Pulse and Glide with an auto trans - Fuel Economy, Hypermiling, EcoModding News and Forum

Hermie · 11-04-2009, 06:38 PM

I was curious- Is it mechanically safe to pulse and glide in a non-hybrid, automatic transmission car?

Will going from Neutral to Drive at speed harm anything, or re-engaging into gear at speed do any damage to the transmission?

Christ · 11-04-2009, 07:32 PM

I EOC in my van, so does orange4boy. Neither of us have seen any problems, and I go much further than he claims to.

In fact, I've gone up to 3 miles at 60 MPH in neutral w/ the engine off.

When you're at speed, you can put the transmission in neutral, but every time I tried something like that, I didn't really find any gains, because the same places that I put the engine in neutral are the places I'd normally be letting off the accelerator anyway, which meant that in most cases, the engine was basically at high idle, not loaded, so fuel savings were nil.

EOC, I like to think I'm seeing an increase, but I'm coasting down more than a few MPH before starting the engine, as well. I don't do too much driving where I'm going less than 45MPH, so my gains are limited by speed and aerodynamics. In town, you can coast alot further per MPH lost on average, so you may see larger gains than I would.

99LeCouch · 11-04-2009, 08:17 PM

I can see small gains on the highway by putting it in N going down large hills steep enough to maintain speed down. It's good for 0.5-1 mpg with my car. Letting my foot off the gas is almost as good.

wagonman76 · 11-05-2009, 01:46 PM

Depends on the transmission. Mine don't re-engage very nicely at anything above 25 mph. Some other vehicle transmissions it does it just fine.

srortega · 11-05-2009, 01:57 PM

My 4Runner goes in and out of N smoothly at highway speeds.

Hermie · 11-05-2009, 04:09 PM

In other words, not really enough to make a difference or outweigh the risk of going past N and into R, which will pretty much kill the car. Alrighty, thanks! ^^

srortega · 11-05-2009, 05:19 PM

If your selector allows you to go past neutral, then no not worth the risk. In my car I don't need to push the button to go from drive to neutral and it will not allow me to go past either one without pushing the button.

Christ · 11-05-2009, 09:34 PM

You have a floor shifter in the Tempo, right? You should be able to push up from D to N without being able to get into R at all, as long as you don't push the button.

My Candaian Topaz Sport was an auto 2.3 HSC until I blew the torque converter, then I swpaped it out for a 1.9 manual from an Escort Pony.

MetroMPG · 11-05-2009, 11:30 PM

Quote:

Originally Posted by Hermie

I was curious- Is it mechanically safe to pulse and glide in a non-hybrid, automatic transmission car?

Depends if you're talking about killing the engine in the glide or not. Most automatic transmissions aren't designed to coast in N without the engine running (lubrication issues).

Christ · 11-05-2009, 11:44 PM

Quote:

Originally Posted by MetroMPG

Depends if you're talking about killing the engine in the glide or not. Most automatic transmissions aren't designed to coast in N without the engine running (lubrication issues).

Darin -

This is one point that I would have agreed on several months ago, but now, I find that it's more than likely a misconception. I've been EOC'ing my Caravan for a little while now, literally for miles at a time, and have seen no problems in the transmission. I'll know for sure once I take Cara off the road, because I'll drain the fluid and drop the pan to check for problems in the trans before selling it, but I don't foresee any issues.

The thing about this, is that the lubricant in the bearings will remain there for awhile... it's not just going to let them dry out instantly if you shut the engine off. Because of this, I can't imagine another reason why you couldn't put the transmission in neutral and coast for a few hundred feet up to a stop sign or red light, or the like.

The relatively short distances that you can coast while in P&G or the like are almost guaranteed to be far under the manufacturer's recommended tow distance (read owner's manual) and speed, but almost all vehicles can be towed for a short distance at low speeds before damage is really even a consideration.

I'm not openly saying that it won't hurt anything, but in my (limited) experience, it's safe.