I agree with many previous posts, but want to mention “short shifting” a manual transmission. Fuel mileage on my '92 Accord, 5 speed manual, increased from about 28 mpg to 29.5 mpg when I began upshifting at 2500 rpm. Previously I had upshifted at 3000 to 3500 rpm. The improved mileage is due to using increased throttle positions in higher gears (reduced pumping losses as previously mentioned). I drive the same roads to and from work every day. Definitely comparable conditions before and after using “short shifting” technique. Tough to do this in an automatic, however.
I’m sure you will get better gas mileage at 70 than 80, an most cars will get better mileage at 60 than 70. Just stay to the right and others will pass you. The faster they are gone, the less dangerous they are to you. I’d say go the speed limit as a compromise between mileage and safety.
I’ve done short shifting like @lars46. '81, '88 Accords and the 2006 Matrix, all 5-speeds.
Shifting at 2000-2500 on flat ground & gentle acceleration.
Besides reducing pumping losses there’s less loss from engine friction.
Wow, $6.95. I have heard that some pumps are now giving the option to put in an additive based on a price per gallon, not a fixed price. The local Costco has added the tanks to do this but I was told it would be free. (Yeah free, figure the odds?)
edit: Not all Costco’s are doing this. It is up to local management.
“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.”
A well designed gasoline engine will consume about 0.45 pounds of gasoline per horsepower hour at peak torque. If an engine could maintain that efficiency when it’s throttled down to 12 horsepower, the engine would burn 5.4 pounds per hour or about 0.9 gallons per hour which at 55 mph would come out to about 61 mpg.
A car gets good gas mileage at 55 not because it’s efficient but because it takes so little power to go that slow. Most sixes and V-8s are grotesquely inefficient when they are only making 12 horspower.
Just to add a little, few cars display the true speed. Nearly all cars will display a higher speed than your car is really going (like 5%). If you have a GPS and it displays speed, it likely will be displaying a very accurate speed. (maybe a little off when you are driving hills) it depends on the unit. So when that truck wants to pass you and your speedometer reads the posted speed limit, you may really be under the speed limit.
If you are looking for the best MPG and you are driving hills, things really get complex when you need to also factor in the road's grade.
I like to get the best mileage, even when it cost me a little effort and or time, but I try to do it without delaying anyone else. I like to drive safe and if I am delaying another driver, means they may be aggravated and less safe.Cruise control can save you a lot of gas in flat terrain, which is why I almost never use it, because it’s mostly hills where I live.
BTW, I’ve always heard that the optimal speed for fuel efficiency is 58 mph, but some people say it’s 85–120 mph saves a lot more gas, because once you get killed in auto accident, you won’t use anymore gas at all.
Uncle Turbo- You will get better gas mileage lettin the car gather speed downhill and lose speed uphill but going down at 75 and up at 65 won’t average 65 because you will spend more TIME at the lower speed.
Some decades ago (I simply do not remember exactly when) a car magazine did some strange tests. To keep rpm down and throttle open to reduce engine speeds while eliminating pumping losses, they (with a manual transmission, of course) would keep it in high gear, hold the throttle wide open, then when the car got to like 30 or 40 mph, I don’t remember, push in the clutch, and turn off the key, then let it slow down to like 15 to 20 mph. (Again I don’t exactly remember). Then, turn the key on, and pop the clutch to start the motor again.
I can imagine what the engine sounded like with the throttle wide open at 15 mph in high gear. But, they got some ridiculous mileage, again by bad memory, like 40 mpg or 60 or some such number.
This is not a practical way to drive, they did it as an exercise and to demonstrate certain issues in engine design.
Does anyone else remember this?
Having re-learned how to ride a bike in recent years, I am made aware of how it pays to be thoughtful of all that is around me when pedaling. Every effort must be made to keep the speed as constant as possible. Avoid stopping, speed down one hill to enable ascending the next hill more easily, use the appropriate gear, avoid congestion and keep the tires fully inflated. All that applies to physical economy in bicycling applies to operating economy in driving.