I'm new to towing and new to my '02 F350 DWD. Last week was my first road trip hauling my 44' enclosed toy hauler. The trailer loaded with two cars and track gear is about 15,500# - calculated from a combined weight of 23,334# and a truck weighed in at 7,880#. It pulled beautifully, but my BMW mechanic recommended not using OD, so I ran the 300+ miles north on US95 to Richmond VA (mostly uphill slight grade) with it off. After searching here the consensus is that OD with a load is fine, but only if it's not downshifting.

The tranny temp gage on the pillar wasn't hooked up by the previous owner just the EGT and boost gages (it's on my list of things to do) but the tranny temp on the dash works. Half way through the trip out, the dash gage went high (just below the top of the gage (below yellow and red marks). I have no idea what that temperature would be. Anyway I backed off on speed and it came back down to mid gage. On the return trip I left OD on and didn't have any temp issues (but it was mostly down hill coming home).

My question is did driving 70MPH with OD off cause the high temp or would it have gone high with OD on? Do I need an upgraded tranny cooler? I'm still feeling out this setup so I appreciate the input.

 

I believe a better Trans cooler is always a good idea.

 

Don't trust the idiot gauge on the dash. Hook up your pillar gauge so you can monitor the real temps. An auxiliary or upgraded cooler is almost mandatory to extend tranny life since the stock cooler is a bit undersized.

What chip or tuner do you have in the truck? What setting did you have it in for the trip? What kind of EGT readings did you see while towing?

 

That's a big trailer!
I drive a ZF6 so I don't have a lot of personal experience with the automatics but I think that the answer to your questions at the end of your post is yes to all of them.

 

that s a big boy load. i would think cooler.

 

I wouldn't say I trust the idiot gage other than 'ballpark' this was the first time it moved outside of middle range. I'm motivated to hook up the gage now.

The gage is getting hooked up and the cooler isn't expensive so it's going in soon (any recommendations?)

It's got an old version of a Quadzilla. Not sure what the settings are, there is just a four position **** on the dash, no documentation, and no idea what it's doing. Pretty much just leave it on the lowest **** position.

 

One thing I really noticed with my dually when pulling a my trailer (half the weight of yours) is the trans temps are good at freeway speeds usually on somewhat level road.. But.. if you come into town with a few hills and stop lights, the temps will go up real fast.. the torque converter is working harder.. Be sure to get an aftermarket temp gauge soon..!!
If you are on level road, I would think OD would work just fine.. It will downshift automatically if it needs too..

 

I think there is more square footage in that trailer than the home in the picture behind it!

 

I strongly recommend a supplemental cooler and try and hook up your gauge before your next tow. For me, the general rule of thumb is to climb a hill in the same gear that I would use to descend that same grade. I usually don't head downhill with that kind of weight in OD so I wouldn't have it on going up either. You might have 4.10 gear set so you might benefit by using OD as much as possible. The general idea is to use OD (normal mode) by default and turn it off when you encounter a modest grade (uphill or downhill). In addition, if you are pulling a really steep grade, you might want to pull down to 2nd gear instead of letting the trans shift between 2nd and 3rd and back down again because that will get the fluid hot pretty quick.

I notice cooler temps when in OD and TC is locked. I have yet to see my TC lock when in 3rd gear, I am told these transmissions will lock the TC even in 3rd gear but I haven't seen it happen with a heavy load in tow.

If you have a choice, you will get a more accurate temp reading with the sensor in the test port vs the pan. It takes too long for the fluid in the pan to warm up and register a meaningful temp.

Happy towing!

 

I have had good luck with TruCool brand coolers. I think they have a model called TruCool Max that looks nice. I like these better than a 6.0 cooler because they are easier to install. I prefer my supplemental cooler to be located in front of everything else. However there are lots of members here who have 6.0 coolers that work out great as well. Your choice.

 

Hey Greg, don't know about your '99 but on my '01, if you'll tool along say at least 40mph, push the OD button to off, it'll be locked in 3rd. You can tell because when you let off of the go pedal, the R's will fall slowly along with the speed.

Yours won't do that??

 

Get the tranny gauge hooked up. Flush the tranny per Mark K's. procedure. Install another tranny cooler.Before my tru-cool, I would see @ 205° and factory never moved.

 

Running at 70mph on a flat highway, you should have your OD in the standard 'ON' position. Having it off at those speeds is what got your tranny temp up. If you are running up grades and corners at a constant slower speed, that would be the time to have the OD off.

The very best thing to do is to get a 6.0 trans cooler in it.

 

How many RPM were you running at 70 MPH? Had to be a bunch. lol

 

I have an LED on my dash that illuminates when the PCM locks the TC. I don't know why I installed the light...was just fooling around one day and did it. This is how I learned that in normal driving (without a trailer), the PCM would automatically unlock my TC every time I touched the brakes. I do think you are correct and the programming may have changed in the later years. Maybe someone with programming knowledge will chime in on this topic...

Next time I'm dragging around my trailer, I'll try what you said and see if the light stays on when I cancel OD. Now that I think about it, I never really turn off the OD unless I am getting ready to climb or descend a hill. So what normally happens is I turn off OD and roll into the throttle to begin climbing, I assume the PCM would not allow the TC to lock under those conditions.
(If I am about to head downhill, I would have my TC locked manually before I turn off OD and pull down to 2nd so that explains why I am unable to tell if the PCM locks the TC or if I am forcing the issue.)

In the OP's case, if he was running around in 3rd gear with that kind of load...I bet the TC was locking and unlocking every time he rolled in and out of the throttle. To me that seems like a good way to get the trans fluid nice and toasty. With the OD enabled (normal mode), you have to really get into the throttle before the PCM will unlock the TC. (assuming highway speeds).

Around town, I just leave OD turned off because of the nature of stop and go driving, it's nice to have the OD disabled so the transmission provides a little extra engine braking. Nothing worse then approaching a stale green light with OD enabled and 16.5k lbs in tow....if the light turns yellow and I jump on the brakes it feels like the PCM let's the TC unlock and I don't get hardly any engine braking to help me stop. In fact, it feels like the transmission falls into neutral gear and the engine just drops to idle (sort of like pushing in the clutch on a manual trans vehicle). In contrast, with the OD disabled, it feels like the transmission hangs in there for a while while I am on the brakes and I can really feel the difference it makes to have some engine braking. Eventually though, I slow down enough that the PCM has to unlock the TC or the engine will stall so I've learned where that point is and come to expect it. I guess we all learn the little quirks of these trucks as we pile the miles on the odometer.

Hopefully some of this info will help the OP out and he'll have many many miles of safe and happy towing.