How I Hypermiled My Car.





Introduction: How I Hypermiled My Car.

About: Update 12 September 2017: A very special thanks to Sam Elder, a manager here at Instructables, who tracked down the cause of my lost publications and fixed the issue. Take a bow Sam!

When it comes to my vehicle, I dont care about performance power output. I want a safe and comfortable ride however I want my car to use the least amount of fuel to get me to my destinations.

I'm a one car kind of guy and I don't care about its looks, I aim to own her as long as I can. For folks who have that itch to get a replacement vehicle every 3 years or so then this instructable may not make much sense. For those privileged few of us who keep our cars long term (I mean LONG years!) then this instructable may have some ideas you can use.

Hypermiling (or I guess hyperkilometering depending what unit you prefer) is a bunch of techniques involving driving habits and vehicle modifications to get the maximum fuel economy out of a vehicle. Note that basic periodic maintenance is a given such as regular oil changes, having steering aligned, using fully synthetic oils, proper weight oil for the vehicle, recommended tire pressures, good tires, clean filters and fuel etc.

Some folks do some pretty extreme mods to their vehicles or use unsafe driving habits. This instructable is NOT about that (for example that thing in the second pic). My family and neighbours already call me a mad scientist and macguyver but I certainly don't want another nickname by driving around a car looking like that!

All the tips I have outlined in this publication works for me in terms of fuel economy and safety. I have tried various techniques over the years and I have settled on those I have explained below. These may not work for you! I have simply presented what works for my vehicle and I'm extremely happy with the results.

Here is how I made my car's range on a full tank extend from below 300km to approximately 530km. My car currently gives me 16.21 km per litre of gasoline. Note that all my mods and changes are fully within the legislative requirements of my region and does not violate the safety devices onboard my car. These first hand practices of mine do NOT compromise my or other drivers' safety on our nation's roads.

Step 1: Driving Style.

Gentle acceleration and deceleration goes a long way in terms or wear/tear and fuel economy. My car has automatic transmission but I have read that manual transmissions can offer improved fuel economy.

Each car has its own optimum driving speed for lowest fuel consumption. For my 1999 civic its approximately 80km/hr (which coincidentally is our speed limit here on the highways).

Driving as part of a chain (without riding a person's rear bumper!) is great for reducing air resistance (except for the leader). Remember those documentaries with lobsters migrating? Those delicious crustaceans already knew this energy saving technique.

Coasting downhill (while in drive for automatic transmission vehicles) and also to a stop before applying brakes will contribute to better fuel economy. It has alot to do with predicting the route and driving defensively.

A good example is when I drive my car I get on average 460km but if my wife drives it we are lucky to get 390km. It's all about driving style.

Step 2: Putting in New Fuel Injectors.

I recently replaced the aged 16 year old injectors in my car and the result was immediate. Smoother, quieter engine. The fuel economy increased significantly. Manufacturers don't ever specify a replacement period for fuel injectors however these critical devices directly affect your drivability and fuel consumption.

In my case, the OEM injectors were heavily congested with deposits and at a price of 46USD per injector, to me that is a great price to get the engine happy again. Due to the age of my 1999 car, I intend to replace the injectors in the next 5 years. For you, depending on the age of your vehicle and behavior of the engine, you can vary your replacement interval.

I'm extremely happy with the replacement DIY job which took my only 1 hour at home. Here is the instructable:

Step 3: Replacing Aged Sensors That Affect Your Fuel Economy.

There are sensors in a fuel injected car that directly affect its fuel consumption. Some can last the lifespan of the car and others have a shorter lifespan. Here is a list of sensors I replaced on my engine.

1. Manifold Absolute Pressure (MAP) Sensor: this basically tells the engine controller how much load the engine is under. Although its pure electronic, with heat and airbourne contaminants, it will fail. I recently changed my MAP sensor and the effect was immediate. Here's the instructable I made for that:

2. Throttle position sensors are mechanical in nature and wear with time. Its possible that the reading at idle is higher that OEM requirements. I replaced mine and although there was no noticeable change to my fuel economy, the car accelerated smoother. Here's the instructable:

3. Replacing your Heated Oxygen Sensors (H2OS) is a great idea. If you didn't know this fact then now you know: Most Fuel additives do poison your H2OS! Everytime you put a fuel cleaner or certain other additives, the H2OS becomes sluggish or simply doesnt respond anymore. I have long since stopped using any sort of additive. My water induction setup actually keeps the internals of my engine clean. Even though these sensors can provide good service for 100,000 miles, in reality it will be far less. I prefer to change my H2OS every 4 years to keep a healthy signal into the engine controller. They cost approximately 30USD but I change mines on my own and to me the cost is worth it in fuel savings. Here is the instructable I did for my car:

Step 4: Reducing Electrical Loads.

