I have an 01, F250 7.3 liter diesel, on flat to modertly hilly roads no question the O.D. is on  along with the cruise control.  This past weekend we went to a new campground, had to travel over some large long hills. I just kept everthing as was and let her go, it did do some down shifting in order to keep up the speed, which it did (keep the speed up that is). However my better half kept saying I had better kick the O.D. off. That begs the question when do you know or when is the time to take it out of O.D. what is the rule or general guideline??? Should I take it out if it is down shifting once every two minutes ?? when it starts down shifting from third down into second?? Maybe kick off the speed control and try and control it that way? Or as I told my wife, hey that is what I bought it for and keep on truckin. I must admit, most of the time I listen to my wife, I'm like Howard I married way over my head, so I have a feeling I should follow her advice, but my (male) way of thinking is what is the advantage of a diesel if I have to baby it.  Please advise.

 Flyone

Hi Flyone,
Overdrive is just a higher gear to save fuel when your at highway speeds, but it will downshift by itself, as soon as there is any strain on the engine.
Ialso use my cruise control almost all the time on the highway, if I'm not in heavy traffic.
I let it do what it wants and it seems to handle just about everything effortlessly. I especially like the fact that it automatically downshifts to prevent over speeding when coming down hills.
I feel that cruise control makes long trips painless. I just set it at a few miles less than the speed limit and relax in the right lane.
Fred

O.D. is just that, a overdrive, if you are in a pull it will downshift, however leaving it in O.D. it will want to upshift when it can, and if you are in hills where it is shifting back and forth that's where you'll get in trouble, heat will build because of the  shifting back and forth. As for just letting it go, you really need to watch your rpms any motor will lug but that doesn't mean it's good for it. Read your manuel and find what rpms they say is your peak torque, keep it in that zone and you'll be a lot happier in the hills. Good luck! 

New transmissions with towhaul mode work great.  We do cut out the OD in windy or hilly tow conditions but the reality is that towhaul mode would probably downship on it's own.  We have also figured out that cruise control is smarter than we are except when going down steep grades.  Again new transmissions downshift when you brake heavily in towhaul mode.

Larry

 

Flyone

I think most of the posts are from folks with newer trucks than us (Towhaul). 

I have a 99 F350 with a 7.3 diesel (20,000 lbs total rig). I leave the transmission in overdrive all the time when in "flat & climbing" conditions. The only time I turn off the overdrive is when I want to hold my speed while "decending". I live in Central California and often camp at Shaver Lake which 5,500' in altitude. The road grade is 6% and I can decend the hill holding 55 mph by just taking it out of overdrive (no brakes).

As for the cruise control. I never use it in the mountains...

Brian

We drive a 2000 Chev 3500 Crew Cab dually 7.4 gas 4 speed automatic.  Before retirement, we had a full service automotive repair business (for 40 years).  We saw many transmission repairs and investigated the situation with dealers and transmission shops.  Their instructions were to NEVER pull ANY trailer in OD!  Shift down to 3rd for regular over the highway towing and for hills/mountains etc, shift on down to second and first if needed.

Just our many years of experience and opinion.  But, you should at least check it out with a knowledgable dealer or mechanic.

 

Here's a quote from the October06 Motohome magazine which provides additional very credible info on this topic and supports some previously mentioned posts.

Tips From a Retired Engineer (Edward Hayes, Brighton, MI)
I worked at Ford Motor Company for 24 years in research and development for powertrain and am now retired. I would just like to reply to the letter from Kristi and Steve Burns ("Our 'Vue' on Overdrive," June) concerning automatic transmissions.
You are so correct in advising that the driver should manually shift down from overdrive to third gear if the engine is hunting. The overdrive gear set could probably handle the load, but the clutch pack will suffer and the oil temperature will rise. Pulling too hard in any gear will force the torque converter to unlock, producing high oil temps. Also, running the engine at higher RPM will pump more water through the engine, thus reducing hot spots in the head, and it will circulate the engine and transmission oils at a faster rate.
Edward Hayes, Brighton, MI

Again, the above came form Motorhome magazine, October06. 

 

-- Edited by RVDude at 13:10, 2006-10-25

-- Edited by RVDude at 13:12, 2006-10-25

I had a 2001 Dodge 4x4 truck when we pulled our TT & the manual said to take it out of OD when towing so that's what I did. It made sense to me at the time thinking I would have more control of the shifting seeing how it would be trying to get to the higher gear faster if in OD. If I'd forget to take it out of OD I would think something was wrong with the transmission right before I realized I didn't switch it out. Never had a problem with it hunting for gears & the fuel milage was comparable to others towing so that's why I thought that was the way to go.