Last Updated Saturday, March 10, 2012

Increase Your Gas Mileage by 63%, no wait! By well over 108%.  

Before I gave up gasoline and started exclusively driving my electric truck, I was getting over 50 mpg in my 1992 Honda Accord. This is a 108% increase in gas mileage above the 24mph that this vehicle originally got.

In Part 1, I discussed how to increase gas mileage 41% by reducing speed and performing proper engine maintenance.

Part 2 brought the efficiency increase up to 63% simply by following steps in part 1 and having a tool like the Scan Gauge II 

that can monitor the engine performance in real time. With this instantaneous engine performance feedback, the driver is conditioned into more efficient driving habits.  

Increase Your Gas Mileage well over 108%:  Reduce the Friction

If you don't already have an instant feedback tool like a Scan Guage, I highly suggest you get one now. 

Applying the efficiency tips in this section (and previous sections) will more than double the gas mileage of your vehicle. Imagine getting 36mpg in a vehicle that used to get 18? Or 108mpg in a 54mpg Prius?

This next level of increased fuel economy starts to dip into the realm of “crazy” and the amazing results you will see, require some extreme vehicle modifications that most people may not want to do. I admit that some of these modifications potentially violate Rule #1: Save energy without sacrificing convenience and luxury. But perhaps they can be justified by all the money you can save at the pump.  

Remember to always keep safety in mind when performing any modification to a vehicle.  

Reduce the Friction.  Maybe there's more, but I counted 6 forces that slow cars down. 

  • Road friction
  • Vehicle weight
  • Engine friction
  • Air friction
  • Hills
  • Braking
Any time you reduce friction, the less energy it takes to drive somewhere. This is why a space craft can travel billions of miles using nothing more than a glorified aerosol can for propulsion, there is essentially no friction in space. 

Road Friction: Pump up the tires to the max sidewall pressure. In my 20 years of driving experience, premature tire wear is always caused by improper wheel alignment or too low of tire pressure. Tire failure is caused by road debris or driving on tires that have excessive wear. The only down-side to higher tire pressure will be increased road noise and a slightly bumpier ride. 

The next time you have to buy new tires, spend an extra $25-50 per tire and buy low rolling resistance ones. Also for an even more efficient tire, consider getting a slightly thinner tire.

Any unnecessary vehicle weight will contribute to road friction and degraded performance climbing hills. A 1% vehicle weight reduction will increase fuel economy by roughly 1%. Remove anything with mass that does not contribute to moving you safely from point A to point B. Examples: Extra seats, trunk upholstery and even non-functioning amenities, (I pulled out the following: glove box, stereo, speakers, broken window motor, broken antenna motor, wiring, A/C and the power steering pump).
Carry less fuel: Gasoline is heavy. With my Honda now getting over 50mpg, its 15 gallon tank is now overkill for that car. I get by perfectly fine on only 3 gallons of gas a week.  This in turn reduces vehicle weight by 70 lbs.
Lose Human Weight: If your car weighs 2000 lbs and you weigh 200 lbs, you the driver are adding 10% to the total weight of the car. By loosing weight, you will increase your fuel economy. 

Engine Friction: Use 0W30 synthetic oil. It's a few dollars more but it offers the same protection as 5W30 but claims a 1-2% increase in fuel economy. Remember to only fill to the lower end of the hash marks on the dip stick or else you'll negate any fuel savings. Use Royal Purple gear oil in your differential and manual transmission.  Re-pack your wheel bearings every 50,000 miles. 

Removing parasitic engine loads. Air conditioning and power steering as well as their associated belts and physical weight add friction and increase fuel consumption. 

  • In a smaller vehicle, power steering is absolutely not required. It was invented so frail, old ladies could drive too. Are you an old lady? If not, suck it up and rip out the power steering. While power steering is very helpful for making a 3 point turn in a parking lot, I actually prefer the increased handling that comes from driving at speed without power steering. 
  • While vehicle air conditioning is almost a life saving necessity, I found that even in the dead of summer, I don't use the air conditioning in my Honda all that much. At 5:45AM when I am driving the 20 miles in to work, it's still cool enough that I don't use it at all. After sitting all day in the hot parking lot, my car is so hot, the A/C isn't effective until the last 12 minutes of my commute home. I would roll my windows down for the first 5 minutes of getting on the freeway. At the violation of rule #1 and for the sake of science, I had the R-12 coolant evacuated and I ripped out the A/C compressor, belts, hoses and condenser.  That's 65lbs of weight and parasitic engine load deleted. In return, I put in a beaded seat cover, which by the way, I have never been so comfortable driving during that first 10 minutes of getting into a hot car. 

Air Friction: Remove the spoiler if your car has one. How often do you drive faster than 130mph anyway? An up-side-down wing serves no purpose at 65mph. 

