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. :confused: Thanks

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.

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.

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.

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.

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.

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.

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.

"OD off" prevents the car from going into the highest gear. If you are climbing a steep hill with OD ON, you will notice the vehicle will lose speed despite your stepping on the gas pedal harder. If you step on it hard enough the A/T will compensate by downshifting into a lower gear to provide more power at a higher engine RPM.

If you want to use that overdrive to augment your fuel mileage, you'll need to use it with a fuel mileage computer that gives instant feedback. I've driven for years in what I would describe as 'seat-of-the-pants maximum FE mode' with no computer. I bought a scan gauge and have since been educated :-)

I travel across steep mountain passes, and switch OD off on my camry to maximize engine braking and to prevent shift hunting or cycling on the uphill portions.
My dodge truck has sufficient torque to climb the grades in OD at 50 MPH or above. It also has an exhaust brake for the other side of the hills.

So, I haven't filled up yet but I've driven about 300 miles (using my onboard computer). I'm getting slightly better fuel economy by flipping off OD while at speed climbing hills. When accelling from a stop at 80% wot I'm not seeing and increase of FE but rather I'm seeing a reduction vs slow acceleration. However, I am seeing an increase in FE when coming to speed from a stop with OD off over having it engaged when acceding at 80% wot. I'm also seeing an increase in FE when 80% wot with OD off vs 30-70wot with OD on from a stop. A 20% WOT push with OD on gives me the best mpgs/FE but only slightly. It really is 0.1 mog difference and coming to speed is better for my safety and sanity when doing an 80WOT push from a stop with OD off.

So in conclusion, (I still have to run the numbers and another tank). It looks like OD being used under load while climbing steep hills at 80%wot saves gas. It does not seem to save gas/FE when coming to a slow steady acceleration speed. Slow and steady likes the Overdrive engaged. My car also likes OD off/ disengaged when under heavy load like an 80WOT push from a standstill.

Looks like I'll need to get that onboard computer - sounds like fun too. Maybe a Christmas present for myself. I think I'll print out these replys to help out. :) Amy

Haha, it's like playing a video game. And your high score is rated in mpgs. Btw, on this tank I'm not flipping the OD off and I'm registering around 35mpg vs the 38 I was getting. So I'm thinking there's Merritt to playing with the OD.

MPG Update,


I've driven almost 500 miles and tested the flipping OD off and I saw a loss of over 2mpg (from 38 to 36mpg) over Flipping it off on accelerations and steep hill climbs. Basically, OD off saves FE when under heavy load changes. (Flipping off OD when taking off from a stop at more than granny pace, OD off when climbing steep hills, OD off in traffic/ passing).

The main reason I'm thinking switching OD off is helping me is that it's preventing a downshift. When I stomp on it enough to get a downshift that's when I see FE really drop. When hill climbing even keeping a steady pace the engine will commonly downshift and with OD off the car won't downshift, instead it will hold a higher RPM.

OverDrive is best left on when driving around normally and on flat surfaces. I've seen an increase in FE for using Overdrive when setting pace at most speeds city and highway. It's when that pace changes in a sudden manor that FE gains can be had by switching OD off (heavy load).

What I've been wondering about is why they only used OD as a 4th gear? It seems to me they could instead use them as gear splitters and then the OD could function as 2nd, 4th and 6th, with corresponding increases to both performance and mileage.

Doesn't the Hyundai have the dual clutch 6 speed transmsion. Basically an automated manual?

regards
Mech

Pretty sure both the Focus and Hyundai are dual clutch 6 speeds. OD off would be a good strategy when you are climbing hills that have too steep a grade for your tallest gear (which is really for flat ground or very slight grades).

If you allow the engine to get below it's torque peak in too high a gear you are wasting fuel. Not sure which gears are overdrive but that can get confusing if the final drive is higher or lower ratio. Bottom line is acceleration should be brisk for best mileage, Around peak torque should get you very close. Slow acceleration means slightly higher mileage (than brisk) but for a considerably longer time. Try to maintain your 80% load on acceleration as long as ti does not keep you in lower gears. If the grade gets too steep then go to a lower gear. Avoid WOT fuel enrichment unless it is unavoidable, lower gear is the better choice.

If your car has the ability for manual gear selection then just manually pick a lower gear that allow 80% load and the speed desired. If that does not keep you going uphill at the desired speed then you will have to increase your load, or reduce your gear selection and possibly increase the load. Another option is to gradually let your speed decrease as you reach the peak of the hill-mountain then let the downhill portion get your speed back up to the desired average speed.

regards
Mech

I have the low end Accent. I would like to get the autotrans someday.

Interesting. I always thought slow acceleration was better for FE.

Most here recommend acceleration at 80% of wide open throttle. While it will use more fuel per instant of time, you get to your desired speed much faster than very gradual acceleration. Understand that WOT can be a confusing term. Does it mean you have it floored? Does it men you have no manifold vacuum?

I have found that the best rate of acceleration in any automatic is as fast as you can accelerate without delaying the up shifts in the transmission.

Try accelerating and make a note of the speed at which your transmission shifts into the next higher gear. Gradually increase the throttle position on each of the next accelerations until you get to the point where the transmission stays in the lower gear longer than at lower throttle positions.

Then back off until you have found the "sweet spot" where you are not delaying up shifts but accelerating at the perfect rate, just bellow the shift "hold" point.

That gets you to speed with the least amount of fuel consumed and allows your car to spend more time cruising instead of spending more time accelerating. In watching my cars that have instant fuel economy I saw that the difference in fuel consumption would be fairly small, while the time accelerating could be as much as 50% less. Getting there faster uses less fuel when you consider the time spent at a higher rate of consumption.

regards
Mech