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"Hypermiling" in an automatic?

I live in a rural hilly area and have often shifted my car into neutral going downhill – I’ve got it down to where I can maintain a reasonable speed. I used to have a standard shift, but have an automatic now and a friend told me that I’ll torch the transmission by letting the vehicle run in neutral.
Is that true?

If you drop it into gear without the car being stopped, it’s not very good for it.

But, you’re wasting fuel. Modern cars shut off fuel delivery to the cylinders when you’re going down hill because gravity is enough to keep the engine turning. Putting the car in neutral means the engine needs fuel to keep running.

Like shadowfax said, you are actually using more fuel doing that, plus it is at least slightly dangerous.

This has been discussed many, many times here. Please search for those threads and read them. The bottom line is that it’s slightly less safe, it’s possibly illegal in your state, and it probably uses more fuel instead of less.

Thanks for the summary @lion9car. Modern transmissions have fool proof computer monitored accidental excursions into the idiot range…you probably won’t damage a thing shifting it manually.

+1 for lion9car. Shifting into neutral is not a safe thing to do and does not save fuel.

I’m going to start a new trend for hypo-miling. I’m going to first install a binary gas pedal, completely deflate all my tires, strap a 4x8 sheet of plywood to the grille, festoon the exterior with cube shaped side view mirrors and leave it idle overnight so it’s warm in the morning when I get up. Oh yeah, I also want to install an array of ceramic, wirewound resistors on the roof to dissipate all the unused energy from the alternator into the atmosphere…if you have any other great ideas on how I can minimize my mileage, please advise…

What little money you may save in fuel, you will more than make it up in transmission repair.

“if you have any other great ideas on how I can minimize my mileage”

Disconnect as many spark plugs as will allow the engine to continue running.
Remove the thermostat.
Fill the oil sump with 90W-140 gear oil.
Fill the trunk with sandbags.
Strap a bungee cord to the brake pedal so they’re always dragging a little.
Punch a small pinhole in the gas tank (always park on an uphill slope).
Fix the steering wheel to full left lock with bungee cords so you go in circles and never get anywhere.
[This was fun!]

Shadowfox, You are correct about gravity keeping most engines running on a downhill, but Transman and I had a long argument about that some time back…He said that the transmission would not keep the engine turning or hold back the vehicle going downhill. I argued that it would, I know it would. I have turned off the ignition and turned it back on 45 seconds and it fired right up. I tried thiis more than twice. He acted like I was a lunitic and didn’t know anything about cars.
Now, I realize that not all cars are created equal.

Let it go, man. Let it go.

Here’s another “hypomiling” tip: when replacing a clutch master cylinder…if you damage the clutch interlock safety switch in the repair, just jam a popsicle stick in it and keep going.

(This will convince the computer you’re always pushing the clutch in, thus eliminating any perky “fuel shut-off.” Also, you can start the with gear engaged, which might be a hazard if your IQ < 20 :wink:


He said that the transmission would not keep the engine turning or hold back the vehicle going downhill.

Honestly, having seen @Transman’s posts for however many years we’ve been around here, I have trouble believing that he would contradict himself in the same sentence. I’d have to see the original post, or hear from him, before judging. At any rate, I have no doubt that he’d agree that a vehicle which is already going over 30mph is not going to instantly stop when you take your foot off the gas. As such, the inertia of the car will keep it moving forward, and because the wheels are still turning, the engine will still turn - unless you put it in neutral.

Your post also seems to indicate a bit of confusion as to the scenario - we aren’t talking about turning the key to off here - just about coasting down hill either in gear or out of gear.

We, Whitey, It hurts to have someone to treat you like an idiot, when you have just proved HIM wrong! And folks like yourself, defend HIM.

So, Elly, you’re offended that I’m defending him, even though I haven’t done so? That speaks volumes.

I guess now there is no reason for me to remain neutral.

Transman is a master technician who has been rebuilding transmissions for decades. What, exactly, are your qualifications?

I’m not saying Transman is never wrong, and I’ve yet to read the argument you referenced. I can say, from experience, that Transman has made significant contributions to this forum. I struggle to find as notable contributions from you. So forgive me for taking his side now that you have accused me of doing so. I would have never dared to do such a thing otherwise, especially without reading the discussion in question.

BTW, if Transman had been the one to bring this silly argument from one thread to another, indicating how bitter he was, I would have given him the same advice. Let it go, man.

The argument started when Transman said that an automatic transmission would not hold back a car going downhill. I said it would and he proceded to tell me about his many years of experience. So I tried it and to prove that the engine would be turning, I turned off the ignition and as I approached the bottom og the hill, I turned it on and the engine was running. I tried it 3 times with the same results. He told that I didn’t know what I was talking about, and several “experts” agreed with him . Whitey, if you weren’t one that defended him, forgive me, it has been quite a while
Shadowfox, I never said that a car would stop in its tracks if you let up on the gas, as you mentioned. and you said “unless you put it in neutral” In which case the engine would still run as long as you “never turned off the ignition”.

More hypo-miling tips:

-Disconnect both O2 sensors.
-Store towels in your air intake-you never know when you’re going to the beach!
-Drive around in 1st gear (or low range, if so equipped.
-Tow a second car behind you, just in case the first breaks down or runs out of gas.
-Crank your A/C to max and run a small space heater off the cigarette lighter-see which wins!

Just take out one of your half shaft and you will be hypomiling in no time