ok i put a used 400 in my 77 f 150... it runs great , but once it gets warm it starts making a weird "boiling" noise ... like a popping sound of the water surging or something... it does this even without the thermostat in ! tried different water pumps but still does the same thing. please help! could it be a cracked block? compression test and coolant pressure test say everythings fine. thanks for any suggestions

 

sounds like the classic symptom of a head gasket or two installed backwards. some gaskets you can see a small bit of a tab sticking out the front of the head to indicate that the gasket is on correctly, if you have the tab in back stop everything.

i've also heard of scale coming loose in a stored engine and blocking the same passage that is different in the head gasket, exact same symptoms but the tab is definately correctly facing front. that guy pulled his hair out until he finally pulled the heads and found the scale blocking the passage.

you are sure the radiator flows? you might want to get it checked out before you pull the heads? there's no telling without looking what could be blocking a passage in a used engine that you don't know the history of. how long was it sitting and where? how many goofs had access to it? were the holes all plugged when it was shown to you the first time? i've seen a rat's nest in a cylinder of a "known good engine" because it sat with the plugs out of it. the poor guy who's truck it was going into was going to just stuff it but i finally convinced him to pull the heads and inspect. that would've been the third engine that died upon fire-up in that truck in a week.

 

Without a thermostat the coolant will bypass the radiator and circulate inside the block. You need to install the proper 195° stat.