What is your engine and transmission technique for towing?

[GBrock]

When I had a F450, it had a 6 spd manual transmission that would outlast the truck and motor (wish I never sold that rig). Hence, I rarely worried about leting the transmission do the work. Now that I am driving a Cummins mated to an Automatic (99 2500 with the auto trans), I am trying to determine how best to manage the workload. There are times you turn the O/D off and let the motor do the work... other times I am told it is OK to let the trans do the work and run the motor at a lower RPM. Chirs at Relentless Diesel tells me to keep the RPM above 1700. If I have to go below 1700, then I should turn O/D off. He knows his stuff so I am following his advice. However, I have noted w many owners commenting about how they turn off their O/D everytime they tow heavy.



So what technique do you use? When is it OK to to in O/D and when not?



I tow a 11,000 lb boat. If I am on a longer trip, the load on the trailer can be as high as 15,000 lb.

 

[Fireman Dave]

Well, here goes. I tow with OD locked out most of the time. With my 3. 54 gears, the RPMs are just too low for my liking in 4th gear. Some guys here are fine with towing in OD. When I first got my truck, I had a conversation with a well known transmission guy who's opinion I respect a lot. He said 1 to 1 is best for the transmission. That means 3rd gear for us. I've also heard the same advice as Chris gave you about 1700 RPMs being a boundry. I agree with that based on my experience towing. My truck just doesn't seem as happy at 1700 or 1800 as it does at 2300. I have towed in OD on very flat stretches, but those usually seem few and far between.



Here's a couple of other factors that enter into it too. My truck has stock power, and I don't tow over about 60 mph. The latter is due to my belief that faster speeds increase the chance of trailer tire failure due to heat. I know a lot of guys tow faster. For me, I prefer to be a little more cautious, I guess. I change my trans filter and fluid every spring. My truck has 65,000 miles on it - probably about 15-20,000 of those are towing miles. I haven't had any transmission problems to this point.



Some of my local TDR buddies like to tease me about the OD thing - which is getting old, by the way. But it works fine for me. I figure the transmission guy I talked to knows a lot more about transmissions than those guys do. I guess I just don't have a problem taking it easy on my equipment - even if it does bother some people for some reason. If they want to call me a granny driver, then fine. But I'm not the one on the side of the road broken down, either.

 

[gwagner]

the way i see it if it works for you keep doin it. don't worry what any one else says. Its your truck and your money. just shrug it off and keep on keepin on. just my . 02

 

[GFrance]

I'm with you Fireman Dave. I too tow at 60to 62 max overdrive locked out. Never in that big of a hurry when vacationing. With 3:54's seems like you have to be up around 68 mph to be in the sweet spot & some states have a 55 mph limit when pulling a trailer.

 

[rweis]

I do 62 / 2400 w/ 3. 54 O/D out. I have a high profile 5er. I did the DTT transmission at 20k. Before I did the Dtt I was very careful to keep the rpm up in the 1800 - 2000 range for sufficient transmission pump pressure. When Dtt opened up the transmission there was not any internal damage at all.



Bob Weis

 

[jtisdale]

My local TDR buddies like to tease me about the OD thing - which is getting old, by the way.

Not all of us Dave.



I dont have an auto (6 speed w/3. 54) and I also keep my rpms around 2000. So, most of the time I am towing I keep it in one to one (5th). Doing this it keeps the boost up and egts&coolant temps down, at least with my set up. I have also found this helps a lot with mileage.

A friend of mine just bought a 1986 30' bumper pull Prowler camper. Him and I went to get it yesterday. It was 120 miles down (empty) and 122 miles back (different route). He paid for fuel, so I topped the tank off before we left, and topped it off when we got back. Mileage... average 16. 5. Speed average... 47. 4 (including time stopped of almost 1hr).



Somewhere on the Cummins website is a rpm calculator. With the isb engine they claim best rpm is at 2000-2100 rpm. Thats where this engine is designed to run the most efficient. But, with gearing and speed being factors, maybe sometimes it isnt easy to keep the rpms in the "sweet spot". Besides, even the owners manual doesnt recommend towing in OD with an auto.

 

[cwsoules]

I tow in OD on flat land at 62 mph in cruise control. My DTT smart box prevents the transmission shifting to OD until 57 mph. I watch my gages if the EGT exceeds 1200 I slow down to keep it there or lower. If the mph starts to drop and the EGT rises I will shift out of OD before the transmission shifts down at 57 mph. I try to shift down befor the transmission does it in automatic. I watch the speedometer, EGT and transmission temperature as a matter of routine.

 

[woodsrat]

Load'em like boxcars drive'em like stock cars fix what ever blows first

 

[ndurbin]

I tow in OD until the motor begins to bog down on a hill, then I turn OD off and finish pulling the hill, and back to OD afterwards. I also always keep the RPMs over 1500 in OD. I hate towing w/ OD off as my truck defuels past 2200 rpms so I can only run about 55-60 w/ it off.



Nathan

 

[Eric_77]

My course of action is ease into the throttle 1/3-1/2 until RPMS are above 1700RPM then put it to the floor. The weight I pull is pretty constant at 23,000 GCVW on a cargo trailer (33'longx8'widex 8'6"'high box actual from ground is 10'3") I run around the speed limit and if I see a hill coming I will goose it up a bit to get turbo spun good and if speed starts dropping where RPM drop below 2000 I downshift it. I run the same route so I know which hill I need to downshift for and prepare ahead for them by downshifting. My 96 defuels early (like 2400) so I cannot spin the engine fast so I have a 1900-2300 spot I run in all the time. The 03 I don't even worry about it, never hit a hill that it needed to downshift for but I live and drive in Texas.