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Old 10-30-2011, 08:42 PM   #1 (permalink)
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Overdrive button - when to turn off and on

Having driven manual trans for most of my life - I'm at a loss as to the purpose and correct use of the overdrive button in my 2011 Hyundai Accent. The supplied manual had little help.

After six months of driving with the recommended 'overdrive on' I was unhappy with mileage. The guys at the dealership had different opinions. One man even told me 'overdrive off' was for aggressive driving which did not appeal to me. I could not get an answer that satisfied me so I experimented. Driving in stop and go seemed great after I 'turned off' the 'overdrive' button. Then I headed up on the interstate and the car sounded and felt like I was traveling 50 in 3rd gear. I immediately turn the overdrive back on and it settled into it's normal hum.

So - decided to research fuel efficiency and here I am. Most answers other places suggest to always leave button 'on' yet another said while driving smooth hills to turn it off.

I just want the best mileage - and the least wear on car. Thanks

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Old 10-30-2011, 09:03 PM   #2 (permalink)
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I've been toying with mine as well and I seem to get better mpg in traffic (stop and go) with the overdrive off. My thought is that my 2012 Focus seems to be getting better mpgs under heavier load (higher rpms) while accelerating so OD gets flipped off on hill climbs, takeoffs, and traffic where quick responses are more suited (I attempt to use 80% acceleration if possible). I get much better highway mpgs with OD on at speed and actually see a MPG loss when I flip off OD above 55mph.

I haven't really documented my driving habits yet but I did notice that my overall tank saw an improvement from 34mpg to 37mpg. On the improved tank I also didn't use cruise control at all. So I'm not sure if it's the hill assist/ OD off or my feathery foot. I just filled my tank up and I'll document this tank for the OD use and the next one I won't use it. Hopefully I'm doing it right... my onboard computer seems to think I am. But time will tell.
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Old 10-30-2011, 09:19 PM   #3 (permalink)
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This should have been covered in drivers ed, but seeing as how they don't teach people how to drive any more I'm not surprised that it was not.
The over drive button controls if the torque converter gets to lock up, stop and go traffic can be rough if it's constantly locking and unlocking, same with rolling hills at 45 to 50mph but for a lot of normal driving you want it to lock up so you have a more direct drive in the transmission.
Using it can also help your transmission to last longer.
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Old 10-30-2011, 10:46 PM   #4 (permalink)
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Quote:
Originally Posted by Ryland View Post
This should have been covered in drivers ed, but seeing as how they don't teach people how to drive any more I'm not surprised that it was not.
The over drive button controls if the torque converter gets to lock up, stop and go traffic can be rough if it's constantly locking and unlocking, same with rolling hills at 45 to 50mph but for a lot of normal driving you want it to lock up so you have a more direct drive in the transmission.
Using it can also help your transmission to last longer.
I doubt that it will help your transmission last longer, but it will help your fuel mileage by leaving it in "on" position all the time. Leaving it always "on" won't harm anything. Having it in O/D "off" mode will increase your available accelerating power, but at the expense of slightly reduced fuel economy.

Of course, if you never drive at speeds of over 40 MPH it will never engage anyway, so it becomes a moot point.
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Old 10-31-2011, 11:47 AM   #5 (permalink)
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I look forward to your results, Simon.

Being that I am a half-way conspiracy nut, I prefer to question the so-called 'expert opinion.' My 1999 Saturn manual trans gets outstanding mileage as is- and I 'just feel and hear' the correct shift. Any older model auto I had driven had no button choice. From the little I drove my 2011 Hyundai with OD off, it felt a much smoother ride in stop go traffic. I will continue to test this. I suppose it will help if I try to average the mileage per tank driving conditions. Thanks.
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Old 10-31-2011, 12:30 PM   #6 (permalink)
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Quote:
Originally Posted by Ryland View Post
This should have been covered in drivers ed, but seeing as how they don't teach people how to drive any more I'm not surprised that it was not.
The over drive button controls if the torque converter gets to lock up, stop and go traffic can be rough if it's constantly locking and unlocking, same with rolling hills at 45 to 50mph but for a lot of normal driving you want it to lock up so you have a more direct drive in the transmission.
Using it can also help your transmission to last longer.
The Overdrive lock switch has nothing to do with the torque converter locking up, but would prevent access from the over drive gear ranges, which on a four speed automatic would mean that the car would not shift beyond third if it was engaged prior to the vehicle shifting up, it may also alter the programming to hold onto lower gears until higher revs than in overdrive. In a 5 speed automatic with a single overdrive gear it locks out 5th, if there are two overdrive gears (4th and 5th) it would then again act like the 4 speed and not shift into the higher gear ranges.

