Overdrive= better fuel economy?

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NH07r51
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Overdrive= better fuel economy?

Postby NH07r51 » Sat Mar 22, 2014 8:26 pm

I live in NH and they recently changed the speed limit on the highway to 70. I realized i got better MPG at 85mph 2400-2700rpm than 75mph (2000-2200) from about 16-17 mpg to up near 20mpg. I just started testing but haven't done much driving. My question is. Does turning off overdrive stop your car from shifting as much therefore getting better gas mileage at speeds from say 45-60? Anyone else have any experience like this?


NH07r51
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Postby NH07r51 » Sun Mar 23, 2014 6:45 am

Has anyone else thought of this. It makes sense if it keeps the RPMs steady.

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akley88
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Postby akley88 » Sun Mar 23, 2014 9:46 am

All turning off overdrive does is keep you out of fifth. Do to my tires I get better mileage with overdrive on.

DanJetta
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Postby DanJetta » Sun Mar 23, 2014 1:25 pm

In theory, overdrive usually improves your gas mileage. The principle is that the gearing allows the engine to turn the wheels with the least amount of effort possible. This doesn't always directly correlate to RPMs but, more so, a combination of things, including the position of the throttle.

When you're on the highway, the drivetrain's job is to maintain your vehicle's speed, which is usually an easier task than bringing your vehicle up to speed. That's why turning overdrive off around town sometimes improves your gas mileage (though usually not a lot).

When you're driving 85 MPH, you're fighting more wind resistance than driving at 70 MPH, which is the equivalent of driving uphill – which means more effort required by your engine which means a wider throttle position (more gas). Even if it did save gas, at 85 MPH in 4th gear, I would imagine your engine would be screaming down the highway and searching for a gun so it could shoot itself. Not to mention the amount of heat building up in your transmission.

skinny2
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Re: Overdrive= better fuel economy?

Postby skinny2 » Sun Mar 23, 2014 3:15 pm

NH07r51 wrote:I just started testing but haven't done much driving.
I think you need to keep driving and testing. Something is not right about what you've tested so far. The faster you go the more fuel you use...dropping out of OD will burn even more fuel. The more you're in the higher gear the less fuel you use. The only time a lower gear can be better is when climbing hills. If you downshift and use less throttle this can result in slightly better fuel burn than lugging up a hill. No way it can result in a 3-4mpg difference.

My experience is the exact opposite. OH raised the limit to 70 a year or so ago. I used to run 75-80 and now run 80-85 and have lost about 1mpg on long trips. Best economy is around 45mph in OD. My typical commute is 50 miles of 55mph road, with lost of hills. I usually run 65-70 and average about 18mpg. I once tested my mileage by running 55mph for a week (and almost lost my mind....) but averaged 21mpg for that week.

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doctahjones
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Re: Overdrive= better fuel economy?

Postby doctahjones » Mon Mar 24, 2014 9:36 pm

skinny2 wrote:
My experience is the exact opposite. OH raised the limit to 70 a year or so ago. I used to run 75-80 and now run 80-85 and have lost about 1mpg on long trips. Best economy is around 45mph in OD. My typical commute is 50 miles of 55mph road, with lost of hills. I usually run 65-70 and average about 18mpg. I once tested my mileage by running 55mph for a week (and almost lost my mind....) but averaged 21mpg for that week.
i have the same type of results. best mpgs seem to be around 55-60 but i'm not old enough to drive that slow consistently. 70 isn't too bad but the 80 i like to cruise at sucks down the gas....

NH07r51
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Postby NH07r51 » Tue Mar 25, 2014 6:11 am

Ok so a little update, Ive been drying with overdrive off, and i must say. around my hilly town roads at around 45mph.. my mpg's have gone up. I believe this is solely due to the fact that the transmission does not go into 5th beer when i hit 50 on the straightaways or downhills, then have to shift back into 4th, or get "bogged" down in 5th. I know it sounds crazy, and maybe this is just me. but on the roads i drive often, kicking off overdrive works.. If anyone else on here drives on roads about 45mph that have lots of hills, let me know if kicking off your over drive leads to better or worse fuel economy.

who knows, maybe its just me 8)

skinny2
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Postby skinny2 » Tue Mar 25, 2014 6:46 am

I could believe it at 45mph on hills. Especially if you use a light throttle. Technically, your best mileage would be shifting to 5th on the straight aways or downhills but then downshifting right as you start up the next hill. You use almost zero gas when coasting and 5th will allow you to roll along further before you need to get back on the throttle.

Just watch that 5th beer. :lol:

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iheartmypathy
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Postby iheartmypathy » Wed May 14, 2014 7:53 pm

DanJetta wrote:Even if it did save gas, at 85 MPH in 4th gear, I would imagine your engine would be screaming down the highway and searching for a gun so it could shoot itself.
This literally made me LOL :)


hahaha... im still laughing :lol:

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eieio
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Postby eieio » Thu May 15, 2014 9:37 am

iheartmypathy wrote:
DanJetta wrote:Even if it did save gas, at 85 MPH in 4th gear, I would imagine your engine would be screaming down the highway and searching for a gun so it could shoot itself.
This literally made me LOL :)


hahaha... im still laughing :lol:
cracked me up too :lol:


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