700R4 - Loss of trans fluid when a) 60mph b) towing boat up hills

[6wt]

84 C10 / 350 / 700r4:  Transmission is leaking copious amounts of trans fluid out of the torque converter cover area when towing my 2500# boat down the highway at 60mph.  And, really loosing trans fluid when i go up rolling hills out on the interstate.  These are hills with no more than 300ft elevation gain.  I believe the trans is shifting out of OD, but i do not know if the trans is downshifting past DRIVE (ie. 3rd?)

I lost 1.5 quarts of trans fluid yesterday on a 125 mile trip to the lake.  I got lucky and noticed it when i stopped for gas.  I put new fluid in and continued on my trip at a reduced speed of 50~55, and no significant hills.  Arriving at my destination i did not see any noticeable loss of fluid; but still had a few drips from the same area.  Prior to this trip, when driving around town towing the boat at 50mph and slower i am not noticing any loss of fluid or drips.

What is going on?  What happened?

Any help is appreciated as i need to address this before driving on the highway/interstate again.

[VileZambonie]

Are you running an auxiliary cooler? How is the fluid condition?

[6wt]

I do not have an separate aux cooler.  But, there are trans lines to the radiator for supplemental cooling of the trans fluid.

At the time of the substantial fluid loss, ie rest stop, the fluid had a slight brownish tint to it; but did not smell burnt.  The color and smell of the trans fluid are normal now; ie looks and smells just like out of container.

Drove 30 miles in-city yesterday, averaging 40mph with some cruising up to 50-55 for 1-5 miles.  No fluid loss detected.

[VileZambonie]

I do not have an separate aux cooler.  But, there are trans lines to the radiator for supplemental cooling of the trans fluid.

At the time of the substantial fluid loss, ie rest stop, the fluid had a slight brownish tint to it; but did not smell burnt.  The color and smell of the trans fluid are normal now; ie looks and smells just like out of container.

Drove 30 miles in-city yesterday, averaging 40mph with some cruising up to 50-55 for 1-5 miles.  No fluid loss detected.

The factory transmission cooler is not a supplemental cooler. If you are towing you need to install an auxiliary cooler. In addition it sounds like you need to change the fluid.

[Irish_Alley]

im with vile. the main cause of trans failure is heat. what it sounds like is youve heated the fluid and caused it to expand and come out the vent or the vent is clogged and it blew out a seal. if towing you need to "baby" the 700, it has a bad rep for being a weak trans but its not a bad one if its taken care of. i would add a cooler and change the fluid.