your engine at peak torque. This means, accelerating too slow (as you may have been told to do) and accelerating too fast (bringing your rpms up high) are inefficient and will reduce your fuel economy numbers.
Ideally, peak torque at 50-75% throttle.
Step 10: Aerodynamics and Modification
*Blocking your grille has proven to be effective - just remember that your radiator (and grille opening) were designed for the worst case cooling scenario. So monitor your engine temps and adjust your grille opening accordingly.
- Fold your mirrors. If you can, fold your rear view mirrors in. Just be sure to stay in compliance with local laws.
- Belly Pan - A significant amount of resistance comes from the open areas under your car. Covering them with corroplast or some other material can reduce your drag coefficient (Cd)
- Wheel skirts - covering your wheel wells to keep your cars body one contiguous object can help
- Air Dam - see image, if you car doesn't have one already, this can help
- Always Drive with your windows up
Step 11: Pretend You Have No Brakes
If you didn't have brakes, you'd only go as fast as you needed to ensure you could stop at your next destination. That is, don't apply so much power that you'll only be throwing away your engery VIA braking.
Coasting is your friend.
Step 12: Join a Community
Find an online community to talk with and collaborate. There are plenty of people more experienced and knowledgeable than I.
Personally, I'm fond of the people on Gassavers. You'll find plenty of experiments that, quite commendably, follow a scientific method structure.
Step 13: Credits
Images came from flickr searched for using the creative commons licesnce. Some images came from metrompg.com