Truth And Lies About Fuel Saving Tips
September 1st, 2008 Posted in Eric Peters, Fuel, Tips
By Eric Peters, Automotive Columnist
Everyone’s jumping on the “save gas” bandwagon — understandably. It’s on everyone’s mind. But that doesn’t mean you ought to mind everything you read. While there’s lots of good advice in circulation, some of it is outdated — or just flat out wrong.
For instance:
* Regular Tune-ups Will Save You Gas
Most new cars — indeed, most cars built during the past decade — do not need regular tune-ups of any sort. Spark plugs last as long as 100,000 miles; ignition systems are largely maintenance-free and the car’s onboard computer makes regular adjustments automatically to assure peak performance — and economy. Unless the “check engine” light comes on, you should not worry about tune-ups until the time/mileage interval specified in your owner’s manual.
* Warm Up Your Car Before You Drive Off
In the days when cars were fed fuel by carburetors (and took several minutes to reach normal operating temperature) this was a good rule to follow. But cars haven’t come with carbs since the late 1980s — and a modern car reaches normal operating temperature within moments of start-up. “Warming it up” only wastes fuel (as well as time). in fact, prolonged idling may be harmful to the vehicle as it actually delays full warm-up, which can increase wear and tear. The right thing to do is to start the car — and drive it.
* Shut Off Your Engine If You Expect To Be Idling For More Than 30 Seconds Or So
Hybrids save gas by shutting down the gas half of the gas-electric powertrains when the car comes to a stop. You can do the same thing without all the high-tech assistance of a computer — or the expense of buying a new Prius. Just turn the engine off when you hit a red light — or find yourself stuck in traffic. You can reduce your overall fuel consumption by as much as 5 percent this way. Just be aware that you may reduce the life of your starter motor — and you’re working your car’s battery harder than you otherwise would, which could and probably will mean it dies sooner than it otherwise would have.
* Don’t Run Your AC; Roll Down Your Windows Instead
This is a “maybe yes, maybe no” fuel saving suggestion. Older vehicles — generally, those built prior to the mid-1980s — had AC systems that were very power hungry, with huge compressors that took a lot of energy to drive them. If you’ve driven such a car, you may recall actually feeling the load on the engine when the AC was turned on. If you have one of these old cars, you can indeed save some gas by limiting the use of your AC. But with modern cars, the potential fuel savings are lower because the AC systems in modern cars are much more efficient. They don’t load the engine nearly as much — and you might actually end up burning more fuel by rolling down the windows and increasing the car’s aerodynamic drag. Rule of thumb: If your car is a 1990 model or newer, running the AC probably won’t increase your fuel consumption much — if it’s even noticeable at all.
* Keep Your Car Washed And Waxed
Some people believe a clean car drives better than a dirty one — and they may be on to something. A smooth, clean surface cuts through the wind more efficiently than a bumpy lumpy one. Increased wind resistance means higher fuel bills — though the increase is probably very small, for the most part. With one exception: If you have a truck or SUV and have taken it off-roading, caked-on mud clinging to the undercarriage and fenderwells can add a surprising amount of weight to the vehicle — as well as increase drag. A session with a power washer can get your fuel bills back to where they ought to be.
* Using Lower-cost “Regular” Gas To Save Money
This is fine, if your vehicle was designed to burn regular unleaded. If, however, you happen to own a vehicle designed to run on high-octane premium fuel, filling up with regular is a bad idea because your engine’s efficiency will be reduced - and you’ll probably end up getting worse gas mileage, as well as reduced performance. To maximize the fuel economy potential of any engine, it is important to use the type of fuel it was designed to burn — whether that fuel is 87 octane regular or 93 octane premium. It’s just as counterproductive, incidentally, to burn premium gas in an engine built to run on regular. You won’t get more performance — and you may see a mileage loss — as well as the loss you’ll pay up front for buying the higher-cost premium fuel.
Comments?
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19 Responses to “Truth And Lies About Fuel Saving Tips”
By Hubcap on Sep 11, 2008
HalHayseed, Since most of the gasoline you buy is stored in a double-walled underground tank, I don’t think the temprature variation is significant even if there is one.
Once it’s in your car though, it’s a different story. When I was a kid, my dad filled up his Dodge van on a very cold Denver day and then parked it in our heated garage.
The next morning the garage was submerged in about an inch of gasoline. It’s a miracle we didn’t have a fire!
By steve on Sep 10, 2008
I was in Brazil and noticed that some of the lights had counters as well, and after 10PM the stop light cameras turn off so you don’t need to stop if you don’t have to, more like a yield. Very different compared to here in the U.S.
