most electric fans do not move enough air for towing.
This may be your problem. The best 16" electric fan on the market is sourced to NASCAR and pushes 3200CFM at 0" of restriction. At the typical 1.4" of restriction you find in a radiator core, it is down to 2200 - 2300CFM. The best commercially available fans (Spal or Tri-Pac) flow 2900CFM at 0" and drop to about 2000CFM at 1.4"
If you have a hayden or other 16" fan from your local FLAPS, you are pushing about 1500CFM thru the radiator which is about half of the airflow you need.
Scott
