Something got me thinking about this the other day. I was wondering if you guys had any input on the matter. My truck: 04 with a 5.4L, 3.73LS, 6" lift, 35" tires, 12MPGs around town. My question is, beings it is so damn expensive to regear I probably wont be doing that, do ya'll think that I would gain any MPG's around town if I turned the overdrive off? Has anyone tried it or does it sound like a decent idea?

 

sounds pointless

give it a try though. try 100 miles with...fill it up

try 100 miles without...fill it up

and compare the MPG

 

Just a question, but I remember reading somewhere that having OD off for long periods of time can cause issues because pressure accumulates in the tranny somehow? I don't think there would be an issue, then I just barely remembered reading about that OD thing a while back in the towing forum Now I also have 35's and 3.73's and my truck always seems to gear hunt on the highway. If I hit any type of hill, my truck will go right down out of OD. I am not really sure what I can do about it other than maybe pull OD off before I go up a hill on the highway. Happens around town too because at 40mph I am right over 1k rmps Maybe I need some power adders. Should I just throw on an intake? Then what else will I need?

 

Anything under 55 mph I have OD turned off. It keeps the rpms up a bit and it's not always shifting in and out of overdrive in town. Responds and drives much better this way IMO. Only time I turn on OD is above speeds of 55 mph.

CRF250 - You might want to try looking at getting a Gryphon tuner or somethingi similar. With the stock edge programmer that I have I can go down the highway at 55-65 mph and up a decent sized incline and not have to downshift anymore. I'm sure the Gryphon would be even better than the canned tunes from edge. Don't mess with an intake unless you have custom tunes.

 

I was just looking at a CAI with an xcal and VMP tunes I think I will ask for the xcal for my bday and then buy the intake myself and install them all at once

 

let me know how it turns out with the 100 miles w/o and 100 miles with.. im always looking for better mpg

 

I did this little experiment you are thinking of. I started at full and by half tank, I realized I was getting much worse gas mileage by having the overdrive off all the time. All of my driving was city driving. I found that it was taking forever for the truck to shift into the gear which kept the RPM's at 2K or below. Feel free to do the experiment for yourself, but I think you will just be wasting gas.

 

Thats what I was looking for, Thank you.

 

OD off should = higher continuous rpm
that seems counter-intuitive to saving gas.

just my 2 cents - oaw

 

I dont see how higher rpms which uses more gas for a longer time could be good for gas mileage.. my 3.73s 5.4l stock wheels and 255/70/17 tires get me 16.2mpg city with OD on at all times.

 

The way I see it, with my 35" tires, with overdrive off, I'm only pushing around 2,100 rpms or so up to 40-45 mph. So that isn't 'high' rpms. So in town driving, I'm keeping the rpms in the correct range to get the best fuel economy. Plus, it keeps the tranny from going into OD which drops the rpms well under 2,000 so whenever I need acceleration, it has to downshift, then go. I would much rather have it in 3rd gear so if I need to accelerate, it is ready to go when I step on the pedal. Once I get to 55 mph and above the rpms are high enough that OD can do its job and stay locked in to keep the rpms where they need to be.

 

Do the experiment and see what happens. Maybe you will have exactly opposite results of what I had.

Think about this:

-You are at a stoplight and the overdrive is on.
-The light turns green.
-You press your accelerator and about halfway between the next light, your truck shifts into the appropriate gear (3rd for me) to get the tach at 2K or below are you are able to pretty much coast to the next light or keep light pressure to continue through multiple lights.

-At the next red light, you turn off your overdrive.
-The light turns green.
-You press your accelerator and about halfway between the next light, your truck is still in second and not automatically shifting to the next gear as quickly as it would have if the overdrive was on. That means your rpm's are going to be higher for longer.

What will save gas? You will have to do the experiment for yourself, as driving habits may play a part.

 

Why would my truck be stuck in second gear? It goes into 3rd gear just fine - keeping the rpms under 2000 rpms.

Maybe I am wrong - but I think it uses more gas when the rpms are really really low and you try to accelerate. With big tires - that is a lot of weight to try to get to turn. By keeping the rpms slightly higher with oversized tires, the engine doesn't have to work as hard or dump as much fuel into the cylinders to try to get that amount of mass to turn. Am I wrong on this assumption??

I have an edge programmer - and for me, my 'average' mpg is slightly better when I drive with OD turned off at town speeds or under 55 mph basically. I mean we are talking about a difference of .3 to .5 mpg at best. I think personal driving habits, truck modifications, etc. etc. play a bigger role in fuel economy.

Like I said originally, I hate when I'm in town cruising around and say a light just turns yellow. You can either slam on the brakes and come to a halt in a hurry or step on it and get through it. If my truck is in OD and I step on it, I'm waiting a good full second or so before it downshifts into 3rd and starts to accelerate. Versus if OD is off and I step on the gas pedal and I'm accelerating now, no waiting. In town, at those speeds, I would much prefer to accelerate on demand.

I tested my rpms on the way to work and I can hit 55 mph before my rpms are at 2,000. With overdrive on it's 65 mph before I hit 2,000 rpms. So at town speeds, my rpms are definitely not in the higher range. 3rd gear is plenty for speeds up to 50 mph.