I don't know how you would get Ford to tell you that, but it is possible that Ford or the transmission's design company engineers have written an SAE technical paper about the design of the transmission. Such a paper might have something to say about the heat resistance performance of the transmission.

Regardless, Ford maintenance recommendations are that no fluid change is needed, nor is checking the fluid level. Either that is significant confidence in the design, or wanting to make sure that the wrong fluid doesn't get used. It uses the almost unobtainable Mercon V.

If you are really concerned, you can always add another trans fluid cooler, however, you would need to add fluid to account for the capacity of the cooler and any fluid lost. There is probably a way to do that; I haven't looked that up in the shop manual, though.

 

Rich, if you've got the shop manuals, does it say anything about the conditions that would set a high transmission error code? My prior vehicle was GM, and per the shop manual the tranny high temp code would set at something like 285°F for >10 minutes (yikes!)

Is the Mercon V a semi-synthetic or all synthetic fluid? I would expect the 'old chart' for transmisson life is for non-synthetic fluids. Obviously high temps are bad for the tranny itself, but the fluid should be able to higher temps.

 

Ford maintenance schedule calls for replacement of the transmission fluid every 30,000 miles in towing service. But only every 150,000 miles in normal service.

I expect occasional towing won't require a 30K change but it's inexpensive and at these temperatures I'd sure to it!

-- Chuck

 

I can add some data points since adding a Dashhawk:

2007 Expedition EB standard-length
4x4
3.73 gears
HD Tow (added the HD Radiator and 7-row TOC after the fact, but they are genuine Ford parts)
Starcraft 26SK trailer. Let's call the whole rig 13,500 lbs or thereabouts including family and gear.

I tow in Colorado, so add roughly 7-10 degrees to the ambient temps to equate to sea level or thereabouts, due to the reduced heat transfer of lower density air.

Ambient temp: 85 deg.F.
Freeway towing (I-25 north of Denver) 72 MPH
Coolant Temp: 198 degrees on the flats, as high as 208 degrees on the 2-3% or so grades, maintaining speed.
Trans fluid temps (under the above conditions) 200 degrees on the flats, 215 degrees on the slight grades.

Pulling Cameron Pass (roughly 3-4% average grade, max elevation 10,275, ft 55 MPH), ambient temp was about 75 degrees
Coolant temp reached 230 degrees (stable)
TOC reached 234 degrees (stable)

One thing I've noticed on cold starts is that the transmission oil temp readout on the Dashhawk is about 7 degrees higher than both the coolant temp and the outside (ambient) temp readout. I'm wondering if an offset was added by the Ford programming folks for some reason.

Without the trailer, coolant temp is 192-194 degrees and the Trans fluid temp is 185 degrees.

Dakota123

 

230 degrees coolant temp?

 

230°F coolant & 234°F TFT seems pretty high. At 75*°F ambient, do yo still have the A/C on? Even if its on a little bit, its adding extra heat. Personally, if I started to get above 225°F, I'd start slowing down, select a lower gear and turn of the A/C, and even turn on the heater if the temps continued to rise.
Have you weighed your rig? Most people find they're heavier than their estimates.
Dakota, you can set alerts on the Dashhawk to warn you as certain parameters (temps) get to high.

 

I should have added that the temps peaked after slowing to allow a vehicle to turn off and then accelerating back up to speed. Once getting back up to speed the trans oil temp dropped to 225 or so.

I frankly was pushing it. After adding the super-cooling parts I wanted to see whether I was out of the woods. I'm not completely satisfied; I believe that the fan clutch isn't hooking up reliably. With my 2005 Expedition I would hear it pretty regularly. I hardly ever hear it with the '07.

Also, someone asked what Ford considers to be the max continuos trans oil temp. I don't have an answer specific to the 6R80/85 but I found one source, when discussing the 4R100, that Ford considers 240 degrees the max allowable. http://www.roscommonequipmentcenter....notes/nn15.pdf

Finally, the trans fluid is Mercon V SP, which is not the same as Mercon V. Checker carries it.

Ciao,

Dakota123

 

Dakota, I remember reading that article a few years ago when I was battleing problems with transmission temps with a van I had at the time. I ended up adding a Derale electric transmission cooler with a thermostat controlled fan underneat the van body. That really helped keep the transmission cool without adding extra heat to an already crammped and hot engine compartment.

 

Interesting...