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Old 06-10-2008, 03:52 AM   #1
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P&G/coasting.

I've been tring p&g for a 4 days now. and in the first two days i eached the highest mpg ever in this car 37.5mpg.(thats alot considering the car is automatic and a 3 speed automatic to boot)
But i'm extremely unconfortible with the idea of turnin the car off in med coasting. both mechanic and safety reasons.
But the other day i timed the differience between p&g well shifting into Neutral and just lifting off the gas. Its a huge differience. on level highway i coasted 12 seconds just lifting my foot off the gas. and 18 seconds shifting it from drive to neutral. Why does the car slow down so fast just lifting my foot off the gas?
And one more thing. my wife drives a 2007 Vibe(or Matrix) and when i tried the same two styles it was 13 seconds just lifting off the gas and close to 25 seconds shifting it to neutral. What in the world??? I know my tercel and the Vibe two completely different transmissions. but what is going on excately? and should someone even p&g on flat level road or in the city? I know go downhill is the best. But with a 3 speed auto, i need all the tricks in the book.(btw my goal is hit 40mpg...well 40+ would be GRRRRRREAT but i'm shooting just to reach 40mpg at less once)

I've notice some are worried about shifting to neutral cause of what damage could happen. But next time you drive, try both ways. that so called "kick" shifting it back to drive happen both ways because when you lift up the gas, the transmission goes out of gear. when you push the gas again you can feel it shifting back.
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Old 06-10-2008, 07:15 AM   #2
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It slows down so fast because of engine braking. Instead of the engine powering the wheels, the wheels turn the engine. When you lift off the gas, the transmission does NOT go out of gear, but in an automatic the RPM can drop because of the torque converter.

As for the difference between one car and the next, there's many factors:
- aerodynamic drag
- weight
- engine size
- gear ratios
- tire rolling resistance
- torque converter design
- locking torque converter behavior

Watch the tachometer when you do your next comparison of coasting in D vs. coasting in N. RPM definitely goes down in N.
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Old 06-10-2008, 02:59 PM   #3
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only the vibe has a tachnometer. the tercel doesn't. if the transmission doesn't go out of gear when lifting off the gas. why is it that everytime you reapply the gas (even extremely low how amount)you can feel the transmission shift back into gear? its the same feeling when shifting from N to Drive. or am i getting the wrong feelings? LOL
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Old 06-10-2008, 05:27 PM   #4
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To be clear please tell us if each of the vehicles is a manual shift or an automatic. That will help this discussion. The ScanGaugeII if purchased will tell you what RPM you are at on a 2 second delay from instant.
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Old 06-10-2008, 05:31 PM   #5
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You're misinterpreting your butt dyno. You may be feeling the torque converter locking. More likely, you're feeling it downshift. When you coast it probably coasts in 4th, but then when you step on the gas again it downshifts to 3rd.

I'm not the end-all be-all of transmission experts (not an expert at all), but I'm 99.9% sure that no automatic transmission goes into neutral when you let off the gas. Certainly none that I've ever driven does.
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Old 06-11-2008, 04:24 AM   #6
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i'm not sure either holycow. 1fixitman like i said the car has just a 3 speed auto.(yup 3 speed auto, not 4th with o/d. it sucks) and the 4 speed auto tercel's get 35mpg easly. So i'm tring to find all tricks i can. and i don't have the $$$ for a scangauge. My budget for the car at the moment and the next few months(besides paying for gas) is super cheap($30 max) Thats why i'm really wondering about the p&g/coasting.
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Old 06-11-2008, 06:23 AM   #7
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Hmm...I wonder if you could hack up a gear indicator that tells you exactly what gear you're in. There's nothing like live data to help you find the best way to drive your specific vehicle!
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Old 06-11-2008, 09:41 PM   #8
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Tranny

I'm not the end-all be-all of transmission experts (not an expert at all), but I'm 99.9% sure that no automatic transmission goes into neutral when you let off the gas. Certainly none that I've ever driven does.[/QUOTE]

Although our Kia is listed in the Garage, We also have a '93 Seville.
(it's the one that looks like an Sts but it's not)
This transmission has an electronic torque convertor that will slip in and out of gear on purpose... WHEN in O/D..increasing gas mileage by coasting .It is a four speed Overdive auto.

I learned about this when setting it up for towing to go to Yellowstone last summer.
As a result when towing our popup the tranny should be kept in 3rd which is Drive but the convertor is locked. This prevents slippage at freeway speed.

By the way nice ride from san diego to yellowstone and back. We averaged 22 while towing!!!!!!!! pretty good for that car with a storage carrier on top also.

Just some useless info.....LOl
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Old 06-12-2008, 06:48 AM   #9
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I don't disagree that torque converters allow slippage, but an unlocked, slipping torque converter is not the same as neutral. All torque converters unlock when you're off the gas pedal, AFAIK. Mine does, but if I put it in N then the tachometer drops and I coast longer.

Try it in your Seville.

I wish I had a '93 Seville. That's a nice ride.
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Old 06-13-2008, 04:43 AM   #10
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I put a new thread about this in the other forum.but i may have given worse mpg's p&g this time around.(read the thread in the general area for most details) I may have to go back to just lifting of the gas and now putting it in "N"
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