Can a kinked trans cooler line cause engine overheating?
Im gonna dissent on running without a stat. I think the controlled flow rate the stat provides through the radiator is important to the efficiency of the system. You need the motor to get to operating temperature ASAP to reduce cylinder wear and for general driveablilty. An open stat is plenty of flow to cool a stock 318 motor with a functional radiator and water pump (impellers can rust off old pumps). Water in the block can only get so hot as it is a closed system up to the blow off pressure of the cap. Id feel the rad in all 4 corners to make sure its getting flow through it, could be a plugged rad. A lean carb will elevate temps too. Id lean toward the RTV propping the stat open before keeping it closed.