[ale] [OT] - Ethanol-free gas in the Atlanta area? - and gas saving tips

[Jay Lozier]

-----Original Message-----
From: Ron Frazier (ALE) <atllinuxenthinfo at techstarship.com>
Reply-to: Atlanta Linux Enthusiasts <ale at ale.org>
To: Atlanta Linux Enthusiasts <ale at ale.org>
Subject: Re: [ale] [OT] - Ethanol-free gas in the Atlanta area? - and
gas saving tips
Date: Fri, 20 Sep 2013 14:43:31 -0400 

<snip>

Hi all,

I wanted to pass along a bit more information about saving fuel, and some tips as to what not to do.

One technique I'm experimenting with that has the promise of both saving some fuel and being safe (if done properly) is called DWB, which stands for driving without brakes.  You don't literally do that, but you try to manage the momentum of your car and, whenever possible and safe, never touch the brakes.  If you press the brakes, that's an indication that you've burnt too much fuel to build up momentum in the car and you have to turn that momentum back into heat with the brakes and waste it.

Of course, in the real world, there are many times that you cannot just coast for 1 mile to come to a stop.  Also, if you're decelerating without touching the brake, the people behind you may not realize this.

This also relates to getting the fuel injectors to cut off.  In my car, if I'm going down a pretty steep hill, above 45 MPH or so, I can achieve DFCO by taking my foot of the gas.  Sometimes, touching the brake briefly triggers DFCO, but it usually does that on its own.  In my wife's car, however, you'd probably have to be going 55 MPH or so to achieve that, and that is probably unsafe.

What I'm about to say is controversial, and there is a big debate with proponents on either side of the fence on the internet.

Note that I'm only talking about automatic transmissions here.  One alternative with a car with P N R D 3 2 1, etc. on the shifter or cars with the "sport" mode and +/- shift controls is to shift the car from D to 3 (assuming a 4 speed gearbox).  This will cause the engine to rev up, decelerate the car, and allow you to get into DFCO or maintain it longer, and save wear and tear on your brakes.  Some people will shift to 2 and even 1 as the car decelerates and not hardly touch the brakes.  The consensus on shifting to 1 seems to be never above 5-10 mph and some say not unless you're stopped, in which case, the automatic goes to 1 for you.

I will go ahead and point out that the manual for most cars SAYS to do this downshifting in mountain terrain to avoid burning out your brakes.  That's not what I'm talking about.  I'm talking about just average driving, on moderate hills, at traffic lights, turns, and stop signs.

So, the controversy is: should you do this downshifting in average driving or not and does it harm the transmission.  I spent hours yesterday reading blogs and forums which advocated each side of the fence, do it and no harm, or don't do it and it will harm.

The consensus, for whatever that's worth, seems to be biased toward the don't do this, it can harm your transmission, and brakes are much cheaper to fix than the transmission.

I decided to go and ask my mechanic, whom is very knowledgeable and whom I trust.  It turns out that he agrees with the consensus.  He said that if you do the procedure just right, at just the right rpm, and under just the right conditions, it is theoretically possible to be OK.  (Side note - if you fee the car lurch when you downshift, you didn't get it right.)  But, he said  that's almost impossible to do.  He said there is a really good chance you WILL harm the transmission routinely downshifting except under specific conditions, like mountains, that require it for safety.

His advice, under normal conditions, and for average driving, is just leave it in D and let the computer figure out when to switch gears.  So, I'm not going to be doing any manual shifting on my car's automatic unless I have a specific need to do so.  And, that doesn't include trying to save a few dollars on gas.  The other time I'll probably just shift into 3rd and leave it there is when I'm going on a road where there are hills every half mile or so, and the transmission would be shifting up on the downhill and then shifting down on the uphill and repeating over and over.  Leaving it in third will lessen the shift cycles it has to go through.  Other than that, and mountain driving, I'll leave it in D and just pay the price in gas and brake maintenance.

I've also seen things that say change the ATF fluid every 30K miles, etc.  I asked the mechanic about that.  This is a used car, and I don't know the service history.  He said, that if I knew the service history, and knew that it had new fluid periodically, to continue that pattern.  However, he said that if I didn't know that, just leave it be.  He said that putting new fluid in a transmission with 100K + miles on it that's not showing problems can do much more harm than good.  Don't ask me how or why.

So, that's what I'm going to do, drive it in D(rive), leave it be, and let it figure out when to shift the gears.  I'm still trying to only touch the brake a minimal amount when practical.  I think I can eke another MPG or so out of it.  I don't seek out hills to use DFCO, because, even if I can be using no fuel going down the hill, I'm only going to be getting 8 MPG or so going up the other side in 3rd gear.

Just thought I'd pass it along.

Sincerely,

Ron


Downshifting on manual transmissions is generally done on gear at time, 
from 5th to 4th and is done on steeper hills to protect the brakes. 
In a car downshifting more than one gear is very rare but for trucks sequential downshifting
is sometimes done (6 >5 the 5 > 4, etc.)

If you are downshifting on an automatic I would do it one gear at time (4 to 3)
More than one gear may cause the engine to redline for either a stick or automatic.




-- 
Jay Lozier
jslozier at gmail.com
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