The less amps the alternator has to supply means it will last a bit longer and less energy is needed to turn it. I basically replaced ALL my car's lights with LEDs. Main headlights, park, rear, cabin, instrument cluster lights etc are all using less power than (urghh vomit) incandescent bulbs.

Using a solar battery maintainer keeps the battery ready for the next start provided you park in sunlight. A 5 Watt panel is a good rating to get energy into the battery.

Step 5: Do NOT Oversize Tire Width.

Narrower tires offers less weight, rolling resistance and wind resistance. I'm not talking about putting bicycle thin tires on your car. Too narrow tires will result in vehicle handling plus braking capability being compromised!

For example I used 205s on my car but switched to 185s. The car has a much longer coasting roll when I release the gas pedal with the 185s. Strange enough the OEM tires when I first bought the car were 185s. Go figure.

Step 6: Using a Warm Air Intake.

I had removed my stock air intake assembly and put a re-useable filter on the throttle body. Warmer air causing the engine controller to use a slightly lean mixture means less fuel for normal cruising.

I dont think this is a good idea for aggressive driving since there is a power loss at the higher rpms but for me with my smooth, "drive and let drive" philosophy, it works great!

Step 7: Warm Up the Car BEFORE Driving It.

When a car is started with an engine block at ambient temperature, it operates in an open loop mode with respect to the Heated Oxygen Sensors (HO2S). Once the temperature guage reaches that middle region then the engine controller will accept readings from the H2OS. When this happens then the engine goes into closed loop mode and less fuel is used for the power required from it.

Warming up for up to 5 minutes prior to stepping on the gas pedal also means the engine is well lubricated internally and of course will experience less wear versus driving off on a now started engine. This is what I chose to do with my car. If you don't wish you warm up then the power of choice is yours!

I had a remote starter installed in 2004 in my 1999 civic and I use it every time. That investment pays off!

Whether you live in a subsidized fuel market like me or have no subsidized fuel, idling even for a little bit prior to demanding load is a good thing for an engine. From large megawatt to smaller output engines, some degree of warming up is necessary.

Step 8: Reducing the Car's Weight.

I dont mean tossing the spare tire and car jack. Please dont do something like that. I did some simple things suchs as:

1. Replace the stock lead acid with a lithium iron phosphate battery. From 40lbs the car now has to carry 3lbs of battery. Been working great since September 2013 and cranks the engine faster than any lead acid! The mounting hardware for the lead acid battery I removed as well. Here's is my instructable on that project!

2. Clean up the engine bay. I removed my stock air intake and certain coolant tubes for the cabin heater I never use in a tropical country.

3. Use aftermarket components for upgrades. I replaced my rear lower control arms with aluminum aftermarket ones for minor weight improvement.

4. Keep only necessary tools in the trunk. Dont overload with tools you dont need during a road side fix.

5. Use alloy rims.

These may not seem much in the way of a 1 tonne vehicle but every bit helps. I myself weight in at 166lbs so I'm no heavy roller.

Step 9: Turning Off That Air Conditioning When Needed.

When overtaking or moving from standstill, a good tip is to manually turn off the air conditioning. Just press that AC button! When you are back up to cruise speed then switch it back on. Of course on really hot days, fuel economy be damned but this is a really helpful tip.

If you wish you can drive with the windows crack a bit. Having them fully down while on the highway introduces ALOT of air drag. I have been using my air conditioning everytime and I still get great range from my gas tank. Just a thought eh?

Step 10: Use Iridium Spark Plugs.

At first I didnt want to acknowledge it but the appeal of long life spark plugs got to me. Iridium spark plugs even though more expensive, do last longer and according to the manufacture they produce a better spark and help fuel economy. Going on 6 years and my spark plugs still work great. I cant say for sure IF they improved fuel economy but I love the fact I dont have to change them as often.

Step 11: Keeping Idle Speed Low As Per OEM Requirements.

Most engines over time will drift from the OEM recommended idle rpm. Try to keep that idle rpm with the OEM recommendation which is actually the lowest you should go without risking stalling the engine. Most folks tend to carry that idle way up higher to do what? Who knows? When an engine is idling really fast, it is gonna burn up more fuel! Keep it low and keep it real.

Step 12: Install a Performance Exhaust Header.

This is only viable in countries that do not have emissions testing. Performance exhaust headers allow easier exit of gases and the benefit of reduced weight. I'm not talking about a loud muffler here to wake up the entire neighbourhood. Leave the stock quiet muffler. Its just the exhaust header replacement to a less restrictive type that allows for a small improvement in fuel economy.

