Overdrive button - when to turn off and on

[Thymeclock]

Originally Posted by Quiplet

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.

[metromizer]

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 :-)

[skyking]

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.

[TXwaterdog]

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.

[Quiplet]

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

[TXwaterdog]

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.

[TXwaterdog]

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).

[duffremle]

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.

[user removed]

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

regards
Mech

[user removed]

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