Blown freeze plug

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oldbutstillquic

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Cooling problems over the many years but never blew same freeze plug before. 71 340, minor modes-intake, cam, roller rockers, headers. Running with no problems 4 years. Blew side freeze plug. Replaced, then blew after 2-3 miles. Figured not properly set flush, installed another, same results. Top hose, engine hot, bottom hose warm. Found kink in heater hose. When ahead and repaced, water pump and thermostat. Same, 1st 2 miles 190, then spikes 230, then back 190 with top hose, engine hot. Flushed engine both ways. Ideas?
 
I had a 383 back in the day and had it wound up around 6500 rpm and it popped the plug out of the back of the right head, head gasket leaked and pressurized the cooling system.
 
check lower hose for sucking shut might be missing spring.
 
teringer said:
check lower hose for sucking shut might be missing spring.
Click to expand...

Look at this for sure. None of the newer hoses I've seen have the spring in them. Some parts places say you don't need them... I take it out of the old hose and put in the new ones.
 
There are places that sell oversized plugs as well, any issues with the port in the block?

It has been a decade or more since I bought a kit, but it included some oversized 'problem solvers' at the time.
 
I've done the same thing, swapping springs. Where can you get a spring now? Short of making one out of stainless spring steel.
 
Demonic said:
I've done the same thing, swapping springs. Where can you get a spring now? Short of making one out of stainless spring steel.
Click to expand...

Good question. I really don't know but some day we will run out of old ones! LOL
 
I have a hard time understanding incomplete sentences. Not making fun of you, but it's ME. I just recently found out I am dyslexic. Along with that, I sometimes see words that are not there and don't see some that are.

All that said, I reread your post several times and for the freeze plug, I would maybe go to a one size over size......OR you can switch over to a metric plug that's a tad larger. You can also drill the sides of the hole and pin the plug in. That's an old racer's trick. It works well.

As to the spike in temperature, what thermostat are you running? If you're running a factory 195, then I am calling that operation normal. Thermostat closed on startup, opens at the spike, then the engine cools after the thermostat opens. Just an internet guess.
 
brian6pac said:
I had a 383 back in the day and had it wound up around 6500 rpm and it popped the plug out of the back of the right head, head gasket leaked and pressurized the cooling system.
Click to expand...
Thanks!
brian6pac said:
I had a 383 back in the day and had it wound up around 6500 rpm and it popped the plug out of the back of the right head, head gasket leaked and pressurized the cooling system.
Click to expand...

Thanks!
teringer said:
check lower hose for sucking shut might be missing spring.
Click to expand...
 
Check the ribbed flex hose that are straight. I've seen them run the inner spring. I have removed those and used them in molded hose.
 
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