- 3 mins run time is not enough to reliably get up to temp
- the temp sender is the ground, hopefully you haven't used any paste sealer or teflon tape on the threads
- the sender location on a 283 stat housing should work fine, assuming you don't have an air lock
- the stock rad should cool a 350, providing it can stand the pressure [at least a 7# cap]
- without running the engine under load long enough for it to attain a stable operating temperature, AND then letting it sit at idle for a period [as in traffic at a stop light] you never will know if it's going to overheat
Bill
