i know that max is around 220F.....I am in the process of making some "given" adjustments. I have tested the thermostat in water and it opens at 180F which is 15F cooler than factory. I will replace the radiator hose that is leaking to rule out a $15 fault. I am changing the oil and putting in 10W30 as the ambient air temps are around 60F here. I have also verified the ignition is firing on time and correctly. I have a lot of new parts in this motor and I am trying to keep them cool while I verify that they are all working correctly. My main concern is that everything here has happened while idling and limited, controlled engine rev cycles. This is my first complete chevy rebuild and I have been very meticulous. I really just want this to end up a really dependable truck.