By vwfarm on Sep 10, 2008
When I was in Bangalore, India, the red lights have counters on the them so you know how long it (in seconds) will be between red to green lights. Just about everyone turns off their motors (motorcycles, cars, truck & buses) on every red light.
By HalHayseed on Sep 9, 2008
Can anyone verify or disprove the notion that it is more cost-effective to buy your gas when the temperature is cooler?
The hypothesis is that gasoline, being highly volatile, expands and contracts to a high degree with temperature fluctuations, and so is denser — will weigh more per volume — when it’s cooler.
Since it’s bought by volume, you get more (by weight) for your money if you buy at night (or whenever it cools down in your area). Or so goes the hypothesis.
It seems to make sense to me; does anyone know for sure?
By Jeff on Sep 8, 2008
I don’t get the connection between drag resistance and a Piper. Drag and lift are 2 different aerodynamic principles.
By Philscbx on Sep 8, 2008
Yes, it’s possible to shut down the engine at long lights when you know most of them. Some are very long. You just don’t want to be first in line at the light. Being in 5th position or more gives you plenty of time for restart.
But as one person posted, NO, you don’t lock the ignition and steering, Key is left on, engine off. Use Neutral for automatics for Quick restart so it’s not locked in park where you need to apply brakes to unlock shifter, and manuals left in gear so only depress of clutch for ready to roll out when started. This is a major advantage for those with electric cooling fans. Vehicles with electric fans during hot stops while engine is off is win win deal.
I watch the digital temp gauge drop (with engine off) 50 degrees vs increase 50 degrees from heat soak with electric fans on. Heat soak from exhaust system manifolds at 1200 degrees can damage engine control sensors, plastic, hoses, wiring gets brittle, or loss of coolant at overflow, etc.
2 or more minutes with engine off isn’t going to drain a good battery. High battery load items: interior heating/cooling system fans, Head lights, Engine Cooling fans. Turn parking lights on if in line, at drive through’.
Low Load Items: Stock radio’s do not take any power. No gain turning them off.
Myself, I added a manual radiator fan switch to cool down engine and coolant during long stops vs letting system max out to turn them on.
Most blown head gaskets on aluminum blocks are from overheating from repeated overheating overflows of small amounts till it gets air ingested creating hot spots.
The people with turbo chargers know the routine with cool down procedures before shutting down an engine to prevent damaging heatsoak. Inspection of radiators is more critical now as they are designed to work right to the edge when new. Any build up inside will kill your chances of survival.
You’ll notice in the Southern high heat belt, that squad cars left running controlling traffic will open hood to prevent overheating and damaging heat soak.
I do the same for years even pulling in to get fuel. Coolant is right at 200 degrees, and on a 100 degree day, it needs all the help it can get.
You’ll notice air drag is at prime right at the edge at 50 mph. So if you can take advantage of this speed w/o creating havoc, you win.
I cruise in 2nd if under 33 mph to maintain a controlling attitude for slowing and speeding up.
Any speed above 50 is dramatic drag resistance.
A standard Piper can lift off the runway at 65 -75 mph. Test with hand out the window.
You know your in the wrong gear if you cannot speed up at will w/o downshifting a stick manual. This hammers the engines rod and crank bearings when in the wrong gear. There is less oil pressure to help offset this torture.
Cruising in high at lower speed is fine if it’s basically coasting with no load.
I leave automatic out of over drive till up to freeway speed. Constant unlocking from slight stepping on fuel while in slow city traffic of torque convertor is the number one cause of tranny damage.
See all the cars lined up at the tranny shops?
Practice these steps in quiet areas of traffic before getting into real rush hour.
By Hubcap on Sep 5, 2008
Randy, I very rarely seem to be in a situation where I know how much longer before the light changes.
The other thing is the impatient people. I usually sit at a light with the trans in neutral and the clutch out. I think it reduces wear on the TO bearing…but that’s just me.
Just this morning at the very first light–one block from my house–in the instant it takes me to stomp on the clutch and shove it into first when the light goes green, the guy behind me was honking.
If I took another two seconds to restart the engine, he’d be out of his vehicle using a tire iron on my windshield!
I know, screw ‘em; but it’s just not something I’m comfortable with.
By George on Sep 5, 2008
link
http://www.caranddriver.com/features/columns/c_d_staff/larry_webster/driving_for_fuel_economy_column
By George on Sep 5, 2008
In the August ‘06 Car and Driver
They tested a BMW 330i stick
75mph in 6th, 29.7
75 in 4th, 26.4mpg
By George on Sep 5, 2008
Randy, what kind of EGR does your Focus have?
