I know this has probably been discussed on here before but I have been unable to find a strait answer on the subject. I have a 2004.5 auto with the 3.73 gears and 285-70\17 Toyo open country A/T's. Is it ok to tow in Overdrive? As i understand it the 04.5's Tow/Haul mode is just an Overdrive Lockout. If i pull my 8500 lbs trailer at 65 in OD I am running about 1700 RPM if I lockout OD i am running about 2500 RPM and my mileage takes a dump. Am I going to damage something by Towing in OD?

 

I would pull an 8,500 pound trailer all day long in overdrive.

I pull my 14,000 pound 5er in OD, but I don't have an auto tranny. I may be pushing it a bit, but I don't think you are pushing it at all with that kind of weight.

I say you are good. I'm sure others will have different opinions.

 

Your fine til you get to 12k-14k. Even with that might be fine on flats.

 

As I understand it the HPCR makes peak TQ at 1600 rpm, What is the lowest rpm I should be towing at?

 

Ideally you should try to keep it around 2000 rpms, in my opinion. But that is hard to do towing....sometimes.

In O/D you would be running 75 or so....which is a little fast, towing.

To answer your question.....NO it doesn't hurt to tow in O/D. I tow in O/D all the time. But if I find myself slowing below 60-65 or so I do put it in tow haul...which locks out o/d. It will then shift down and give me some rpms and cooler egts.

It also doesn't hurt to run it in 3rd either......up to 3000 rpms. But like you said, your mileage suffers.

So my experience is..............I keep in in TH mode anytime im towing starting off or below 65 or so. If im on open flat highway, I try to run in O/D....at around 70-75. I watch my EGT gauge and try to keep it below 1000 degrees....or maybe 1200 on a hard pull...up grade etc.

I also tow with my Smarty on....which helps it run cooler and gives it extra power on hills etc.

..

 

Nope, at 1600 rpm's you are at about 40% defuel. It won't pull there unless you modify the ECU with a programmer.

The BSFC on a CR is about 1900 rpm's, under 1800 rpm's the fueling ramped sharply down. You want to tow in the 1900-2100 rpm range for best results.

Tow all day long in OD as long as you can keep the rpm's in an acceptable range. Run them high if you have to in slower moving traffic, it will help keep the injectors clean.

 

I try to keep my towing at 2000-2100 rpms.. The only bad thing is that I'm a little over 70mph when towing the 10,000 fver.

 

I tow all the time in OD in the flats, when I hit the hills/mountains I push the button. I tow a flat trailer with my rock crawler. The combo is about 7,500 pounds. I have about 62,000 on the clock, no problems so far. No mods, stock sized tires.

 

Just listen to your truck. It will tell you when it's happy.

 

Towing in OD won't hurt the tranny unless you are putting out more power than stock. Then you will slip the stock TC.

Also the engine, at lower RPM has higher EGT and less throttle response. As Texas said, get it up to 2000 RPM or so and everything is better.

So, it's not a matter of "can we" so much as "should we". Flat ground OK, hills or passing, not the best idea. Make the engine and the tranny happy, tow in Tow/Haul at 2000 RPM or so when you are really working it. OD if you are coasting or on level ground. And remember, the TC locks up in Tow/ Haul and the tranny, in 3rd, is the most efficient with no extra set of gears being used for OD.

It amazes me that a Cummins will do just about anything you ask it to. It's not like you have to keep it to the wood at max RPM like a gasser. But sometimes you just know it would be happier with a few more revs.