This past weekend I took a road trip with a rental car. I had a 2010 Dodge Avenger and going down I averaged about 70-75mph and got about 30 mph, coming back I bumped my speed up to about 79-83 and saw the gas mileage dip a bit. So how do you know what speed (avg) wise while on the freeway to drive to maximize your fuel consumption? Also what can you do while driving to maximize it? Going down I didn’t have any windows open due to some rain, and didn’t run my AC just vent air. Coming back had the window open a bit and some vent air.
The EPA tests highway at about 55 mpg (see attached chart). Manufacturers generally design the vehicles to do well on the EPA tests, so I guess the maximum could be gotten at about 55. At least until that big logging truck behind you runs you off the highway. And he will.
http://www.fueleconomy.gov/feg/fe_test_schedules.shtml
But you changed two things during your test trip: your aerodynamics and your direction. Airspeed differs depending on where the wind is hitting you from. A change in the weather may have influenced the readings too. Barometric pressure and hygrometer readings count also. The higher the air pressure and/or the higher the humidity is the more resistance your car has to overcome.
The things you can do to maximize it?
Drive conservatively. No stoplight drag racing.
Keep a steady speed on the highway.
Keep the vehicle well maintained.
check the tire pressure regularly.
Dump the junk in the trunk. Mother-in-law’s old storage trunk costs money to haul around.
Large throttle opening + low engine speed = less pumping losses = more efficiency.
Large throttle opening + low engine speed = less pumping losses = more efficiency.
In this case “more efficiency” means the engine is able to produce more power for a given amount of fuel. But in no way does that translate into better gas mileage.
The more the throttle is open, the more power output the engine is being asked to deliver. It produces that power “more efficiently” than at partial throttle, but it has to consume more fuel to do that.
On a related note, a second but very important reason an engine operates more efficiently at full throttle is because of the “denser” mixture - and all the efficiencies of faster combustion associated with that.
If the car has a tachometer, get into overdrive and run it around 1800 - 2000 RPMs. On my Accord, that’s about 55 MPH.
I did a test several years ago with a rental Impala. I drove from the Orlando Airport to Cocoa Beach at 70 MPH, then drove back at the end of my trip at 60 MPH. I used cruise control to keep the speed constant. It used more fuel at 70 than at 60.
It’s pretty simple: on the highway, the faster you drive, the more gas you use.
Pushing a car through the air becomes increasingly more difficult as speed rises.
There’s no way to get around it. Increased speed requires more power, which translates to higher fuel consumption, which translates to lower fuel mileage.
If you want maximize highway mileage, drive at the legal limit.
In my experience, you’ll be one of the very few.
“How do you get your best gas mileage”?
Slow down. 55-60 mph is the best fuel economy for most passenger cars and trucks. Just be prepared for the horns, fingers, and tractor-trailers blowing past you.
Acceleration and braking are the two things that really effect fuel mileage…You want to minimize both…As you push the speed above 50MPH aerodynamic drag plays a bigger and bigger role in limiting fuel mileage…
Professional drivers who are driving to achieve maximum fuel mileage and nothing else can achieve stunning mileage numbers…
I get my best mileage by driving as if my brakes don’t work.
Increasing speed hurts mpg on any car at any speed. So, you pay a price for getting somewhere faster by using more gas for the trip. Most interstates where I drive in PA are 65 mph roads, so I go 65. I’d get about 15% less mpg by pushing the speed up to 75 mpg. I use cruise control so that my 65 mph is steady. This might not be the best way to get more mpg, but steady speeds are good for mpg. If you really want to get max mpg you let the car go faster downhill, up to 75 mph and then let is slow going uphill to about 55 mph. Your overall travel time will be the same but you’ll use less gas going up the hills.
Around town driving it is a matter of planning your trips to be more efficient and going light on gas for accelerating and light on the brakes for stopping. This way you’ll coast a bit more which is good for mpg.