Here is the instructable for my manifold replacement.

Step 13:



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    All good ideas. I believe that any gains you're making are probably negated by idling your car for five minutes every time you drive it. Yes, your mileage will suffer when the engine is cold. But your mileage while the car idles is ZERO! This is particularly true if you live in tropical area; your car will warm very quickly, lessening the cold run time. I live in a four-seasons area and the only time I start my car before driving it is if I have to scrape the windows. Otherwise, I start the car and go.

    I built an instantaneous fuel economy gauge (based on the MPGuino design) several years ago, and being able to see my fuel economy rate while driving has really changed my driving habits.

    If you could clarify something you referenced for me: You state to coast downhill while in gear... If I coast down hill while in neutral or while holding in the clutch, my fuel economy reading skyrockets by about a factor of 6, while the engine drops to idle RPM. But if I coast down hill in gear, after a few seconds my economy reading will state "0."

    Now, this is probably just a "divide by zero" issue and with the microcontroller. But as the reading is pulled from the wheel speed sensor and one of the fuel injectors, it seems to indicate that the fuel injectors are essentially turned off (and also fuel pump as well?) while coasting downhill in gear.... Is this true?

    10 replies

    you can also qhen coast a downhill , put ion neutral and SHUT OFF THE ENGINE .

    that will give you 0-zero fuel consumption and no resistance from the engine braking.

    just hold the direction firmly as the hidraulic assistance will be turned off too

    Modern cars shuts off fuel if the car is cruising, this method is bad because: 1-lost of steering assist 2-brake assist 3- no abs 4-turning on the engine uses alot of fuel (except start-stop systems) and the risk of steering lock !

    very well said! I don't know why y1111 made such dangerous suggestions.

    You're not seeing an error, when coasting down a hill (or to a stop) in gear your cars ECU can shut off the fuel injectors. The cars momentum/gravity is maintaining the engine RPM with a fuel injector setting of "0".

    Coasting in neutral (with fuel injection) will use more gas since now you need some fuel to maintain the engine idle on its own.

    All right! Thanks for confirming that for me. And by error I meant mathematically, as dividing by zero should yield infinity, not zero ;)

    Yes, that's right, and the extension of that is that ANY time you're slowing down, you should try to avoid using the brakes and just take you foot off the accelerator ahead of time so that you reach the right speed at the right time. That's way you won't be using fuel while you are slowing- and you'll be slowing for longer; and you want to be in the highest gear you can.

    The exact way it works on virtually all modern cars is that whenever the revs are above a certain value and you have your foot of the accelerator, the fuel cuts out completely until the revs come down.

    ...meaning a problem with Arduino's math library lol. If I'm dividing by zero, I wanna see holes open up in the sky, or at least the infinity symbol on the LCD!

    I agree. I have a Camry Hybrid and seeing that little bar shift back and forth calms me down.

    US cars of somewhat recent vintage will shut off fuel when coasting in gear. Coasting in neutral is illegal in most states. That being said, if your càr slows down too much coasting in gear, the little amount of idling fuel burned coasting in neutral will easily be offset by overall gas mileage.

    yep, helps out big, but some of the little computers that plug in see this and think the engine is off and will stop recording mileage, so you won't see how much it actually helps. I downshift going downgrade when towing my trailer, helps maintain speed without using the breaks, and shuts off the fuel injectors. Long hills help the mileage number up a few points every time.

    "coasting" when in gear will not be coasting anymore, will be engine braking. then you will loose velocity doing this because it brakes the movement, and then you will need to accelerate again to retrieve that speed and that will cost more fuel in the final results(even with the cutoff fuel system).

    this is only made in when you need to decrease the velocity anyway or if coasting downhill(well but doing engine braking you will waste the potencial energy that could give you more speed when going down)

    If you drive an electric car that displays power readings, you will realize the savings from changing lights is minimal. Even electric bicycles have motors that rate in the 1KW+ range, my car routinely exceeds 85KW on heavy acceleration. Saving ~100W is barely a drop in the bucket.

    Regardless, I changed my incandescent main bulbs to HID as they are much brighter at slightly less power, and changed all signaling lamps with LEDs as well for similar reasons. Between that and the life expectancy of HID and LED vs incandescent, its worth the upgrade. Be ware of LED front beams, there are many vendors selling bulbs that will fit, but put out pathetically minimal light, not suitable to actually drive with at night. Another warning in that using LED lamps can cause weird side effects with some ECUs. My Toyota tacoma will see an LED dome light as a short-circuit since there is minimal resistance, and turns it off (dim flickering, actually). A low-ohm high-power load resistor has to be added to make it actually work, same as the high-beam indicator with my HID lamps and LED turn signals, which brings the power draw back up.

