Idle
 

The new Scangage is awesome! One thing that is immediately noticeable is the difference between idle fuel rate when the truck is in gear or in neutral and cold or warm.

When cold, the engine idles at 1.2 gph in gear. It drops to 0.9 in neutral.

When warm (the 6.0 liter diesel/cast iron engine takes FOREVER to warm up) it uses 0.6 gph in gear and 0.4 gph in neutral.

Now I regularly put the truck in neutral at stop lights. This should have a significant impact, since my commute is stop-and-go.

And I'm thinking of an engine block heater.

And my next truck will have a manual tranny.

nice job, at least truckers
 

nice job, at least truckers can conserve too! Sometimes I like following big old trucks because they always try to time the red light to green, so they go slow for a reason.

If I had a CVT then I'll trail behind them more often, but with a man tran I'm usually in 2nd or 3rd when following them and that's a big FE killer ;(

With a manual tranny you can shut off the engine at will (when you don't need it) and turn it on half a second earlier when you need it via clutch.

Enjoy your new toy, I'll be getting mine soon enough!

I wonder why you're using
 

I wonder why you're using less gas in neutral with the auto. At least for my auto when it's cold it'll be at 2k rpms in neutral and then only like 1k in gear. Hmm.

Re: I wonder why you're using
 

I think it's because of the load that's placed on the engine. If there's enough of a load to drop the rpm's from 2K down to 1K that's fairly significant.

Hmm, I wonder, I've never
 

Hmm, I wonder, I've never really put all that much thought into it.

since initially doing the
 

since initially doing the idle warm-up experiment, i kicked myself for not recording the fuel consumption data in the few first minutes.

sludgy's post today about his idle gallon-per-hour observations inspired & reminded me to complete the test.

(full details in the original warm-up experiment thread).

the finished chart:

<img src="https://metrompg.com/offsite/warm-up-chart-complete.gif">

wait let me get this
 

wait let me get this straight...
If I'm driving and I come up to my light and put it in neutral instead of keeping it in Drive I'll actually gain mpg??????

Ya, the torque converter is
 

Ya, the torque converter (basically 2 fans suspended in trans fluid, one connected to the engine, the other to the trans) is what allows you to stay in gear even with the engine idling. But it takes more power to do so. So I can totally see why you would increase mileage by puting it in 'N' when at a light.

This is really an awesome
 

This is really an awesome thread. It is showing very simple things to do to increase fuel economy. These are things I would have never thought of as I havn't owned an automatic car in a while.

I wish there was a cheaper obd2 data tool out there. I think everyone that can afford it should have a scangauge. Just watching your MPG rise by doing simple things like putting your car in N must be amazing.

Thanks, I was about to give
 

Thanks, I was about to give up on my car. I actually went 4000rpm today because I was tired of not finding some way to control my fuel injection.

And thanks to Matt too. If it wasn't for this website I'd still be at 24mpg mixed driving. Now I'm at 28.

I imagine I will have to
 

I imagine I will have to start doing this, :p

Also, do you think we auto people coudl benefit from loosening up our throttle cables so that the car doesn't feel the need to always propel itself forward while in drive so much?

Re: I imagine I will have to
 

I thought that the "crawl" was a function of idle speed and torque converter stall speed. I think the solution would be to lower the idle, which would create less load on the engine due to the torque converter. Still better would be to shift into neutral. Best of all is to kill the engine all together.

I didn't know if the crawl
 

I didn't know if the crawl was the cable or what, thanks for the enlightenment, I know much less than I should about automatic transmissions.

Re: I didn't know if the crawl
 

I'm still pretty convinced that auto transmissions are witchcraft.

Quote:Best of all is to kill
 

At every red light ;O?

Re: Quote:Best of all is to kill
 

At every long one.

Quote:At every long
 

What's your minimum 30 seconds of ICE OFF time? That should be the savings equivilant of an extra mile you can go as opposed if that 30 seconds was ON and actually GOING somewhere instead of WAITING for a light to turn GREEN.

Seems to help, and so does
 

Seems to help, and so does the new intake hose. I got 27.6mpg 70-80% on the streets. This switching to N thing mainly works on big intersections since that's where the most idling is. When I put it N the rpms go up by 200-250rpm and go down to the same rpm as it was If I was idling in D. I'm now going to do this. Hopefully I'll break 28mpg 70% city driving next time.

Questions for Compaq888
 

With my diesel, the RPMs stay the same regardless of whether it's in gear or neutral. The engine definitiely uses less fuel in neutral and it stays at the same RPM as in gear. There must be some feedback control to keep idle RPMs constant.

Your idle RPMs go up when you put the car in neutral? Do all gas engines do this? Wouldn't the higher RPMs use more gas?

Do you have a Scangage to tell what happens?

no, it goes up for a second
 

no, it goes up for a second then comes down to the same rpm as it was in D. Here is how i think it works...I think Bunger will agree with me.

I stop, put in N. Rpms go up because there is less load for the same fuel input then computer realizes there is no load and lowers rpm in neutral to the same rpm as it was in Drive. When I put the car back in Drive the rpms dip to 500rpm because of the Torque converter and the engine adds more fuel to keep it at 650rpm. Both N and D are 650rpm. But the difference is N has no load so the engine uses less fuel to idle. In D the engine idles in same rpm but uses more fuel because the Torque converter is now working.

I don't have a Scangauge, I use mpg trips to see the changes in my gas mileage and this website to see what works and what doesn't work. I think so far my street mpg is 23-24mpg. While my freeway should be around 35mpg. Every month I do something new to the car which improves my mpg.

Re: no, it goes up for a second
 

Actually, I figured it out randomly one day waiting in the car when it was running. If I moved the shift lever ever so slightly between N and D, the engine would tach-up anticipating the need for more RPMs to sustain the need of the transmission's resistance. If I put it back into N, then it would tach back down to idle.

I've learned a few things from this thread, I think. For idle, it would take less fuel. But for coasting: I have always read that putting an automatic in N to coast doesn't save mileage because of a loss of vaccum or some sort, and that essentially you're not using any fuel at closed throttle until you reach a certain RPM. Wouldn't it take more fuel to keep an engine idling instead of coasting? Also, what part of the transmission will wear out becuase of placing the vehicle in N, then clunking it into D while stopped? ...mine sometimes is a pretty hard engagement in the Integra, even warmed up.

I'll give it a try and see what happens, but from a cold start, I leave the transmission in gear to heat it up quicker (is this correct?) I used to flip up to N to let it idle higher to warm up the engine faster (like waiting at a light on a very cold day, or at the airport parking lot ticket payment booth line).

I agree with Matt -- automatics are some kind of witchcraft -- I've said it before, but I have no clue what the heck goes on in there.

RH77

Oops, sorry.
 

Darn double post -- when will they perfect WIFI??? (Dammit)

Anyways, I forgot to mention that D-to-N basically is the engine's unexpected reduced load, then it figures it out and back to idle we go -- manuals won't tend to do it because of the lack of a TC. I miss my manual...

RH77

Quote:I stop, put in N. Rpms
 

I think this sounds right. I've seen some cars that the idle control is so smooth that you hardly notice a change in rpm's when shifting in and out of gear. It seems like my Durango was that way; I think.

Re: no, it goes up for a second
 

Yeah when the car is cold there is no point in flipping back and forth through N-D. Also the parts are stiffer when they are cold. When the engine is up to temp it's the best time to do it. Doing this will wear out the Transmission cable and the motor mounts. It should give a boost of 1 solid mpg if you do it the entire tank.