1995 F350 PSD Dually Crew Cab AUTOMATIC

I have a towing question for you guys. I have a 32 foot fifth wheel Toy Hauler weighing in at around 11830 GVWR, 7000 unloaded.

Everyone says to tow with OD (overdrive) off. That means I will turn about 3000 - 3400 rpm's at about 55-60 mph. That's screaming. And then I look up and someone with a larger trailer than mine blows past me like I'm sitting still. How can they run so fast? My engine will blow up if I push it an harder.

Is it OK to run in OD say 65 - 70 on flat ground if it is not changing gears? Some people told me that even if it is not changing gears at higher speeds with a heavy load the tranny is still slipping a little even if I can't feel it and that long term towing like that will burn uo the tranny. I was told with the OD off the tranny hooks up on a 1:1 ratio and will not allow any slipping.

Any comments?

 

Everyone that says always tow with OD off is wrong.

In overdrive or even in third gear you can run with the torque converter unlocked which will generate A LOT of heat. It is more likely in overdrive.

Learn what RPM you run at towing speed in overdrive without the trailer. If you are in overdrive and running more RPM with the trailer on your torque converter is unlocked. That will get the trans hot.

Most likely you won't have any problems towing in overdrive.

 

If you haven't already ... get a reliable trans-temp gauge and the best/biggest transcooler that will fit . The use of synthetic fluid will help the transmission live longer too .

 

Actually the RPM's are just a little bit less (2900 - 3200) than that but still screaming when towing with OD off.

 

If you can run in OD without the tranny hunting (constantly shifting in and out of OD)
you should be ok just keep an eye on EGT and tranny temp.
As long as your RPM is over 1900 you are in a good area of both power and torque curves; however, if you get over 2300 you start to lose power and torque.

I suspect you are running 4.11 rear end maybe even lower, the don't tow in OD advice is aimed at those folks with 3.55 or 3.73

 

Of course you can tow in overdrive. Thats what its for. The guys above are right about torque converter lockup, frequent shifting in and out of OD, and low ratio differentials. Whichever rear end ratio you have, you will learn what kind of road grade will result in frequent shifting, and you should punch it out of OD till the road levels. You will also learn to anticipate the grades coming up, and punch it out of OD manually rather than wait for the automatic downshift. This is just to avoid accelerated clutch wear in the tranny; some amount of shifting is expected, and the tranny won't self-destruct when it happens. There are two ways the tranny can "slip". The internal clutch can slip, and of course does slip as it engages. It won't slip once the gear is engaged as long as the tranny is turning at more than idle speed and the tranny oil pump is working normally. TThe most important point is with regard to torque converter lockup, no matter what gear you tow in. You must learn to recognize the behavior of the tachometer which shows when the torque converter locks up, no matter what gear you are in, and make sure that you don't drive under heavy load (towing) for more than a few minutes with the torque converter unlocked. The torque converters typically lock up at about 40 - 45 mph. That torque converter slippage really generates a lot of heat in the transmission, and even with an auxiliary tranny oil cooler the oil can get overheated. This is important. Get a set of guages to monitor tranny temperature, exhaust gas temperature, and boost. Learn how they behave under various conditions. watch carefully on steep grades or low speeds where the temperatures go up. Don't hesitate to pull over to let the temperatures come down. Too bad if you hold up traffic; YOU will foot the $4000 for a new tranny, not guys behind you. Synthetic oil is good because it conducts heat better, making the tranny oil coolers work more efficiently so the oil runs cooler, and the synthetic withstands higher temperatures without breaking down like the fossil-based oils. You can therefore run it at a higher temperature, and run longer between oil changes. Whatever oil you use, learn the operating temperature limit for it and don't exceed it. The bottom line is you can tow in any gear, with any differential ratio, with any kind of oil, with any kind of tranny cooler. You just have to learn and respect the limits for your particular set of conditions. And if you don't have guages you won't know where you are till its too late.
Happy Towing
Warren