i run a 388 sbc also with the block filled to the bottom of the water pump inlet i run a meziere eletric pump and no t stat, i cant get my motor to run above 160 i use my motor alot on the street and its 15.5:1 compression. if i do let the temp run up 180-90 not using the fan, it does take longer to get the temp down back around 160. most of the time i usualy dont use the fan she just runs 160 cruising around. hope this helps your decision.