Better MPG coasting in Neutral or in Gear ?

[HTSS_TR]

According to Ultra Gauge instant MPG (similar to Scan Gauge), my '00 E430 consumes less gas while coasting in neutral than in gear. Existing highway at speed around 60-65 MPH coasting to red light ahead, my Ultra gauge shows 120-130+ MPG in neutral and 70-80+ MPG in gear. Also, I can start coasting in neutral about 1/8-1/4 miles farther than in gear. I thought that with OBD II equipped engines the fuel is cut off while coasting in gear. Remember that this particular exist lane near my house is about a mile long, it was safe for coasting down from 60-70 MPH to about 30-35 MPH at the end of the lane.

Can someone with Ultra gauge or Scan gauge confirm what I experienced ?

 

[sciphi]

Definitely in neutral. I'd get about 160 MPG in N compared with 130 MPG in D.

However, the repairs to my Buick's 4T65 from coasting in neutral cost about $700 considering all the "fixes" I've done to it from all the revving up it did over coasting in N, or far more than the gas saved. It would rev up about 500-600 RPM's dropping into D from N.

My transmission also can't be dinghy-trailered, so it doesn't like being dropped into N from D at speed. Make sure yours can can be dinghy-trailered behind an RV, and you shouldn't have problems.

Our Honda can be dinghy-trailered, so it isn't affected like my Buick was.

 

[needsducktape]

I may be wrong but to me its simple - Look at your RPMs in neutral and then in gear- Of course your gas mileage is better.

But then again, its kind of obvious in a manual trans car.

The only thing to keep in mind is the you have NO engine braking- So if you're on a super steep hill and rolling down you could wind up FLYING as opposed to in gear where the engine/gear will control the speed more.

Personally I like the feeling of flying off the edge -and getting free miles per gallon doing it. (I also make sure my brakes are always in good shape)

 

[Eddie]

Not a safe thing to do for a few oz of fuel.

 

[rationull]

Many newer cars will cut fuel when in gear with the throttle closed above 1200-1500 RPMs or so. In those cases, in-gear is more fuel efficient as well as safer and more convenient.

 

[dparm]

Originally Posted By: Eddie
Not a safe thing to do for a few oz of fuel.



I was taught in driver's ed never to let the car roll in neutral. If you have to take evasive maneuvers the last thing you want to think about is getting it back into gear.

Also puts excess wear and tear on the clutch, syncros, etc. Saving $20 a year isn't worth the possibility of a $600+ clutch job.

 

[d00df00d]

Originally Posted By: rationull
Many newer cars will cut fuel when in gear with the throttle closed above 1200-1500 RPMs or so. In those cases, in-gear is more fuel efficient as well as safer and more convenient.

^^ This.

My car is from 1996 and it does this. The stock onboard computer lets me monitor fuel injected in liters per minute, and when I let off the gas with the car in-gear it reads "0.0"; If I drop into neutral and let it idle, it uses 0.9 - 1.3.

 

[HTSS_TR]

The RPM in N was about 650-700 as it was at readlight, and it was 1400-1500 or higher in D. But if the fuel was cut off then doesn't matter what RPM was, it should be much higher than 70-80 MPG, unless the fuel didn't completely cut off.

I tried coasting in N on the long flat surface exist lane near the house, not on steep hill or curvy road. Saving gas is one thing, get myself in danger of not controlling the car is another.

It is possible that my Ultra gauge didn't calculate the instant MPG correctly, or it reads the information from on-board computer via OBD II incorrectly.

 

[fdcg27]

I have the same result with my low-cal version of the BMW e36.
The "mpg" gauge (yes, it actually has one) indicates lower consumption coasting in gear above idle than it does coasting at idle in neutral.
In both of the Hondas, you can actually perceive the return of fuel being injected as low engine speeds are reached coasting or braking while in gear.
For this reason, I usually coast down to a stop until around 1.2K revs, and then select neutral.
No harm done with a stick, and even if you were inclined to coast long distances in neutral, gear selection is so much second nature if you normally drive a stick that it isn't a safety concern.

 

[demarpaint]

Does coasting in Neutral in an automatic cause excessive heat in the transmission? I could swear I read that somewhere.

 

[ls1mike]

http://www.remcotowing.com/node/6
If you want to tow in neutral.

Leave it in Drive, you are not going to save enough cash to warrant the extra maintenance.

 

[ramechanic4]

Originally Posted By: demarpaint
Does coasting in Neutral in an automatic cause excessive heat in the transmission? I could swear I read that somewhere.


Probably vehicle dependant, I'm no transmission expert, I just take them out and put them in, I don't work on them, but I know some of them don't pump fluid through the cooler when in neutral. This would result in all the parts still generating heat from friction while coasting in neutral but no fluid running to the cooler. aka - higher temps.

 

[Hermann]

The Ultragauge in the Tacoma with a manual transmission, will read higher MPG's coasting in gear, if the grade is steep enough. If on level ground and just coasting up to a red light, the readings are very similar. When coasting up to a red light in gear, the fuel is reactivated at 1100 RPM, you can feel it as a slight surge, and the instant MPG reading will drop in half.

 

[JHZR2]

Coasting in neutral to a stop is ok. In an AT, ONLY do so if you know you will definitely stop. Otherwise you can damage your trans.

Doing it from speed to a dead stop only is perfectly fine, and we have multiple >200k ATs that have never been rebuilt.

In an MT you have a lot more flexibility. How I do it is as follows:

-if I know I'll need to slow but not stop, like due to a far off light, I'll coast immediately.

-if I know Ill have to stop, I will coast in gear to allow the injectors to shut off. I do this to about 1500 rpm, then coast in neutral.

- as opten as possible I try to get off the throttle when it makes sense.

-at all times drive like there is an egg between your foot and the pedal.

 

[tom slick]

according to the Scanguage, both of my vehicles will go to zero fuel flow when in gear (AT) at zero throttle while coasting. If I shift into neutral on the same hill fuel flow goes up to engine idling levels.

 

[Kiwi_ME]

Originally Posted By: demarpaint
Does coasting in Neutral in an automatic cause excessive heat in the transmission? I could swear I read that somewhere.


I seriously doubt that is true in any conventional auto. How would you activate the hydraulics to put it into gear if there was no oil pressure on start-up? But, turning off the engine while coasting is another matter, and no doubt where that perception came from.
----
Given that the engine will shut off the fuel when motoring (over-running) at over perhaps 1200 rpm at zero throttle, it's simply a matter of differentiating between "motoring" losses and fuel use at idle. Personally I wouldn't bother for the minimal difference, aside from the fact that under most jurisdictions it's usually technically illegal.

 

[Colt45ws]

I get more coasting in gear than in neutral.

 

[Steve S]

Originally Posted By: demarpaint
Does coasting in Neutral in an automatic cause excessive heat in the transmission? I could swear I read that somewhere.
No Though shifting to N adds to the clutch wear somewhat.

 

[kemo]

Originally Posted By: Steve S
Originally Posted By: demarpaint
Does coasting in Neutral in an automatic cause excessive heat in the transmission? I could swear I read that somewhere.
No Though shifting to N adds to the clutch wear somewhat.


you are referring to the clutch plates in the clutch packs right?

 

[eljefino]

My stick shifts show 0.0 milliseconds of injector pulse width coasting in gear vs "some" in neutral. And I can feel it kick back in. My 95 saturn and my dads 93 escort did this so it's not an OBDII thing specifically.