Are you following bad advice when it comes to saving gas? Here are some tips you may have heard about that don’t work as advertised:Â
* Using premium fuel instead of regular –Â
“Premium” fuel is a misleading term. The gas isn’t better, it’s just higher octane. If your car’s engine doesn’t need high-octane gas (your owner’s manual will tell you) then you’re just wasting your money by feeding it high-octane fuel. And that’s not all. If you feed an engine designed to burn regular unleaded high-octane premium fuel, your gas mileage will probably decrease because your engine is not designed to burn the high-octane fuel, which reduces its combustion efficiency.Â
* Not using the air conditioning –Â
It’s true that air conditioning draws power from the engine and that’s why many people reason that not running the AC will save gas by decreasing the load on the engine. However, unless you also keep the windows rolled up, any efficiency gains achieved by not running the AC will be offset by the increased aerodynamic drag created by leaving the windows open for ventilation. Cars built before the 1980s – when AC was still a fairly rare option – often had ductwork that provided adequate forced air ventilation to the interior even with the windows closed. But modern cars don’t have that feature, because most modern cars come standard with AC – and it’s assumed you will use it, rather than leave the windows down.Â
* Taking off your tailgate (pick-up truck owners) –Â
There is some truth to this one, but not in the way most people probably think. It’s not the improved airflow over the bed that kicks up the MPGs – it’s the weight reduction that comes from taking off a fairly heavy piece of metal. If you can operate your truck without the tailgate, you might see a slight increase in your MPGs by taking off the tailgate. But don’t go out and buy one of those expensive tailgate nets to replace it – unless you just like the looks or need something to hold your cargo in place – because the cost of the net will cancel out the slight potential mileage improvement you’ll get by taking off the metal tailgate. Â
* Filling up your tires to the maximum recommended air pressure –Â
This is another Catch 22 “fuel saver.” It’s true that by filling up your vehicle’s tires to the maximum allowable air pressure (listed on the sidewall of the tire) you may decrease your vehicle’s rolling resistance, which could, in turn, result in a 1-2 MPG uptick in your fuel economy. However, if you exceed the maximum recommended air pressure (see your vehicle owner’s manual) it is also likely that your tires will wear out faster – and given the average $100-150 dollar per tire replacement cost – it is highly unlikely you’ll come out ahead, money-wise. Also, if you inflate your vehicle’s tires to a higher-than-recommended PSI, it will likely alter both ride quality and handling, as well as increase braking distances.Â
* Turning off your engine at traffic lights –Â
Hybrids do this, so why shouldn’t you? Because hybrids have high-torque starters designed to quickly (and repeatedly) start the gas engine side of the hybrid gas-electric powertrain – and your standard (non-hybrid) car does not. It takes more energy to operate a conventional starter – and will wear that expensive part out sooner – if you overuse it by turning off your car’s engine at every stoplight. You will also put unnecessary load on your battery, which may reduce its life. There are, however, some situations where it does make sense to shut off your car’s engine in order to save gas that would otherwise by used up just idling. If you find yourself caught in a traffic jam or work zone where it’s clear you will be stationary for more than about 5 minutes, shutting down your engine is ok.Â
Throw it in The Woods?
On another note, I have had many customers complain of losing fuel mileage. The most frequent contributing factors that I have found in their cases have been:
a) Lack of Ignition service – not performed – EVER
(this includes, but is not limited to, plugs with tips worn to the porcelain, dead coils, arcing wires, non-arcing cap, etc)
b) Underinflated tires
c) Dragging or seized brakes
d)Obstructed/restricted air filter
So even basic service issues, left unattended, will seriously cripple fuel mileage
Hi Eric,
Forgive me for saying so on your site, but I can attest with 100% accuracy that your tire inflation assumption is incorrect. As you already know with our bikes, manufacture tire pressure recommendations are understated compared to actual pressures required to get even, proper wear from the bike tires. The same is true for virtually every automobile, new or old. There are still few, if any, vehicles that will get even tread wear when run at the car-label pressures. I have witnessed this myself over the last 35 years. The maximum cold inflation pressure shown on the tire is actually within 2-3 psi of what keeps all the vehicles I have serviced, wearing their tires evenly across the tread. With the exception of only a handful of lightweight cars, such as the Honda Fit or similar size/weight cars, 32 PSI is grossly inadequate. In virtually every other vehicle, that pressure has consistently worn the edges of the tires hard on the edges versus the center, by about a 50 to 75% margin. This premature tire wear is a direct result of underinflation, regardless of what any tire label on any vehicle may say to the contrary. The sensation of oversteer that most people experience is just that. They have become accustomed to sluggish understeering, or even the lack of any steering feedback at all due to the modern power steering ability to overpower just about all but an all-out flat.
The bottom line is that the actual wear of the tread on any given vehicle should be the factor used to determine inflation, and not a static sticker in the door jamb. Personally and professionally, I have not seen a tire worn to the belt in the center since the last of the bias-ply tire went extinct. I do, however throw away hundreds of tires every year, worn to the belt at the edges with 1/4″ of tread or more left in the center. This is the case with nearly 90% of the tires that I remove from 1st-TIME customers. My repeat customers no longer suffer this malady at all, provided they maintain their tires where I set them, or have me do it for them.
The one mileage/tire fraud you forgot to mention is the Nitrofil Service. I can elaborate on that later, or not.
Graves
I used to drive a Dodge truck and my gas mileage decreased when I dropped or removed the gate. A friend with a F-150 Ford saw the same thing. The son of the man I used to work under was majoring in Aerospace Engineering at UT Knoxville, along with a couple other students and a prof placed a Dodge truck in their wind tunnel to see what they could.
They found a that a ball of stagnant air forms in front of the gate that actually lowers the coefficient of drag. Drag increased if they dropped, or removed the gate.
mythbusters did a segment on this.. you are exactly right.
I definitely prefer the performance of my 85 Toy longbed with the tailgate off, with the winds in the desert the performance difference is real.
I agree 100%. I have a 1982 El Camino and although I don’t remove the tailgate, there is a huge difference in performance when I leave it down. The further I get above 45mph the more it’s noticeable.
My El Camino has a tight fitting custom tarp. It not only increases fuel mileage but eliminates the buffeting. It shows a high pressure area just in front of the endgate(the tarp is pressed down, acts as a rear spoiler) and the result is a quieter, more stable vehicle with it on than off and the endgate down is a plus when the tarp isn’t on. Of course for 20 years or so the shape of the cab and the bed on pickups has had more to do with smoothing the air and reducing drag than anything else. I noticed on my 93 Chevy I didn’t get the buffeting sound I did with my ’82.