By Randy on Sep 5, 2008
Jeff to expand on what you said:
With a manual transmission you can come close to 25 mph in many cars. I can easily stay at 30 mph in my vehicle and have been down to around 25 mph. The big thing if you go that slow you want to stay away from trying to accelerate much at that speed and gear and you can not do it on an up hill. If a road is flat and you are not around any traffic you can go very slow in high gear because there is very little wind and rolling resistance. My best milage tested was between 30 mph and 35 mph.
By Randy on Sep 5, 2008
Hubcap the largest decision on if you should shut the car off at a stop light is how long the light is. Some are less than 30 seconds and some are 2 minutes or more depending on turn lights and amounts of traffic. For long stop lights it makes sense to turn off any car as long as it has no problems starting.
By Hubcap on Sep 5, 2008
Doug on Sep 5, 2008 writes
“When the car comes to a stop and the clutch pedal is not depressed, the engine shuts off.”
My experience is that every manual transmission-equipped vehicle will behave that way, sometimes rather violently. LOL!
But I get what you’re saying and it certainly does save fuel in car that is designed to do that.
By Doug on Sep 5, 2008
The Mini Coopers here in Germany have a Start-Stop Function as standard equipment. When the car comes to a stop and the clutch pedal is not depressed, the engine shuts off. When the Accelerator is depressed, the motor starts. In the EC standard fuel consumption test, the car saves ca. 0,5 Liters/100Km.
By Jeff on Sep 4, 2008
Driving slower does not always equate to better gas mileage. Driving too slow in a particular gear (bogging the engine) is not the most efficient mode of travel. That is why it is silly to try to drive 25mph in top gear in a vehicle with a manual transmission. You also have to look at where the engine develops peak torque. A Corvette can get the same, or better, gas mileage at freeway speeds as a smaller vehicle with a smaller engine. Vehicle weight is also a huge factor. The simplest way to increase gas mileage while maintaining a certain level of performance is to reduce weight.
By Hubcap on Sep 4, 2008
I’ve always questioned the shutting off the engine at lights thing.
On the restart, the fuel goes rich, even if it’s just for an instant. So I wonder if there is more fuel used by restarting then would be if the engine were left idling.
Secondly all the electrical accessories that are running continue to draw on the battery.
Then the additional battery draw from the restart coupled with the computer now having to readjust to a hot-soak-restart strategy and the alternator drawing additional power to re-charge the battery.
After all that, you’ve saved what, half a thimble of fuel?
Consider also the safety aspect. With the engine off, you’ve lost power steering and brakes; you may not be able roll your windows up or down, and depending on the vehicle, you may have locked the steering column. And if you find yourself needing to move quickly–maybe because of an approaching emergency vehicle–you’re screwed.
I’m going to say this one is not worth the savings.
By Highway on Sep 4, 2008
To expand a bit on Todd’s answer, it’s difficult to say what the most efficient operating regime for a vehicle is because it varies with so many factors.
The primary one is vehicle shape and drag. I believe that as Cd’s have gone down, the speed at which you ‘break even’ and make maximum efficiency has gone up. 20 years ago, this speed was about 40 mph. The last figure I heard in passing was just over 50 mph, for an ‘average’ vehicle.
The reasoning is that as speed increases, the aero drag force becomes the dominant force requiring power to overcome. For those who watch Top Gear, this was mentioned in one review, might have been when May drove the Veyron to 255 MPH, as saying something like it takes 150 horsepower to go 100 MPH, but then it takes another 500 horsepower to go up to 200 mph (paraphrased, I don’t remember actual numbers, but were in this ballpark).
So with aero drag such an important part, it’s very hard to say anything like Hal Rounds is asking. You can say that 45 in 4th will be more efficient than 45 in 2nd. You can say that max gear is more efficient than any other gear. But comparing on opposite sides of the max efficiency point just can’t be done without specific experimentation.
By Todd on Sep 4, 2008
To: Hal Rounds
I am no expert but I’ll try to answer your question to the best of my ability. First I don’t know of any study that compares fuel efficiency, second if you are driving your car at 45 mph while in 2nd you are reving the hell out of your motor which will result in lower MPG. If you are going 60 MPH in 4nd you are reving your motor to a minimal and will result in OK MPG. Third if you have a big motor that will most likely burn more fuel but if you have a smaller motor with a turbo and more gears with better ratios that would also result in better MPG because you can be driving at a faster speed and be in top gear while reving your car to a minimal. This however can vary depending on the vehicle you have. I hope I answer some of your questions.
P.S. Sorry if it was not detailed enough to your expectations
By Hal Rounds on Sep 3, 2008
Is there a study that compares the fuel efficiency of a car at speeds depending on which gear is being used? Is it not true that a car going 45 in 2nd is burning more per mile, say, than one going 60 in 4th?
Does it not depend on the individual car and its power train - engine volume and final gear ratio?