I have a 99 f-150 4X4 5.4 auto w/ 3.73
My brother and I had a descussion on when to and when not to put it in overdrive, for the best mi. he felt that anything above 45mph is best.
he has a explorer V-6. but said that it was good across the board.
I thought that was BS. Don't you have to Be at the right rpm to get the best mpg. and what would be the right rpm? If a engine is turning over to slow wouldn't that make a engine labor to much and reduce the mpg?
Around town 35-50 I have the OD. off Hwy. OD. on at 65MPH - RPM's around 2.5

 

That is correct about the RPM's. The trans is designed to always be in OD selection. I put it in OD when I get to about 55 or so on the freeway. I do not know what the most efficient RPM is, play around with it and see what RPM's it lugs at the most. Just above where it isn't luging to much should be about right.

 

Thanks Sidewalk for the info.

 

Depends a bit on the driving situation - is there hills, load in the truck, etc... My truck naturally drops into OD at speeds above 45 mph, if I'm not on the gas. Sits at 1300 rpms or so. Of course with my setup, I'm only turning 1500 rpms doing 55, and doing 1900 at 75. I just leave it OD unless the tranny starts hunting, the I know to drop out of OD.

 

Thanks Gopher !

 

Sounds like good advice. I just choose to stay out of auto while in town.

 

My Dad and I had the coversation about the same thing. If you're driving in town (say a bit over 40mph so it kicks into overdrive) and on relatively flat roads, your gas mileage would be better as long as your right foot isn't to heavy to keep your speed up and preventing a downshift, you're better off with leaving you're overdrive on. The reason my Dad likes having it off is because it gives you better engine braking because of the higher RPM. I guess I'm just the young pup and i'll use my brakes to stop because that's what they are there for.

That's my two cents worth. I think it comes down to the conditions you drive in.

Have a good one,
01Silverbullet

 

I use OD all then time. Very rarely do I turn OD off. And usually when I do, it's just for the heck of it. If I'm in a situation like hilly conditions in the 40-50 range, it stays in 3rd anyway. Oh, and this goes for when towing too. I tow a boat that weighs over 7000#. It stays in 3rd a lot more only shifting into OD when the speed is there and I'm not climbing or otherwise under a load it can't pull in OD. I say let the truck do what it was build and programmed for.

 

Thanks all for the info. Craig

 

Based on the recommendations of FactoryTech and others who seem knowledgeable on the subject, I leave mine in O.D..