Keep the car maintained well, tire pressure up, and drive with a soft touch on the pedal.
I do respectfully disagree that higher speeds always translate to lower MPG. That would depend on the car, engine, and gear ratios. My Lincoln gets better fuel economy (about 1.5 on average) at 65-70 than it does at 55. Due to the V-8 and gear ratio 55 on that car is lugging so kicking it up a bit faster seems to make it breathe a bit easier.
If the bulk of my driving was city then I’d seriously consider a rear axle ring/pinion gear change to a 3:73 or 4:10 gearset because low speed city driving is a bit irritating due to the lugging.
B.L.E; me too, I have my built in Prius-regenerating energy from braking. I know every time I hit the brake I am wasting gas, so I pace myself so that I don’t need brakes much. I just changed the pads on my Camry after 40K miles and they had half the material on them.
I know it’s just anecdotal evidence, but I do tend to get better fuel mileage using the more throttle/lower engine speed method. My daily driver is Mustang GT with a supercharger, 4.10 gears, with a manual transmission. It may be possible that the technique may be more effective on relatively powerful car with a relatively high degree of mechanical advantage via the shorter gearing, as the throttle doesn’t have to be held open that long even at lower revs to get up to speed. Versus a heavier car with less power and taller gearing.
Although driving 55-60 MPH will maximize your highway fuel economy, I suggest it is more practical (and safe) to set your cruise control on the speed limit to maximize fuel economy. If your fuel economy with the cruise control set at 70 MPH is too low for your tolerance (or your budget), it’s because of what you are driving, not how you are driving.
You start with a high mileage vehicle to begin with. Then you use most of the advice given above. One exception, don’t use cruise control. It is constant load, not constant speed that is most efficient, but there may be some credibility of accelerating to some upper limit speed and coasting for awhile on fuel injected cars. That is how most birds fly by the way.
OK4450, if your Lincoln Mark VIII still has its original air suspension, the car lowers itself about 2" at speeds above 65 mph, reducing its aerodynamic drag. That was, I feel, the most underrated car of its time. It was a great car.
@FoDaddy
I don’t doubt you have a driving habit that gives you better gas mileage than other driving habits.
When you’re cruising down the road at 55 mph, your engine only needs to produce about 12 hp to sustain the vehicle speed. To do that, your foot will barely be on the accelerator, your throttle plate will be largely closed, and your engine efficiency will be quite low. However, your MPG will be quite high. If you accelerate harder, your engine will operate more efficiently (doing more work per unit of heat/fuel) but your gas mileage will fall.
I don’t have my notes or book anymore from my Internal Combustion Engines class, but here’s one link I found that might explain it better:
http://www.viragotech.com/fixit/FuelEconomyEngineEfficiencyPower.html
The speed limits on the freeways I drove on this past weekend on average were 70 mph so I usually stayed within 10 mph of that or around 79 mph. And at that speed I was getting blown off the road in many cases by other cars flying by. I always use the cruise control when on the freeway.
Also I came across a gas station where when you put in gas you could “select” to have a “special” additive put in while fueling at a “small” additional cost of $6.96. I have never seen this included in the pumps before. How can anyone believe it will help?
It’s a rip-off (the fuel additive at the pump). In fact, when it’s sold in a pump instead of a bottle, how do you even know they are putting it in there?
As to keith’s remark about cruise control, he’s right that a throttle lock (like the ones used on motorcycles) would save more fuel than cruise control, but it’s been proven, repeatedly, that cruise control saves fuel when compared to manually operating the throttle. Of course there are exceptions. If you are driving a heavy vehicle, or through hilly terrain, you can save fuel by decelerating while going uphill, and accelerating while going downhill. However, on a normal car, traveling over flat terrain, cruise control beats manual control every time.
I’ve heard keeping your vehicle clean and waxed can make a difference.
Anyone know if there’s any truth to this?
It’s a myth. It’s something you tell your kids when they argue with you about not wanting to wash and wax the car.