Any damage to auto transmission when coasting in Neutral - Fuel Economy, Hypermiling, EcoModding News and Forum

sl2eggplant · 06-10-2010, 10:21 AM

Question is for my 99 Saturn SL2 Automatic

I don't drive in an area that will allow me to pulse and glide. I can't even do any decent pulse and coast since the roads in metro Detroit are relatively flat and I drive during rush hour traffic.

My general question is ... can you harm an automatic transmission by frequently going from D --> N --> D, in an aggressive pulse and coast strategy.

Personally, I don't plan on doing this very often but there are a couple of instances where I can coast any where from a 1/8 to 1/4 mile.

Angmaar · 06-10-2010, 10:28 AM

If you can "flat tow" your vehicle it should be fine EOCing.

PaleMelanesian · 06-10-2010, 10:59 AM

I'm pretty sure that vehicle is on the "flat tow" list, allowing engine-off coasting. Double-check, but I think it's fine.

Engine-on coasting is fine for any automatic. The D-N-D shift is no problem whatsoever.

MARTINSR · 06-10-2010, 04:38 PM

I have to tell you, I was coasting in neutral with my SHO and found that first of all, it didn't save me enough to do it! I drove thru two tanks of gas, one hypermiling with coasting in neutral and the other with coasting in drive and found that there was such a little difference it wasn't worth it to me. The thought of breaking that POS trans that cost about $2000 made me stop doing it.

In my car that I am building it has a manual transmission and I will be coasting in neutral or with the clutch despressed. But with my SHO, I decided the gain wasn't worth the chance of damaging the tranny.

Brian

MARTINSR · 06-10-2010, 04:40 PM

By the way, I did find that you could coast in neutral WAY longer than I ever thought! It is easy to coast BLOCKS from only 25 or 30 MPH. It is wild how far you can coast. But that goes for in gear as well. There is a little pulling so you can even "coast" further.

Brian

sl2eggplant · 06-10-2010, 08:36 PM

Thanks all for the input. I did a little mini Neutral coasting on my drive home from rush hour ... and it was difficult to say the least, making sure that synchonized my moves so that I could push the gas pedal. I have never driven a stick shift so I'm not used to all the shifting around.

MARTINSR · 06-10-2010, 09:35 PM

By the way when I say a "gain" it was honestly within error, we are talking a couple of tenths of a mile per gallon different.

Brian

sl2eggplant · 06-10-2010, 10:23 PM

MARTINSR, I believe you. In an average commute through a metropolitan area, there are not many opportunities to coast driving to / from work with everyone else. I would guesstimate 1-2 miles of coasting for my 64 mile daily commute ... so instead of running at 2600 rpm in D, I would be running 1200 rpm in N. Its not much of a savings without ideal road conditions. Every little bit helps and will add up especially in combination with other hypermiling tactics, so I will just keep it as one of tactics when the road permits.

Thymeclock · 06-10-2010, 11:48 PM

Quote:

Originally Posted by MARTINSR

I have to tell you, I was coasting in neutral with my SHO and found that first of all, it didn't save me enough to do it! I drove thru two tanks of gas, one hypermiling with coasting in neutral and the other with coasting in drive and found that there was such a little difference it wasn't worth it to me. The thought of breaking that POS trans that cost about $2000 made me stop doing it.

In my car that I am building it has a manual transmission and I will be coasting in neutral or with the clutch despressed. But with my SHO, I decided the gain wasn't worth the chance of damaging the tranny.

Brian

We had this same discussion in another thread and it's good to see that I'm not the only one advising against it. The potentially damaging action comes not from coasting in neutral, but from when you shift it back into drive. I recently stopped by my local Aamco shop and asked this specific question. They told me the same: don't do it.

What you can do safely however is to coast in neutral to a stop, as when you are approaching a stop sign. On local streets in neighborhoods that have a stop sign at every corner this can increase FE. As long as the vehicle speed is zero (or at least under 10 mph) the A/T will go into first gear when you shift back into drive and it won't harm anything.

PaleMelanesian · 06-11-2010, 10:15 AM

You really need some kind of MPG gauge to know whether it's working or not.

The SL2 in the OP is flat-towable, like behind an RV. As such, it's designed to be run in N all day long.