In hilly or mountainous terrain where the car would start to hunt for gears because your desired speed was too high for the lower gear, but too low for the next higher gear according to the computer which is trying to maintain power output and fuel economy will generally default towards trying to hold onto speed. The excess shifting builds up heat and wears out the fluid and could burn up the clutch packs and brake bands within the automatic. In normal driving it is recommended to always drive in overdrive.

In the case of the 2012 focus that was mentioned its really a manual transmission with electronic servos actuating the gear shifts between two sets of input shafts and clutches in order to take advantage of the greater mechanical efficiency of a manual, but the simplicity to the user of the automatic's point and drive abilities.

The torque converter lock up is dependent upon engine speed, wheel speed, engine load, which is why you might mistakenly believe that by blocking the car from overdrive would affect this, as once you were in the speed range to lock up the torque converter it would unlock prior to shifing to the next lower gear.
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Old 10-31-2011, 04:16 PM   #7 (permalink)
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Quote:
Originally Posted by Hubert Farnsworth View Post
The Overdrive lock switch has nothing to do with the torque converter locking up, but would prevent access from the over drive gear ranges, which on a four speed automatic would mean that the car would not shift beyond third if it was engaged prior to the vehicle shifting up, it may also alter the programming to hold onto lower gears until higher revs than in overdrive. In a 5 speed automatic with a single overdrive gear it locks out 5th, if there are two overdrive gears (4th and 5th) it would then again act like the 4 speed and not shift into the higher gear ranges.

In hilly or mountainous terrain where the car would start to hunt for gears because your desired speed was too high for the lower gear, but too low for the next higher gear according to the computer which is trying to maintain power output and fuel economy will generally default towards trying to hold onto speed. The excess shifting builds up heat and wears out the fluid and could burn up the clutch packs and brake bands within the automatic. In normal driving it is recommended to always drive in overdrive.
Yup, you've got it exactly. The overdrive button should only be used when you're climbing hills (usually heavily loaded), and the transmission keeps shifting up and down trying to maintain your speed. You can also use it on long downhills to keep the transmission shifted down and give you more engine braking.
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Old 10-31-2011, 10:41 PM   #8 (permalink)
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Quote:
Originally Posted by Hubert Farnsworth View Post
The Overdrive lock switch has nothing to do with the torque converter locking up, but would prevent access from the over drive gear ranges,
that is likely true for some cars, but the torque in my Kia, which is probably very similar to the Hyundai, only locks in 4th. If you lock out 4th, you would prevent torque lock up. I don't have a overdrive lock out, but I do have a manual shift mode, and the torque won't lock at all in manual mode. Anyway, I agree that driving with overdrive on is going to be best for FE.
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Old 11-01-2011, 07:29 AM   #9 (permalink)
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Quote:
Originally Posted by puddleglum View Post
that is likely true for some cars, but the torque in my Kia, which is probably very similar to the Hyundai, only locks in 4th. If you lock out 4th, you would prevent torque lock up. I don't have a overdrive lock out, but I do have a manual shift mode, and the torque won't lock at all in manual mode. Anyway, I agree that driving with overdrive on is going to be best for FE.
Again there may be exceptions, however at least on new/newer cars for fuel economy reasons the manufacturers are trying to get the torque converter to lock up as soon as possible for fuel efficiency, and generally will also lock or remain locked in lower gears as long as the road speed is sufficient to prevent stalling/stuttering from the driveline, because while a torque converter slipping allows for the engine to idle without the car moving, this loss of efficiency because the wheels are always connected to the engine while the vehicle is in gear is reduced once moving and as the torque converter locks up its efficiency approaches but does not meet that of a manual's dry friction clutch.

In the example first presented in this post the accent seemed to feel more responsive in stop and go traffic because it was holding onto the lower gears longer and shifting less, which is usually detrimental to fuel economy due to the higher fuel consumption at higher speeds, this however is tempered somewhat by the fact that if you were driving in stop and go traffic you don't necessarily want the car shifting through all the gears all the time due to heat build up and lugging the engine when suddenly decelerating once again.
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Old 11-01-2011, 04:55 PM   #10 (permalink)
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Thanks for all the interest. I guess my idea of just 'feeling' the correct OD on or off is not the best way to go. However, if I use the OD off status while pulling weight on hill, then what is the purpose of the D2 and D3? Sorry I'm so ignorant about all this, just call me the little old lady from Pasadena.

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