Downshifting for engine braking in an automatic

Grayham

Grayham

New member
My '99 4Runner SR5 is the first automatic I've ever owned. I've got a ScanGuage hooked up to it through the OBDII port.

I noticed that it didn't display '9999 MPG' (meaning that there's no fuel flowing into the engine) when I let off the gas and coasted like my previous manual transmission car did. Instead, it shows around 100 MPG. I can also verify this if I switch the display over to gallons/hour.

I figured out that I had to downshift it myself and keep the revs up for the fuel flow to stop. I do this because it actually makes a pretty good difference in my fuel economy.

I just wanted to make sure that there's not an issue with frequent downshifting.

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This is interesting. I just made a trip to UVA and back from my house and made it on a single tank with fuel to spare. Left with 3/4 tank and 70 miles on the tripmeter and the trip is a good 115 miles each way. Returned with a little less than a 1/4 tank and 305 miles on the trip meter. I used O/D off and downshifting into 2 and occasionally L around Charlottesville, and even with the A/C on I got amazing mileage. Is it worth the extra wear and tear on the gears though?
 
KellyJ said:
This is interesting. I just made a trip to UVA and back from my house and made it on a single tank with fuel to spare. Left with 3/4 tank and 70 miles on the tripmeter and the trip is a good 115 miles each way. Returned with a little less than a 1/4 tank and 305 miles on the trip meter. I used O/D off and downshifting into 2 and occasionally L around Charlottesville, and even with the A/C on I got amazing mileage. Is it worth the extra wear and tear on the gears though?
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This is what I'm trying to figure out.

With a manual, it's easy to rev-match when down-shifting, putting less stress on the synchros. An automatic will just down-shift (when selected) and will let the wheels speed up the engine, putting more stress on the transmission and engine.
 
Downshifting is fine. If it was really bad the car would somehow prevent it from being done or there would be warnings in the owners manual.
 
Interesting, So are you guys saying if you drive around town in 2 or lo, you get much better millage with the rpms up there a little?
 
twitchee2 said:
Interesting, So are you guys saying if you drive around town in 2 or lo, you get much better millage with the rpms up there a little?
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No, no. We're only discussing downshifting when you're coasting to a stop which keeps the wheels turning the engine instead of vice-a-versa. This saves a bit of fuel.
 
I travel up and down pretty intense mountain roads very frequently in Va and downshift to brake all the way down the mountain. Its alot better to use 2nd and Lo than burn out your brake pads.

I also enjoy shifting to brake instead of pushing the brake pedal.

Dont think it does any harm and saves gas sorta.
 
oh oh oh i misunderstood that, I defiantly use lower gears while going down hill up in the mountains. Not only does it apparently save fuel, but i feel like i have much more control
 
if your going to be doing that i would atleast recommend an extra tranny cooler, just to be on the safe side.
 
I think a general rule of thumb for engine braking is to consider the effects on all the components. For example if your brakes could catch fire or fluid boil causing you to lose all braking and die on a mountain, then I would say its ok to use a lower gear to keep you from having to use your brakes as much. On the other hand if the alternative is higher gas mileage I would consider the stress that you are putting on your transmission and just decide if its worth it to you. There shouldn't be any doubt as to whether or not the 4runner is meant to be driven like that under normal conditions but I guess if you want to say that "they put it there so they must have meant for me to use it" then I guess you've got something coming anyway.
 
I have a scangauge II and have been doing research on hypermyling.... Its just another word for working on getting really good gas milage. Ive noticed that with my 96 4runner, and most cars that are autos, you can shift from drive to neautral withought pushing in the button. But you must push it in to shift into any other gear.... Im guessing that they were designed like this because it is safe to shift from drive to neautral while driving. If you want some more info on hypermiling go to cleanmpg.com

Hope this helps.... :)
 
9074runner said:
I have a scangauge II and have been doing research on hypermyling.... Its just another word for working on getting really good gas milage. Ive noticed that with my 96 4runner, and most cars that are autos, you can shift from drive to neautral withought pushing in the button. But you must push it in to shift into any other gear.... Im guessing that they were designed like this because it is safe to shift from drive to neautral while driving. If you want some more info on hypermiling go to cleanmpg.com

Hope this helps.... :)
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But shifting into neutral is not engine braking. He's asking about going down to a lower gear.
 
just another thought on the subject. i think I read in the Runner manual that you can actually shift from drive to 1st. and the tranny will go down through the gears in a manner deemed safe by the computer (ECU). I believe this was implemented for off road and as a back up for brake failure.
 
I think most automatics have that. Even if you shift it into reverse while moving forward, it will not go into reverse until the car slows down enough.
 
nighthawk said:
I think most automatics have that. Even if you shift it into reverse while moving forward, it will not go into reverse until the car slows down enough.
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I'm not so sure that that statement is true in all cases.

Your best bet is just to assume that the transmission is not smarter than you are. ;):
 
Grayham said:
I'm not so sure that that statement is true in all cases.

Your best bet is just to assume that the transmission is not smarter than you are. ;):
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They did that in an episode of Mythbusters and they tried it on an older American car and nothing happened when they put it in reverse. Not say all cars do that, but I think most have this safety feature built in. Anyways, I only drive manual so not really something I really car too much about, but just thought I'd mention that someone did test that and that was the finding.
 
nighthawk said:
But shifting into neutral is not engine braking. He's asking about going down to a lower gear.
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Since the reason he was asking about downshifting was to save gas, he makes a good point that you can shift into neutral while driving. Obviously this should save more gas than downshifting.
 
rjyhdc4 said:
Since the reason he was asking about downshifting was to save gas, he makes a good point that you can shift into neutral while driving. Obviously this should save more gas than downshifting.
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Actually, this is not the case. Think of it this way:

If you're in park and idling, then of course you're burning fuel. I believe off hand, it's around .75
 
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