Didn’t I hear somewhere that shifting into neutral gear when you go downhill saves gas? (If so, why didn’t I hear that it makes the computer go kerfluey in a car with automatic transmission…or DID it?) My 2007 Corolla’s computer had to be replaced after weird death-gasps, and I’m wondering if I hastened it to an untimely demise by coasting down the hills and dales. I made it all the way from the Green Mountains down to Massachusetts in neutral (well, almost). I’m sure an NPR listener offered this as a “green tip.” No?
Your engine is still connected to the transmission whether you’re in neutral or drive. Just keep it in drive and ignore goofy tips like this. In fact even if there was a chance that fuel savings could be realized here they would be so miniscule that you wouldn’t even be able to reliably observe it. You’ll see more benefit from properly inflated low-rolling resistance tires and a gentle right foot.
Absolutely goofy. It’s unsafe, and may actually use more gas (by keeping the engine running in neutral, as opposed to having the engine spun at a higher speed in gear with the injectors shut off for some cars). Your efforts will be paid off 100 times more by careful use of the gas and brakes.
Green? No. Goofy? Perhaps. DANGEROUS? Definitely, yes!
Coasting downhill in neutral is not safe, and it saves ZERO gas. If your foot is off the gas pedal, the engine is getting only enough gas to maintain idle, no matter how fast the car is going.
Coasting did not cause the computer to fail.
Just think of all that gas you’re saving by not driving it because the ECU blew up. 
IF you save ANY gas, it’ll be about a half teaspoon per tank. Compare the cost of that to the cost of that ECU you just replaced
Depending on the car, in some cars you may gain a little mileage by doing it, in others you will loose some mileage by doing it. In any case the difference is small and it also depends on the car, the speed, the grade of the hill the length of the grade the speed limit, the traffic etc. Don’t bother.
While I have not researched it, I suspect all that in and out of gear is not going to do the mechanics of the transmission any good. (Transman, care to comment). Transmissions are expensive.
Computer: No it will not damage the computer. It may cause some minor problems with adaptive systems, but that would not damage the computer nor would it likely cause any serious problmes.
Many states is it is actually illegal to perform this.
The biggest problem here is that when you say “coasting in neutral” nearly everybody on this board assumes you are talking about freewheeling down some really long and steep mountain road and gives an answer based on that assumption. If I find myself in that situation, I keep my car in gear and let the DFCO feature cut off all fuel use. Ditto for approaching a red light when I have so much speed that I have to brake anyway, sometimes I even downshift to keep the car in DFCO longer.
My commute to work is filled with dozens of, oh, let’s not call them hills, let’s call them coasting opportunities. These are grades so mild that you don’t need to use your brakes when you freewheel down them. What happens when you keep your car in gear? DFCO does not come into the picture because if you take your foot off the gas, the engine braking slows you down and you need to re-accelerate. What happens is that you have to hold a small amount of throttle just so the engine will let the car coast. The fuel use difference is the difference between idle and a 3000 rpm fast idle. A Honda Fit uses about .3 gallons per hour idling, triple that idle speed and the fuel burn will be about triple the idle fuel burn.
Is it illegal? Cool! Another good reason to do it! Stick it to the man!
Does it save only a “teaspoon” of gas? My last tank yielded 46 mpg. How’s your gas mileage?
Goofy and dangerous
I do not want to start a new blaze about saving gas versus dangerous driving, but — in a country like Denmark where I live(highest point, all of 600 feet above sea-level) you ain’t gonna see any big danger levels. I have driven my 1995 Citroen ZX 1,4 monopoint injection over 600 miles as recommended here on this forum - that means no freewheeling under any circumstances, just letting the engine slow it down. Ended up with: 35,8 mpg. The next 610 miles: Coasting at any place possible comming up to turns, junctions, downhills etc. without slowing down other traffic. This time: 42,95 mpg.
Make your own decisions, but remember that if You are coasting down a mountain, You take other lifes in Your hands than Your own. Do You believe that that’s worth two ounzes of gas.
Best regards
Klaus
Klaus
Regarding: “Do You believe that that’s worth two ounzes of gas.”
