In winter my 4L80E trans oil never sees 100 deg unless it gets over 40 deg. ambient. I installed a oversize cooler. Now I wonder if I should also use a thermostat. 4L80s do heat as soon as the TCC unlocks. I wasn't aware of the OD sprag heat issue.
1951 3800 1-ton "Earning its keep from the get-go" In the DITY Gallery 1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.
