I have a 2002 F-250 with the tow package and i'm pulling a trailer this summer from California to Michigan and was wondering if the factory trans cooler is adequate. Truck has 45,000 miles and since new I have done the trans valve body, replaced the filter and serviced the trans twice and did a flush and put in mobil 1 trans fluid.

 

Your factory tow package cooler should be more than adequate. Just be sure to get out of O.D. when in the mountains, also an oil temp gage might be a good idea and if it starts to spike, pull over and let it cool a bit.

 

Depends on size and weight of trailer, and your driving options....

My experience:
'99 with V10. The '99 gassers originally came set up without the trans fluid going through radiator. Instead, they had a very large stand alone cooler. I've read that it was bigger than the ones put in the diesels and later models.

I live in California, and frequently tow over Donner, Siskiyou, and several other long, demanding, and high passes. And sometimes at temps over 100 degrees.

Experience told me that the stock setup would never make it. So I:
1) Installed brand new radiator from later model so I have trans cooler in radiator.
2) Added yet another auxiliary cooler, the great big one from B&M, between the condenser and radiator.
Fluid routing is: From trans, to stock standalone, to radiator tank cooler, to B&M, to trans. I used steel pipe and oversized fittings and hoses wherever possible to minimize flow restrictions.

The results:
I tow a pretty heavy travel trailer with minimal frontal area (Nash 22H), but also haul a lot of toys. I'd guess about 9000 pounds.
On a 100 degree day, the trans fluid still peaks out just over 250 degrees (measured as it leaves the torque converter, using the stock fitting in trans case) at the tops of the big grades. I use only Redline high temp ATF, even still, I would pull over at 260 to allow it to cool - so I'm nearing pull over time even with my triple cooler setup.
On a 60 degree day, closer to 225 degrees.

A lot of my buddies choose to pull the grades at night for this very reason.

So what is the frontal area of the trailer, and how heavy? And can you do the big grades at night?

By big grades, I mean ones like Donner or Siskiyou or Vail... 8%+ for 15 minutes or more.

As a minimum, definitely get the temp gauge installed.