There really is no sorcery behind saving fuel, as it is all science and all it takes is a good dose of common sense. As car guys, we love to give our rides a good thrashing, but seeing the fuel gauge drop at an alarming rate on our daily commute sure is a waste, as we’re not enjoying the fuel we spent.
Here are some basic tips, plus a warning of how certain add-on accessories can adversely affect fuel efficiency.
1) Keep your car in tip-top shape.
A properly tuned engine is an efficient engine. Thus, we need to ensure that it is always operating in tip-top condition. Make sure you follow your preventive maintenance schedule religiously. Clogged filters inhibit air or fuel flow, which reduces power and makes us step on the gas pedal more to get decent acceleration. Higher revs with the gas pedal depressed deeper simply burns more fuel needlessly.
A modified engine--when used the same way as a stock engine--has the potential to be even more fuel-efficient because the power-to-weight ratio (especially at lower rpm) is improved. Your engine needs to work less to deliver the same amount of forward motion. But of course, there's always the temptation to floor your throttle and hear the engine sing!
You also need to pay attention to your suspension, engine and transmission supports. Racing teams make sure that a car has no unnecessary movements by designing it with minimal slop in the engine/transmission movement, and making the suspension as firm as possible without reducing traction. This ensures that all the mechanical energy produced by the engine is transferred directly to the driven wheels, rather than being lost through unnecessary movements. Make sure your bushings, supports and suspension are in proper working order.
2) Pump up your tires.
Tires operate efficiently within a certain window set by speed, load and temperature. But there is no directly proportional relationship between the three factors. If you will be driving well within legal speeds (or even slightly above it), with the car loaded to capacity, you can safely pump your tires anywhere from 5psi to 7psi above the manufacturer's recommended tire pressure.
Manufacturers will always indicate tire pressure that will be safe to operate at their extreme limits (lateral or cornering speed and longitudinal or straight-line speed plus load). If you won't be exceeding those limits on public roads (you'll end up with a speeding ticket before you find the limits anyway), pump the tires.
In my experience, almost every mass-market car I've driven has given me great fuel efficiency when I inflate the tires between 33psi (small B and C segment cars) to 38psi (large SUVs). I then dial back or add a bit more depending on how the car behaves.
Note: More modern cars with ultra-efficient low-rolling resistance tires require even higher inflation pressure in the region of 40-45psi. From there, you can add a bit more with no worries. The key here is never to underinflate the tires as rolling resistance increases, and under-inflated tires have greater chances of a roll-over in extreme cornering. They are more likely to be punctured by road debris, or when you hit an unseen bump on the road.
Also, bigger, wider, taller and heavier wheels and tires may look cool and improve extreme cornering, acceleration and braking, but they also increase both rolling resistance and wind resistance--particularly if they stick outside the fenders. These will be noisier, too. I’m not saying not to modify your car, but be aware of the consequences when doing so.
3) Accelerate gently but with confidence.
Once your car hits cruising speed, it uses up very little fuel to maintain that speed. A typical 600-800hp sports car will only use anywhere from 15-30hp to maintain a speed of 100-110kph in top gear (pun intended).
The secret is constant acceleration, meaning you’re not going on and off the throttle, and applying more than a 50% pressure on the gas pedal. Do this until you hit your desired cruising speed.
You can maintain legal highway speed in practically any car by pressing on the gas pedal between 25-30% in top gear. When you do this, the car is using the least amount of fuel to maintain that speed. And the faster your car can legally go on the highway, the sooner you can reach your destination, switch off your engine, and contribute to decongesting the road.
Remember: Accelerating aggressively, as well as constantly changing speeds will severely affect fuel efficiency.
4) Look well ahead, especially on the highway.
Maintain your speed and how lightly you step on the throttle by looking ahead and refraining from unnecessary braking. You can navigate a line through slower moving traffic without slowing down by doing this. Every time you slow down--either by letting off the throttle or braking--you will burn more fuel to accelerate to your desired cruising speed. By keeping your foot constant on the gas pedal, maneuvering around slow cars and trying to maintain your cruising speed as much as possible, you will be saving a lot of fuel. Be alert and cruise confidently.
5) Mind your tint and your A/C, as they directly affect fuel efficiency, too.
A belt-driven car A/C compressor requires anywhere from 4-8hp to drive it. Imagine driving a 108hp Toyota Vios--a good amount of power (and fuel) will be robbed from your engine’s full accelerative potential even when you're just idling in traffic.
Keep your car's A/C system clean, leak-free and smelling good. Replace your cabin filter every six to 12 months to allow the air-con's inlet vents to suck in clean air freely. Clogged filters will require your A/C to work harder, causing even more power and fuel to be robbed from your engine. To add to this, putting light tint helps keep in-cabin temperatures cooler, requiring less from your A/C system to keep occupants chill.
6) Be the downhill master.
I go to Tagaytay twice a week and learned that going downhill is the best place to save on fuel. It's all about maintaining a safe average cruising speed as fast as possible, and simply keeping the transmission in the right gear (a low gear) so you're not riding the brakes all the way down. Best I've gotten? It's 45km/L on an Audi A4 2.0 TDI diesel. In contrast, I can only get about a third of that when going uphill to Tagaytay gently.
7) Don’t lug it.
Lugging is a very bad habit caused by a misconception that driving with low revs saves on fuel, regardless of speed and load. Imagine a gentle uphill ascent on a multi-speed bike. An experienced biker will find the right gear that gives him minimal effort, even if it means pedalling slightly faster. Now picture that biker slotting into the lowest possible gear: He might be pedalling slower, but the amount of effort required to turn the pedals is immense. That’s what lugging is all about. And it’s bad for your engine, which can cause detonation or pre-ignition, which leads to overheating or permanent engine damage.
Don't be afraid to rev your engines. Shift gears at 2,500-3,500rpm for gasoline engines, and 2,000-2,500rpm for diesel engines. The secret is to step on the gas pedal as lightly as possible, again ideally no more than 30% to 50%. If your vehicle cannot maintain the cruising speed you want when doing this, you need to downshift, even if it means the revs will be higher. In the long run this will be more efficient and will protect your engine from damage.
Many of these tips are also skills-based, so you will need time and practice to see any appreciable difference. It might be boring for some, but the satisfaction and savings you get once you start seeing improvements is worth it. I've saved an average of 15-20% on fuel since I started applying these tips. Better efficiency means more fuel for fun runs and track days, when you can really enjoy your car!