427 boils over

A friend has a 427 high tower bored 60 over with in two to three min It boils over .He has pulled the heads put in new gaskets .We checked the timing .We have run out of things to check that we know of .  

take a look that the thermostat is installed correctly....  the last time i saw a car overheat that fast ..  the stat was installed backward...      take it out.. put the housing back on.. refill the cooling system... fire up the motor ... see if the coolant circulates at speed...  if so,...  replace the thermostat...  

there are a few engines with directional head gaskets...     most engines the water comes out the pump... into the cylinder block...  around the cylinders and up through the back of the heads... forward through the heads to the front of the intake manifold...


there are also reverse rotational water pumps... designed for being driven backwards by the back of a serpentine belt..


let the engine cool....

take the water pump belt off..     fill the cooling system to block the opening of the radiator... start the motor... if there is instant movement..  with the coolant pouring out...  you still have a problem with a crack... in the block or head... or still a sealing problem with the head gasket...

when you took it apart...  did you find one or more pistons.. that were totally clean on top when others had carbon on them????/

if you have access to compressed air... and a compression tester with the proper quick connect to hook the hose to the shop air line...     take out one spark plug at a time...     with the fan belt off... and the trans in park or neutral...  bump the motor over with a remote starter till you get that cylinder to exact top dead center..  take the core out of the end of the compression tester hose.. don't loose it..   then pump compressed air into the individual cylinders one at a time bringing each one to tdc compression...  watch the coolant level...  if it rises... you have found the leaking cylinder...

warning..  the engine can rotate fast when you turn on the air...    really fast...  fast enough to catch your arms or clothing in the belts or pulleys...  so be careful....  

Hey thanks for the reply .My friend has done everything you wrote here last weekend
We work at a auto repair .This has all of us beating our head against the wall .  

just one more thing...

does the radiator cap hold pressure...???????/

i have run into several radiator caps that the dime sized disc in the middle of the rubber seal is not spring loaded towards the seal... it just flops loose... needing a direct splash to close and seal...

if they tested everything...  what were the results..???????

we are talking about a big block chevy right...  

is there any chance that somebody spread RTV all over the head gaskets.??? and the RTV plugged up the holes..

i have had wonderful luck sealing head gaskets with Hylomar...  harbor freight has it cheep... look up sealers ...


did the coolant circulate????     i take it that you have a infra red temp gun... can you check for cold spots on the radiator..

what happened when you pulled the thermostat...   did the coolant circulate at high speed?????    when you revved up the motor... did it try to flatten the lower hose????   that would indicate a clogged radiator..

is there any chance that something is plugged someware.????  a capplug over the waterpump opening with the hose pushed over it...  a shop rag shoved into a upper or lower hose...    tape over the water pump mounting holes...    missing or loose impeller in the water pump...


overheating in 3 minutes is way fast...

does it build pressure in 30 seconds????? if so.. leaking gasket or crack somewhere...

something is blocked... if all else fails.. pull the water pump and the thermostat... stick the garden hose in each side of the waterpump mounts in the block... see how easy it flows out the thermostat opening...


how about more of a hint of what motor you are working on????    some head and block casting numbers...  

the last motor I seen that heated up that fast had a blown head. check the exhaust ports for cracks. never no.

there is a kit you can get from the tool man that test for carbon in the cooling system. this will tell you if the heads or head gaskets are blown or have a cracked block. If the test comes up clean then it rules them out. I always got mine from the matco man.

best of luck  

Yep, check for cracks in the heads.

Also, the bottom row of water jacket passages, are the ones in the middle drilled? Recently helped a friend with a 402 having hte same problem, block didn't have those holes drilled, after drilling them out, no more overheating problems.  

I have seen a similar problem on a big block and it had a couple of bad exhaust guides and this allowed the cylinder pressure to force the coolant out soon after it was started. I dont think the engine is overheating that quick. we had the heads worked but the guy didnt pressure test them, and we had to take them to another shop and get them repaired.