Remove the roof rack from your SUV or mini-van. Only re-install it when you are actually going to use the roof rack. In the 6 years of owning a mini-van, I have used the roof rack twice.  I estimate I have spent an extra $160 in fuel simply because I left the rack on this whole time.  I removed it last month and have noticed a 1mpg improvement on the freeway. 

Braking: Any time you use the brakes you are throwing away money. Anticipate stops ahead of time so you don't have to use your brakes as much. Hard braking should only be done in emergencies, (collision avoidance and reckless driving caused by severe diarrhea).

Hills are inevitable. Use them (over passes, temporary grade changes) to your advantage. Slow down 5-10mph while going up an overpass and speed up on the way down. Energy is conserved and life is good.

By the way, you can actually out perform the the fuel efficiency of cruise control by allowing your speed to fluctuate as you go up and over hills. 

Advanced Driving Techniques:

Pulse and Glide is a driving technique that can add 20% to your fuel economy without having to perform a single modification to your vehicle. The basics behind P&G is you accelerate 5-10mph above your desired speed, put the vehicle in neutral and coast to 5-10mph below your desired speed. Then repeat. The theory is an internal combustion engine operates most efficiently in its' power band. The problem with the power band is it also burns a lot of fuel, only really efficiently. If you can operate at peak power efficiency in small slices and coast the rest of the time, you will improve your gas mileage.  For example, if you normally get 30mpg on the freeway, you may only be getting 20 mpg at peak power efficiency. Since you are operating at peak power efficiency for ½ the time and coasting (or essentially not burning any fuel) the other ½ of the time, your average fuel consumption is 40mpg. Much better than 30mpg if you were just cruising on the freeway. 

I have found that using pulse and glide (+-5mph) in the cruising lane does not impact the flow of traffic nor does it upset other drivers. Do not use this technique in the passing lane. Not only will you upset everyone behind you but passing lane driving is not fuel efficient driving.

Engine Kill Switch: This simple engine modification is a good compliment to the Pulse and Glide driving technique. Shutting off the internal combustion engine anytime it isn't being used is what makes the Toyota Prius get such good gas mileage.  I installed a kill switch in my car so when I engage it, all electricity to the fuel injectors is removed and the engine instantly dies. This prevents a lot of wear and tear on the ignition switch and also keeps the rest of the car's electrical systems still running happily while I coast at nearly infinite mpg. Since my car has a manual transmission, I can easily re-start the engine it by popping the clutch while in 4th or 5th gear. Choosing the correct gear to re-start in allows a nearly seamless re-start (unlike popping the clutch on a push-start). If you end up coasting to a stop, like at a traffic light, simply use the starter motor when the light turns green.  If you are 2nd or 3rd in line at a light, you will have sufficient time to re-start the engine and get it in gear before anyone behind you notices.  
It is absolutely critical to have a well maintained engine that will re-start reliably before killing the engine in traffic.  

Aerodynamic modifications: In theory, without any friction and after getting up to speed, a car should be able to coast indefinitely. At freeway speeds, air friction is the dominate force that slows a vehicle down. Aerodynamic modifications to the car body are super effective because now coasting in a car can be done for a longer period of time before the engine has to kick in again to speed it back up. 

All of these techniques used together yield increases in efficiency well over 120% above EPA. Speaking from experience, my maximum efficiency was 50.6mpg or 111% increase in a car that the EPA states should only get 24mpg.  

See my aeromods page for even more tips on achieving even higher fuel economy. It covers air dams, wheel skirts, under carriage covers and boat tails. Also check out for more tips.

Additional Techniques: 

LED lighting: Replace all the cabin and instrumentation lighting with LEDs. This will also save your battery if your kids leave the interior cab lights on all night. Replace brake and signal lights with LEDs. I have yet to find a suitable retrofit LED headlight but many new cars already have them. The amount of energy saved by going to LED lights approaches 300 watts. With the inefficiencies in the alternator, this adds back nearly 3/4 horsepower to the engine. Not only is this quite a significant fuel savings (especially at night), it also begs the question, “For short trips, is the alternator even necessary anymore?”

Alternator Delete: By reducing the electric draw of the engine and accessories, the alternator really isn't required anymore, at least for a short daily commute. Replacing the regular car battery with a deep cycle one would give the car even more alternator-less driving time, (perhaps in excess of 250 miles). A small solar panel or nightly battery charge would keep the car battery charged each day.

While I can't speak from experience, as I never deleted the alternator in my Honda Accord, there are others who have.  They realized a 10% increase in efficiency.  Imagine no more belts on the engine. How simple and elegant would that be? 

Replace glass windows with plastic: Glass is heavy and replacing at least the side windows with lighter material will reduce vehicle weight. I have yet to try this one either but I will be replacing some cracked glass in my truck later year.  

Next Article:  Coasting In Gear vs. Neutral