O/D on or off when driving down the highway

[RVER]

I have always wondered when to use O/D and not to use it. I have a car, truck and MH. Today I found I drove on the highway for about 60 or so minutes with the O/D OFF. I wonder when it is appropriate to use it ON and when OFF. I do not pull a car yet.
How about on my truck, when to put O/D on and off?
Thanks in advance.

[Old-Biscuit]

RVER wrote:
I have a adjunct to this question. I also have a fifthwheel and pull it with a Chevy 2500HD diesel with Alison transmission. I can not get it to say it is in tow haul or O/D off with using the button on the shift handle IF it is in D but if in 3 Both of them work. I am not sure they are not working in D but that it does not light up indicating that it is that mode of tow haul or O/D off which is the same button. IS THAT WEIRD or what? I have put it in tow haul while in 3 and then shifted to D and I think it works the tow haul. I like tow haul mostly for the way it uses the tranny for engine braking when pulling the fifthwheel.

Per the OWNERS MANUAL for 2003 Chevy 2500HD

Automatic transmission equipped vehicles are provided with a button at the end of the shift lever which when pressed enables tow/haul. When the button is pressed, a light on the instrument panel will illuminate to indicate that tow/haul has been selected. Tow/haul may be turned off by pressing the button again, at which time the indicator light on the instrument panel will turn off. The vehicle will automatically turn off tow/haul every time it is started.


If you have an automatic transmission, you can tow in DRIVE (D). You may want to shift the transmission to THIRD (3) or, if necessary, a lower gear selection if the transmission shifts too often (e.g., under heavy loads and/or hilly conditions).


So the little 'trailer icon' should come on when you select Tow/Haul
(1st push of button on end of shift lever)
O/D DISABLE if you push button again

Push it again and back to Drive O/D


Just give me the dang manual LINK

[Harvey51]

Oh, I thought it was for gearing down on hills. Rather than using the brakes for a long hill I turn overdrive off. If that doesn't slow me down sufficiently, I use the brake until I feel comfortable shifting down to the next lower gear to hold an appropriate speed going downhill.

I don't like to use the brakes on a long hill because they get hot and could catch on fire.

[drsteve]

Consult your owner's manual.

[RVER]

I have a adjunct to this question. I also have a fifthwheel and pull it with a Chevy 2500HD diesel with Alison transmission. I can not get it to say it is in tow haul or O/D off with using the button on the shift handle IF it is in D but if in 3 Both of them work. I am not sure they are not working in D but that it does not light up indicating that it is that mode of tow haul or O/D off which is the same button. IS THAT WEIRD or what? I have put it in tow haul while in 3 and then shifted to D and I think it works the tow haul. I like tow haul mostly for the way it uses the tranny for engine braking when pulling the fifthwheel.

[Dave_H_M]

my car and truck I tow with does not have that OD thingie/selection on the shifter anymore.

matter of fact i think the top two gears in my F 250 are overdriven.

life is so much simpler now. :W

[mkirsch]

MEXICOWANDERER wrote:
If I may ask a question...

What does the designer and builder of the transmission say?

There is no discussion about this in the owner's manual?

You know real men don't read the instructions.

[Sam_Spade]

RVER wrote:
Thanks, did I do damage to drive with it off?

No of course not.

If you watch your tach, you will notice that OD increases the gearing just slightly and your engine runs 200-300 RPM faster without it.

OD is intended to help with gas mileage, mostly. YOu could run with it OFF all the time if you choose. In some unusual circumstances your gas mileage can actually be better with it off all the time.

[gbopp]

Older cars, trucks and RV's didn't have Overdrive. There are still many of them on the road every day.

[MEXICOWANDERER]

If I may ask a question...

What does the designer and builder of the transmission say?

There is no discussion about this in the owner's manual?

[time2roll]

D and go unless it starts hunting. My OD is 98% off when towing. First downshift and off it goes.

[Old-Biscuit]

I can't remember when or IF I have ever turned it OFF

I get in truck, start it place it in 'D' and go

If hooked up to 5th wheel I place it in 'D' and turn Tow/Haul ON

I turn Tow/Haul on sometimes when not towing


But turning O/D off......never.

[rsg63]

I leave mine on but of course in TH mode(Aisin 6 speed) unless climbing a decent sized grade or descending a grade. No temp increases at all, at any speed (even 80 MPH in Utah!) 🙂
Basically, it it hunts in and out of 5th and 6th, I turn it off, otherwise always on.

[j-d]

JIMNLIN wrote:
When my trannies TC clutch runs a lot unlocked or the tranny shifts up and down a lot I take it out of OD. Works with the car or my trucks.

This and other similar advice. If the transmission doesn't keep kicking out of OD and dropping back in, frequently, leave OD on. That's what we do with our E450. It has a four-speed called 4R100.

Newer Fords have a five- or six-speed with TOW/HAUL like the GM Allisons do. With those, just drive it in TH.

That's 'cause the TH transmission still uses Overdrive when it can. It just modifies its behavior under the assumption it's carrying a heavy load. This is a good assumption where an RV is involved.

[DrewE]

RVER wrote:
Thanks, did I do damage to drive with it off? I will leave on now that I know. NEW rig to me so getting used to it and did not know it had the on and off switch for O/D. LOTS to learn.

As others have said, you did no harm at all. I don't think there's any vehicle around that would overspeed the engine in drive (rather than overdrive) at reasonable highway speeds; locking it out is benign from the point of view of breaking things. If the transmission is hunting between overdrive and drive, it is better for its longevity to shift out of overdrive rather than have it keep changing gears, besides making for nicer driving.

Even things that at one time could damage the transmission or overrev the engine (like downshifting to low gear at too high a speed) are basically much impossible with modern computer controlled transmissions. If you move the lever to downshift and you're going to fast to do so, it will not actually downshift as requested until you slow down sufficiently. Even things like shifting into park or reverse while moving, on many transmissions at least, won't cause trouble because it won't do them until you're practically stopped. I wouldn't suggest testing these things out intentionally, of course, but it's nice to know that you're pretty well protected from any ill-advised or unintentional moves.