Quote Originally Posted by 780ripper View Post
Hi Guys, I'm changing to a cooler (160°f) thermostat and would like to know what temperature range to set my cooling fans to?
I figured that a good range would be 170°F on and 155°F off, with about 45sec run on time after the ignition is turned off. Any input is appreciated.
Those fan-on settings are too cold for any thermostat, even the 160°F thermostat. Once a thermostat opens it should not open and close chronically; it should open wide and stay wide open til the powertrain is done working.
Quote Originally Posted by 780ripper View Post
several reasons for the thermostat change:

the engine oil, transmission oil and coolant are tied into the same radiator so everything then runs hot
im running a cast iron big block which generates a ton of heat, this degrades the oil and kills bearings
any oil i put in looks vaporized when i change it, and
i plan on towing my trailer with this truck so i want to try and run it as cool as possible.
160°F thermostats are fully closed below 160°F, and fully open by about 176°F.
If you want the fans CONSTANTLY on for some strange reason? Fan-OFF @ 160°F or less.

With a 160°F / 71°C thermostat:
Set the Fan-OFF @ 176°F / 80°C. Any lower and the thermostat will stutter.
Set the Fan-ON @ 185°F / 85°C. This might let the fans shut off while the vehicle is moving fast enough to do the fan's work for them (45MpH or more).

Be sure the radiator (and external ATF cooler if also equipped?) are getting as much airflow into them as possible so that the fans' work is made easier.
Check your baffling, and consider adding coroplast in choice spots if need be.