In the US, there are apparently people who do believe that endangering the lives of others is worth 2 ounces of gas. Isn’t that sad?
But, then again, this is a nation where many people seem to think that the ability to “gut” a moose qualifies one for the office of Vice-President of The U.S. That is even sadder, I think.
We live in a very strange world.
Hi VDCdriver
YES, it is a very strange world we are living in.
People don’t mind becomming thieves for some stupid 10 gallons of gas (allthough at 8,36 dollar a gallon), The government don’t mind old people dying of lack of care and so it goes on. Don’t even for a minute think that Your government is worser than mine. Though, I still relish the good memories of those wonderfull friends I got through my 19 months in California. You can still be proud of Your nation.
Best regards
Klaus
Saving two ounces of gas? Redo your math! 610 miles at 35.8 mpg is 17.04 gallons of gas. 610 miles at 42.95 mpg is 14.2 gallons of gas. Drive the car 100,000 miles and the difference is 465 gallons which would cost about $1700 in the US.
How did the freewheeling trip go? Was it really a white-knuckle ride with the car just barely in control or did the steering wheel and brakes still work? How long did it take to get the car back in gear for all those times you needed to do all of those unexpected emergency accelerations? Actually if that is a concern, you can freewheel in fourth or third with the clutch disengaged and have maximum acceleration available faster than someone who is driving in fifth can downshift. And remember, I’m talking about coasting down mild grades here, not freewheeling down Pike’s Peak.
Now let’s talk about goofy. How many people go to the ends of the earth, visiting every dealer in a 50 mile radius and negotiating for weeks to get $500 better deal on a new car yet won’t lift a finger even trying to change their driving habits to save literally thousands of dollars if fuel over the life of the car.
While not a direct response . . . on a related topic . . . didn’t SAAB even offer a “freewheeling” transmission and encourage drivers of the old 93’s and 95’s (no, not the current yuppy-puppy GM 93’s or 95’s, the originals)??? I personally don’t draft or hyper-mile, but since I drive a lot of the same roads daily here in the Pocono mountains of PA, I know when/where I can shift into neutral on some grades, but I don’t see anything wrong with neutral with my old Honda, the idle drops to 750 from 3000 and I don’t exceed the posted speed limit, watch my braking and stuff like that. Rocketman
Yes, you are correct. The old Saabs of the '50s and '60s did have free-wheeling, but that feature could be locked out if the driver so desired. Those early little Saabs also featured 2-cycle engines and “four on the tree” shifting. How’s that for odd-ball?
The first Saab designs (both engine and transmission) were derived from the German DKW, which was a part of Auto Union (DKW, Horch, Audi, Wanderer). After those other makes ceased to exist, Audi began to use the old Auto Union symbol–four interlinked rings–which was supposed to represent the four independent makes that had been joined together in the '30s to form Auto Union.
Why would it be illegal to COAST downhill in neutral? I recall the issue has to do with large trucks coasting to such high speeds that they lose control. The law concerned manual transmissions and long downhill grades. Coasting down one long incline to gain enough speed to carry the truck up the approaching hill at enough speed to be able to climb it at a reasonable speed enabled trucks to get through mountainous terain without slowing to walking speed in ‘double low.’ Neutral coasting was called GEORGIA OVERDRIVE many years ago. It was dangerous. The law has nothing to do with automobiles with automatic transmissions, but, of course, TECHNICALLY, if the laws are on the books, drivers may be cited.
I thought so . . . I remember reading an article on the old SAABs and remember the 2 stroke, the aircraft design, the lightweight aspect of the car . . . even that the color choice was limited to keep the price down. Gotta find that article . . . I’ll post it if I can find it. Thanks VDC! Rocketman
The very early Saabs had a 2 cylinder, 2-cycle engine, and after a couple of years, it was altered to a 3 cylinder, 2-cycle design. Post-war Europeans were very cash-poor, and this was just one of the many cars that were originally designed for both low fuel consumption and a low purchase price.
Goofy, Dangerous and Illegal in many states!!