downshifting
Joined: Mar 2007
Posts: 135
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RE: downshifting
...At that point point you can sometimes feel a little shudder as it starts...
Registered User
Joined: Jan 2007
Posts: 4,322
From: Brandon, MS
RE: downshifting
ORIGINAL: tkundert2
Trouble is that I have formed a habit from years of driving of popping the shifter into neutral and coasting so I have to keep remembering to leave in gear.
Trouble is that I have formed a habit from years of driving of popping the shifter into neutral and coasting so I have to keep remembering to leave in gear.
Been Around A Long Time Member
Joined: Nov 2006
Posts: 2,631
RE: downshifting
ORIGINAL: JimBlake
Maybe it's a question of semantics. You could say during coast-down that the engine is NOT running. Meaning it's not injecting gas, and there's no combustion.
The engine is being turned externally by the momentum of the car or the slope of the hill you're coasting down. I imagine that if you're in the mountains and you can find a 6-mile downhill, the enginewould actually cool down.
The trick here is that as the engine continues to slow down & goes below some particular speed (I guessed 1300), the ECU starts injecting fuel again. At that point point you can sometimes feel a little shudder as it starts. If the ECU was unable to do this instantly, the engine WOULD stall. Restarting smoothly is the reason it switches at 1300 instead of right at idle.
Maybe it's a question of semantics. You could say during coast-down that the engine is NOT running. Meaning it's not injecting gas, and there's no combustion.
The engine is being turned externally by the momentum of the car or the slope of the hill you're coasting down. I imagine that if you're in the mountains and you can find a 6-mile downhill, the enginewould actually cool down.
The trick here is that as the engine continues to slow down & goes below some particular speed (I guessed 1300), the ECU starts injecting fuel again. At that point point you can sometimes feel a little shudder as it starts. If the ECU was unable to do this instantly, the engine WOULD stall. Restarting smoothly is the reason it switches at 1300 instead of right at idle.
Senior Member
Joined: Feb 2006
Posts: 6,290
From: Montana
RE: downshifting
I just recently did a trip to spokane, over and back (240 miles one way) yesterday and was playing around with these options in my wife's Lexus, it has "instant" readout on fuel economy, when left in gear and coasting It jumps right up to 100 gal/mile (the highest it goes) as long as I'm going over about 35mph, below 35 it uses some fuel to maintain the engine, I also noticed that over a fairly small strech with just coasting the engine did in fact cool down by about 1/8 of the way from "normal" temp. So back to the coasting in town or leaving it in gear I'm kinda split now, because under 35mph it did in fact still give me great MPG (around 30-40) however it wasn't as good as when I was traveling faster, I never did shift to neutral at that speed to test it though.... I wish I would have...
Registered User
Joined: Jan 2007
Posts: 4,322
From: Brandon, MS
RE: downshifting
ORIGINAL: sir_nasty
I just recently did a trip to spokane, over and back (240 miles one way) yesterday and was playing around with these options in my wife's Lexus
I just recently did a trip to spokane, over and back (240 miles one way) yesterday and was playing around with these options in my wife's Lexus
LOL, JK, just picking! [sm=icon_stickpoke.gif]
Dang I just realized how big of a post ***** I'm being today! I need to get to work
!
Been Around A Long Time Member
Joined: Aug 2007
Posts: 6,213
From: Wayne, NJ
RE: downshifting
Someone please explain the fuel cut-off mode to me.
It had always been my understanding that only diesel engines can cut the fuel & that gas engines need a minimum amount of fuel to keep the cylinder cool enough and the engine from knocking.
Regarding downshifting, I do it for better control through engine braking ...... also, downshifting to 2nd going into a hard corner and punching it half way though is soooo much fun!!!! I love losing people in the corners!
It had always been my understanding that only diesel engines can cut the fuel & that gas engines need a minimum amount of fuel to keep the cylinder cool enough and the engine from knocking.
Regarding downshifting, I do it for better control through engine braking ...... also, downshifting to 2nd going into a hard corner and punching it half way though is soooo much fun!!!! I love losing people in the corners!
Been Around A Long Time Member
Joined: Aug 2007
Posts: 6,213
From: Wayne, NJ
RE: downshifting
Oh ...... MPG is not improved noticably no matter what you do when coasting ...... I tested this on a full tank and babied the car, shifting to N whenever coasting. There was no MPG gain.
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