gas milage, axle ratios, overdrive

[John A]

I stopped at Toyota, Plano,Tx today to order a rear side marker light and got in a conversation with the parts manager. We were talking about gas milage with the V-6, and driving in or out of overdrive. Someone on this forum said not to drive in overdrive as the constant up and down shifting made less gas milage, this guy said if you were driving with OD turned off, the tranny did not lock up and your gas milage would suffer, he also suggested changing the final drive gear ratio, he said I probably had a 4.10 now and going to a 4.58 or so would likely improve the gas milage. I have not checked yet to see what rear end ratio I have. Any one out there had any experience with rear end ratio change?????.......................John A

[Shoprat]

Howdy John A.

Driving in overdrive on the flat or small hills is fine. This WILL increase your gas mileage. However, in very hilly country, or in mountains, don't use overdrive. The constant shifting is harder on the trans. What you save in gas mileage, you pay later in tranny overhauls.

As far as the rear axle ratio goes, he's fulla it. That 4.10 axle ratio means the drive shaft makes 4.1 revolutions to 1 revolution of the rear wheels . A 4.58 ratio means that the driveshaft makes 4.58 revs to 1 rev of the rear axle. Therfore, the engine has to make more revs to drive the driveshaft more revs to move the vehicle at the same speed. This sucks more gas.

You will accelerate more quickly with the 4.58, but you will burn more gas. To really get more gas mileage, you would have to drop down to a 3.90 ratio or so to burn less gas.

Case in point, I once put a larger engine in my Dodge pick-up. The pick-up had a 4.10 rear end that was installed with the 6 cyl from the factory. The gas mileage with the V-8 and 4.10 rear end was 4 miles per gallon! I then installed a rear axle ratio of 2.90. The mileage jumped to 13 miles per gallon. I lost acceleration, but gained mileage. It was, to me, a good trade off.

[Tom W]

My v6 locks up in other gears (torque converter)also the dealer says 4.10 ratio I use the OD as much as possible level ground & not to much wind,otherwise its locked out A little lower rear ratio would be perfect.

Averaged out it gets about 13.75 not anyworse in the mountains its the wind and speed that makes it drop like pushing a billboard down the road.

[Tom W]

I just saw Shop Rats anwser what I,m saying a lower rear would allow more time in overdrive,A higher ratio it would never pull in OD

[WME]

If your rig requires a lot of almost full throttle in O/D, then going to a 4:56 or 4:88 would you to use less throttle to maintain the same speed because the engine is in its power band and operating more effecently. Most O/Ds are like 15-20% the Toyota O/D is 29% way to much for a MH. Its almost to much for an empty pickup on anything but flat ground, but it made for good EPA numbers

If you turning 3700 in 3 with out O/D and thats how you normally drive it. Then going to a 4:88 would let you use O/D more often with out lugging the engine. A 4:88 would let you turn around 3400 in O/D making the engine run with a higher manifold vacuume, getting better gas milage and better acceleration. So you can have your cake and eat it too if you make some correct chioces.

Big slow turning V-8's are a whole different animal.

WME

[turtle]

.... also suggested changing the final drive gear ratio, he said I probably had a 4.10 now and going to a 4.58 or so would likely improve the gas milage. I have not checked yet to see what rear end ratio I have. Any one out there had any experience with rear end ratio change?????.......................John A

I have 4.56:1 gears in the diesel. I did not notice a change in the mileage but it will pull tree stumps now :-)

Chances are you have 4.10:1 in your V-6 as that is what I have on my 1991 V-6 (until I change out to lower gears).