(O)drive on or off?

[watson5]

We are going to be towing our 06 Fleetwood Pegasus 260XP from Montana to Florida this November. Do most of you tow with the Overdrive on or off?
Does it make a diffrence if you have a gas or diesel tox vehicle?
thanks...

[dthurk]

Overdrive off is safer for the transmission.  It really should depend on a lot of factors, weight of trailer, tow capacity of vehicle, terrain traveled, etc.  When transmission starts hunting, time to drop overdrive.  If you're close to the max tow rating on your vehicle, time to drop overdrive.  Don't have any experience with diesel.

[tlhdoc]

IF my tranny isn't shifting back and forth I tow in overdrive.  My tow capacity is 7300 pounds and I am only towing around 3000 pounds so I don't think I am pushing it.  When we get into hills/mountains then I lock out the overdrive.

[brainpause]

On the Sunnybrook board where I hang out, many of them drive in OD with their diesels. Diesel engines have a lot of torque at low engine speeds, so when their trans switches to OD for lower RPM, they still have the torque to turn the wheels.

We have a 5-speed, 5th gear being similar to OD. When climbing a long hill, I usually just cruise in 4th (or 3rd if less than 45mph). Really keeps the engine from struggling, and keeps the clutch from slipping. Out on the open interstate, I can usually cruise in 5th gear.

Larry

[GeneF]

My Silverado has a tow haul mode which is supposed to change the shift points on the transmission.

I generally tow with the tow haul mode on and in drive which would be overdrive.  

If I am in hilly terrain where the transmission is constanly shifting, I will drop to third which takes it out of the overdrive mode but most of the time it is tow haul on, and in drive.

Generally, the truck knows more about when it needs to shift than I do.

[pershingd]

I tow with the OD off in my Ram regardless of terrain. I've found that it handles terrain changes better and, get this, gets about 1-1 1/2 MPG more out of OD than in. I usually get between 14 - 15 mpg when towing the pup.

When I first got my pup, I noticed that the cruise control (yes I use it too) was having to open the throttle more to maintain speed in OD than with out the OD. More throttle means more air, more air means more fuel, more fuel means less mileage. I know that I'm oversimplifying this a lot and I'm sure people that will correct me on it.

Just my .02.

David

[CAPEd CODger]

I'm surprised that nobody said the old stand-by; "Consult your vehicle's owners manual".

The '97 Ford pick up manual says tow with overdrive off. I, however have towed with it on, and have not seen any problems. The consensus seems to be, that if your transmission isn't "hunting", then you can stay in OD.

I have my Edge Evolution set for the "tow mode". and it alters the shift points and other goodies.

When I went to the rally in July, I had no problems at all.

Your mileage may vary.

No straight answers here.

Good luck and Happy Camping!

[pershingd]

Good point about checking the owner's manual.

You're absolutely correct about there being no straight answers here. It really boils down to whether or not you're comfortable towing in OD or not. Personally, I hate it when the transmission hunts up and down and cannot maintain a constant speed (within reason   ) so I shut off the OD and I'm happy. I'd be happier with a manual transmission, but my left knee doesn't like it too much   .

David

[zamboni]

My Explorer manual says to keep in OD unless it is "shifting excessively".

If the drive is flat, OD is no problem.  In fact, yesterday I had cruise control set at 55 (instead of me micro-managing the accelerator like normal).

We got 13 MPG instead of 11.5 without cruise control.  I am now a convert.  Of course, I turned off CC and OD in hilly areas, etc...

[pershingd]

The only time I can outmanage the CC is on the hills here in the Ozarks when I'm running empty and in OD. The CC will shift up a gear to keep the speed down on the downhill side and then have to get back on it hard up the next hill which evokes a big upshift (all the way to 3rd).

With only 4.7L and a double OD automatic (4th - 0.75:1, 5th - 0.67:1) its no surprise that the hills and towing throw it off a bit. It also explains why towing in OD isn't the easiest thing either. When I'm in OD the effective final drive ratio is 2.63:1  :eyecrazy: - not exactly a towing friendly gear ratio. If I could lock it in 4th (which I can't) I would still only have an effective ratio of 2.94:1 - still not at all friendly.

David

[wavery]

The other variable, not discussed, is your towing speed.

OD is basically designed for your engine to run at a lower RPM at higher speeds. The overall gear ratios in the vehicle (not just final drive ratio) are carefully designed, taking into consideration the weight of the vehicle, HP, wind resistance, tire size etc. When you change any of these factors, IE towing, you change the effectiveness of the OD.

In California, the speed limit for towing is 55MPH. I would not recommend towing in OD at 55MPH for any vehicle. Basically, there is no upside to it. Even if your vehicle is not "searching" (switching in and out of OD), the engine is running at a lower RPM thus putting out less available HP (the higher the RPM the higher the available HP). As mentioned previously, the throttle must be opened farther to achieve the same speed in OD than it would be if you were out of OD thus demanding more fuel.

For those of you that tow at 70MPH on flat land, those factors change slightly but I doubt if it makes much difference in your overall fuel consumption. OD is designed for a vehicle with a minimal amount of weight driving at maximum highway speeds to be effective.

[CAPEd CODger]

The other variable, not discussed, is your towing speed.

OD is basically designed for your engine to run at a lower RPM at higher speeds. The overall gear ratios in the vehicle (not just final drive ratio) are carefully designed, taking into consideration the weight of the vehicle, HP, wind resistance, tire size etc. When you change any of these factors, IE towing, you change the effectiveness of the OD.

Another good point. I usually tow at 55-60 MPH.

Staying out of OD will keep the engine in the "power band" where you get the most HP and torque.


Going to and from our last trip, we went over South Mountain, MD and Braddock Mountain, MD on I-70. No OD there.


The Baltimore Beltway has a lot of rolling hills, too, and as much upshifting and downshifting was going on, I decided to keep the OD off.

Made for a better drive, but at the higher RPM, the gas milage tends to be poorer.


Happy Camping!

[zamboni]

In California, the speed limit for towing is 55MPH. I would not recommend towing in OD at 55MPH for any vehicle. Basically, there is no upside to it. Even if your vehicle is not "searching" (switching in and out of OD), the engine is running at a lower RPM thus putting out less available HP (the higher the RPM the higher the available HP). As mentioned previously, the throttle must be opened farther to achieve the same speed in OD than it would be if you were out of OD thus demanding more fuel.

Coming home from Pismo, I decided to test this theory -- when I got back on the very flat central California valley floor.

At 55 MPH, towing the big hybrid (much more air resistance than older popup), I alternated 10 miles in OD and non-OD.

Consistently, being in OD gave me about 1+ MPG better - 12-13 versus 11-11.5ish (OD gave 13 if it stayed, dropping to 12 average if overpasses required occasional downshifting).

However, if I tried to bump my speed up to 60, it would never go into OD, and my mileage dropped to about 10 when I averaged about 62.

Food for thought.  On a 300 mile drive, do I want to get there 35-40 minutes faster and $15 poorer (5 gallons at $3/per, assuming 12 MPG with OD)?