Overdrive question.....

[kentj]

Just wondering when you guys are towing do you take the tug in and out of overdrive depending if your going up hills vs driving the flat sections??

[Lisa M.]

Just wondering when you guys are towing do you take the tug in and out of overdrive depending if your going up hills vs driving the flat sections??

I'm glad you asked that question! I have an overdrive button thing on the end of my gearshift and haven't a clue when to use it. I should take out the manuel and find out!

[CD Smith]

The question should be, "How can I use my overdrive to optimize MPG?"

To accomplish this I have modified my Escalade's transmission control signals so I can select the optimum gear for all driving conditions. This includes the Torque Converter Clutch (overdrive), 4th gear, and 3rd gear.

1) Flat to minimum rolling hills - 4th gear and TCC engaged (this is a direct drive through the transmission with a gear ratio of 0.7) - 1670 RPM - 30% to 50% throttle position - 18 - 19 MPG.
2) Rolling hills to slight inclines 4th gear and TCC disengaged - 1900 RPM - 45% to 60% throttle position - 16 - 18 MPG.
3) Slight to moderate inclines - 3rd gear and TCC engaged - 2200 RPM - 50% to 75% throttle position - 12 - 16 MPG.
4) Moderate to severe inclines - 3rd gear TCC disengaged - 2800 RPM - 60% to 100% throttle position - 8 to 12 MPG.

1st and 2nd gear are used only to start from a standing stop. Generally I never let engine RPM exceed 2,000 RPM (except as stated above) even when starting from a standing stop (towing and not towing).

Obviously these are averages. An example would be 'Flat to rolling hills (read interstate overpasses)'. Engine speed would remain at 1670 and throttle position will increase to 100% momentarily. I usually do not allow throttle position to remain at 100% before I down shift by selecting a lower gear.

My advise is to know your vehicle including HP, torque, transmission, and differential ratios. Get a digital readout that shows RPM, MPG, etc. Then start experimenting. You'll be surprised at how much you can save on fuel costs. Remember the difference between 14 and 15 MPG for a 300 mile trip is approxinately 1 gallon of fuel. Thats $4.00!

[E. Graham]

When we first began towing, we were advised by our instructor to disengage overdrive:

- to reduce the use of the tow vehicle and trailer brakes when going down any steep or extended hill (going down steep hills, we also move into 2nd gear and find that often we don't need to touch the brakes at all)
- if we need a significant burst of power for passing
- when testing the trailer brakes before driving away

[CD Smith]

When we first began towing, we were advised by our instructor to disengage overdrive:

Doing this will not damage you TV.

The only problem with it is the torque converter is functioning and you are using fuel to heat the transmission fluid (due to the fluid coupling slip) and this heat is being transfered to the air passing over the transmission oil cooler. Not very efficient use of $4.00 fuel.

When the overdrive (TCC) is ON (for most automatic transmissions) a clutch in the transmission connects the drive shaft directly to the engine crankshaft thus eliminating the torque converter and applying more of the engine power to the drive wheels. Much more efficient.

The modifications I have made to my transmission controls allows me to select a mode that is not available on the standard configuration. That is having the TCC engaged when in 3rd gear. Again eleminating the loss due to torque converter slip.

[Darwin Maring]

Our Chevy Silverado has the button on the shift lever and it is used when towing. When I press the button a light lights up on the dash that tells me it is in tow mode. What it does is allow the vehicle to stay in the gears for a longer time B4 shifting and keeps it out of overdrive.

The book says to use it when the truck shifts up/down to many times (Hilly Conditions). I do not need to use it on flat open roads where it will not shift back and forth so that is when I use the Overdrive.

Click and Clack stated in one of their articles that using the engine on a regular basis to brake the vehicle would not be good for the transmission, rear end and engine as it puts additional wear on these items and that it is far less expensive to wear out the brakes than drive train parts.

This is why having brakes on the egg is a major plus.

Click and Clack can B heard on the radio on weekends and are in a syndicated column in the Washington Compost each Sunday.

I personally believe that having the ability to use the engine to help slow the vehicle is a Major Plus when the situation warrants. That is the only time I do that.

[kentj]

Wow thats a lot of info when all I ask is it ok to take your TV in and out of overdrive as your towing? LOL. But I think I got want I needed to know.

thanks

[Pete Dumbleton]

There are many different transmission designs and even some tow packages include different shift points, so the answer of how to use OD lies in the owners manual for YOUR particular vehicle. Comments on groups like this are very informative, but the maker of the transmission states what's best for your transmission in the manual. Read it several times.

[Alf S.]

Hi: We have a 2002 G.M.C. 4.3ltr. V6 with a tow/haul transmission. If you engage this button, located on the end of the shifter while towing at speed, the first thing that happens is the tranny comes out of O.D. For extra power, and to put less strain on the tranny, this is important... but fuel mileage will suffer. An extra large volume tranny cooler cost about a hundred bucks+ install may save thousands in tranny overhauls. I am not a "Techy" but I do try to use my equipment wisely. I just had some bumper stickers made that say "I AM DRIVING AS FAST AS I CAN AFFORD"
Alf S. North shore of Lake Erie