How to increase the gas mileage of your car

Before I get started, this isn’t your typical “make the most of your fuel economy” article for the average person. This is geared more towards the car enthusiast… if you’re the type of person to make changes (mod) your car, this may be helpfull to you.

I’m assuming you’ve already read the typical “make the most of your fuel economy” articles, which have probably given you tips like changing your driving habits (non-aggressive driving, keeping to non-excessive speeds), keeping tire pressures up, changing spark plugs/performing general maintenance/tune-ups, buying a more fuel-efficient vehicle, keeping the air conditioning off, keeping windows up at high speeds, etc. These are all well-known “tips”, and while they do help, I’ve always looked for more. And here’s what I’ve come up with so far.

  • Lower weight oil – You’ve probably noticed 5W20 popping up at your local automotive shop. Certain (newer) vehicles are designed to run on it, and the key reason for it’s existance is that lower weight oils are thinner, and will help to increase gas mileage. Being thinner usually makes it easier to pump, and in general offers lower resistance to many engine parts that end up in contact with it. Of course, going with a thinner oil than recommended can potentially have adverse side effects on your vehicle (and will most certainly void the warranty on your vehicle if it’s not one of the viscosities recommended by the manufacturer), so whether you want to “risk” trying it or not is a decision you’ll have to make on your own. It also probably won’t make a massive difference in the fuel economy of your car, but sometimes, every little bit helps. On the other end of things, lowering the number before the “W” in the oil rating (ie 0W30 instead of 5W30) can help economy during cold starts. This is more apparant as you get to colder climates, and only really has an effect before the car is fully warmed up, but is something else to consider.
  • Sythetic oil – The only time this is likely to a real effect on your economy is if you live in a cold climate, and it will. If you don’t believe me, buy a quart/liter of Mobil 1 5W30, as well as a quart/liter of regular oil. Put them both outside for a day when it’s -40 outside. Once they’re about -40, try pouring them both. The regular oil will probably pour like molasses. The Mobil 1 should pour much better. Now think about your engine… When you start your car on a cold morning, the regular oil is not going to pump through your engine terribly well. Once they’re both at operating temperatures, they’ll probably be about the same, but for the first few minutes, the synthetic has a distinct advantage. Again, this applies mainly to cold climate areas, and only until the engine is warm. If you live in a nice warm climate, this change probably won’t help you. Finally, some synthetics aren’t “true” synthetics. For example, most “Castrol Syntec” oils are not the true PAO synthetics, and therefore do not offer the same extreme-cold-temperature advantages. If you’re not sure, a good indicator is usually to read the back label of the oil container and see if it mentions the “pour point”. Anything between -40 and -60 is probably a true synthetic.
  • Go to a 4-wire oxygen sensor – If you have a mid-90’s or newer vehicle, you’ve probably already got a 4-wire. Older vehicles often have the simple 1-wire. The benefit of the 4-wire is in two areas. First, it has a dedicated ground wire, which can help to give more accurate, precise readings. The 1-wire gets it’s ground from the exhaust, and if the exhaust is providing a poor ground, it doesn’t read very accurately, and fuel economy can suffer. The second advantage to the 4-wire is that it has a built-in heating element. Why does this matter? Because oxygen sensors don’t operate until they reach a certain temperature, and the ECU (cars computer) in many cars waits for the oxygen sensor before running in a fuel-efficent mode. This of course will really only help while the car is warming up, but again, every bit helps.
  • Make sure your thermostat works – The ECU in many cars also doesn’t go into a fuel-efficient mode until the engine has warmed up. If your thermostat is in poor shape (or stuck open), this may never happen. In addition, a warmer thermostat can in many cases offer better economy than a colder thermostat.
  • Lighten the load – Smaller cars benefit from this more than larger cars, but all vehicles should derive some sort of benefit regardless. The fact is, extra weight in the car is extra work for the engine. If you’re hard-core, you can strip panels, seats, and maybe even replace the spare tire with a can of fix-a-flat (although a big gash in the tire will leave you stranded). If you’re not quite that hard-core, simply removing anything unneccessary (baby seats, subwoofers, etc) can have an effect as well.
  • Aerodynamic modifications – This alone could warrant it’s own article. If you’re interested, do as much research as you can, and mod away. Examples of changes that can be made are rear wheel skirts, changes to the front bumper & air dam, removal of roof racks, side view mirror changes (either removal or replacing with smaller, more aerodynamic ones), and more. Keep in mind, these aren’t changes you can pick up at Wal-mart. Just about everything requires custom work, but in many cases can yield huge results.
  • Engine, transmission, and mechanical modifications – there are many, but here are a few to look into…. I suppose I *could* list them all individually, but there are two types of people… those who will probably do them all, and those who won’t do any. They all involve pulling out a socket set, so they aren’t for some people… Lightened flywheels, aluminum underdrive pulleys, custom “economy” camshafts, hi-flow catalytic converters, mufflers, and filters, new “taller” transmission gearing, and custom ECU’s tuned for max economy.
  • LED bulbs – This effects the electrical load of your vehicle and will probably only be noticable (and barely) on smaller cars. LED bulbs use much less power than regular bulbs. Less electrical draw means less load on the alternator, which means less engine work required to turn the alternator. You can find replacement LED bulbs on eBay. Just make sure you get LEDs that are at least as bright as the regular bulbs on your car (side marker lights might not be as critical, but brake lights certainly are). AFAIK, headlights are not available in LED form, but all the other bulbs usually are. Two things to note before spending your money on LEDs are… First, many signal flashers are not compatible with LEDs (they’ll cause your signals to blink fast, similar to the fast-blink when a bulb is burnt out). Some flashers do work, but many don’t (though you can often buy LED compatible flashers as well), so don’t go buying LED replacements for your signals until you know for sure. The second thing is that some vehicles will tell you when a bulb is burnt out, and they may detect the low current draw of the LEDs as a burnt out bulb.
  • Reduce other electrical loads – Keep the fan off if you don’t need it, don’t install high-powered stereo systems, don’t forget to turn off your headlights once it gets bright enough outside, etc. These things all help to reduce the load on the alternator, and are obviously both free and easy to do.

That’s all for now, although I’ll be sure to update as I come across other things I may not have thought of. Feel free to let me know if you know of other ways to help keep your mpg high (or l/100km low).