    3 replies

    just the low light is 110w the pair , each rear brake and turn light 20w , each t10 little bulb from rear and etc 5w. so i estimated that can be up to 350w in lamps in a car thats about 0,5cv . 85kw as you said is when the car is accelerating ,when the car is on low load lets say 30-40km/h and 1500-2000rpm for gasolines ones it uses only about 30 or 40 cv (even if the maximum power is 170cv ,250cv etc) so 0,5cv compared to 30-40 is about 2-3 % less charge and its already a significant amount . i bought all the leds for my car on ebay for about 20-25 usd in total.

    so i think this is a little but very simple ,cheap and great mod

    My car is an old classic now. She doesn't fuss for any LED lighting. Newer cars might fuss but there are LED replacements that ensure compatibility with onboard power monitoring devices for those cars.


    In some countries, it's mandatory to have your lights (actual headlights, if you don't have modern daytime running lights) on when the car is moving. The savings will be more severe here.

    Generally a manual transmission improves your mileage by about 10%. Outside the city, only sissies drive automatics (sorry). You just have to control the temptation is to take advantage of the extra torque. In my case, my manual '93 Honda Civic del Slow has no discernible torque (ok, large gaps). I have to wind up engine a bit to shift in traffic but still get 32 mpg city/38+ highway. And my old manual Toyota 2WD pickup used to get at least 33 mpg on the highway, for a cruising range of appx. 700 miles.

    Some excellent ideas here... just a few thoughts. Yes, you save fuel coasting, but if you lose too much momentum, you're going to burn even more fuel climbing the next hill. Look ahead. That's my main tip for high-mileage driving. Don't accelerate when you know you're going to have to slow down. I don't find that "drafting" (using the slipstream of another vehicle) helps all that much. Even if you're not tailgating, you're at the mercy of drivers who slow down and speed up, which decreases your mileage. I have better luck backing off and keeping my speed steady.

    Maybe someone can explain this weirdness, though. My 2013 Subaru (manual) gets a dismal 24-26 mpg if I drive it "normally." If I shifting very smoothly (without letting up on the accelerator all the way) and do a lot of engine braking, it goes up to 28-30 mpg on the same route, same speed. This seems counter-intuitive. I do save money on brakes as well as fuel, though: my mechanic has been asking for years whether I ever use my brakes... I just replaced them for the first time on my Honda at 149,000 miles. The pads were crumbling from old age.

    2 replies

    I could be wrong about this, but based on the instantaneous economy readout on my 2013 Fiat 500 Abarth, it appears that when engine braking, the economy shoots to infinity until I put a positive load on the engine. I would interpret this as the ECM recognizing the lack of load and cuts the fuel injection. This will especially be true if your car has throttle-by-wire as the computer can dictate the amount of fuel to disperse even when your foot is partially on the accelerator.

    As for anybody wondering why a manual gets better fuel economy than an automatic, it is simply due to how each transmission engages the engine. With a manual car, you have a clutch that positively locks against the engine flywheel from friction. When you push the clutch in, it fully disengages -- during a shift, as you let the clutch out, it slips against the flywheel temporarily until is fully engaged. At this point it is a direct 1:1 ratio and no loss of rotational energy exists. With an automatic transmission, a torque converter is the link between the engine and transmission. The torque converter relies on hydraulic pressure to engage the input shaft of the transmission. Since there is no mechanical connection (ignoring lockup converters for simplicity), there will always be a certain level of slippage within the torque converter essentially wasting kinetic energy and converting it to thermal energy (one of the reasons automatic transmissions have oil coolers and manuals do not). I know I simplified this explanation, but if you're interested, I recommend looking into it as the complexities of automatic transmissions are very cool.

    Lastly, I drive 50 miles a day for work and I have added some performance upgrades to my Abarth (Ram/Cold-Air-Intake to bypass the stock air box as well as an aftermarket ECM), and I average 28 mpg. This is with a 1.4L 4-cylinder that I can't help but drive with a lead foot (18 psi of boost is so much fun). With my upgrades, my car is putting out 180-200 hp (stock is 165). It only has a 10 gallon tank yet I only fill up once a week despite driving 250 miles just to and from work.

    Also, tire pressure! Maintain OEM and the life of your tires, safety, fuel economy, and wallet will all benefit.

    Yep, the "infinity" question is the same one I had for mjtrinihobby the other day, and his reply as well as others confirms that some vehicles do shut off the fuel when engine braking