Towing in O/D on interstate

[merc123]

My 2000 F350 is rolling over into the 145k range and was thinking about the transmission. I bought the truck with 95k miles and did a trans fluid change at around the 110k mark. It wasn't burnt but it was a little dirty. The current fluid is still a pretty red color. It shows no signs of issues that I can tell and runs around 125*F unloaded in the summer time and around 150*F loaded with an occasional 165*F loaded at slow speeds through the mountains.

I've got a race track I go to that is 95% interstate and mostly running "up" the mountain most of the way. I try to run around 75 to 80 so the truck doesn't bog going up the hills (I'm within the speedlimit...). If I get behind a car and I'm running 70 it can slow me down to about 55 going up a hill while trying to keep my EGTs below 1200 and boost sticking around 10 to 15 PSI. Trans temp in the dead heat of summer only runs around 150* on this particular run.
I'd say the load is about 5k with trailer and around 1k in the bed. Truck is 8k with full tank of diesel and two people in the front seat so around 14k total.

I don't find the truck hunting gear at 70 MPH (even dipping down to 55) it won't try to downshift. It just keeps chugging right along. On the way home which is coming down in elevation I see hardly any problems keeping the speed at 75 the whole trip so it definitely doesn't search for gears.


Should I go ahead and just keep running it with the O/D on or should I turn it off?

[7.3550Duty]

Well if your truck isnt bogging down at all and your running at 70, i wouldnt even worry bout it at all. Now maybe if you had like 12k behind you, then i prolly would say ya watch your egt's. You should be fine. If you make that run alot, maybe look into a 6.0l trans cooler to help out with cooling and get yourself a valvebody kit. That will help out with a few things wrong with these trannys.

[merc123]

Cooling isn't an issue with the Tru-Kool cooler. I was thinking of getting the BTS valvebody kit. Would reallylike to just get the entire BTS transmission and call it a day.

[7.3550Duty]

Yeah i hear ya, i had to replace my trans at bout 118k. Yeah a VB kit will help out quite abit from what i heard and read. BTS or JW VB would be your best bet. And if you can afford to swing it, pick up a Torque Converter, that may help out even more.

Where did you pick up your tru cooler? I didnt replace my cooler when i replaced my trans, just had it flushed out. How big is that tru cooler compared to a 6.0 cooler??

[SuperCrutyPS]

I agree you can stay in O/D as long as your truck isn't bogging down or the transmission isn't gear hunting.
I run O/D on when towing my 12k 5er on the flats, but turn it off when doing grades.

[merc123]

I got my Tru-Cool 4739 from the www.dieselsite.com but it doesn't look like they carry it. It was $141.59 to the door. Half the cost of the 6.0 cooler.

Here's a picture (and my thread on it). Pretty much the width of the vertical and horizontal grill slats. I just drilled through the vertical "bars" (fiberglass?) and put bolts with lock nuts through them. I didn't use the "factory" hardware that came with it mainly because I don't think I could figure out how it was supposed to go. I think I used a 3/8" or 7/16" by 1" bolt and lock nut.

Tru-Cool #4739 transmission cooler

[7.3550Duty]

Yeah doesnt seem to bad for price at all. Seems like a steal to me. I may have to look into that this year. Dont do alot of towing really but it would be nice to know when i do tow that i have adquate cooling for my trans, didnt spend all that money for nothing right??
Now did you just tie into your existing trans cooler or just completely replace your stock tranny cooler?? Ive heard people just tying into existing and just adding but if it was me, i would just replace the whole thing.

[merc123]

It was designed to actually run in series with the stock cooler. You actually tie into your transmission lines and not the stock cooler so it may not work right by replacing the stocker. Plus it just adds to the capacity to cool. Aside from towing, it still really helps to keep it cool unloaded. Big tires can heat it up unloaded also.

[goats]

I say if it's not trying to change into the lower gear just leave the OD on. When it keeps upshifting and down shifting is when the tranny temps heat up.