Core/Freeze Plug blow out

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MikeG69

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I replaced a couple of leaking block plugs on my '77 360. Used the 1 5/8", Doorman 555-030. It shows the open end dia to be 1.643 with the closed end diameter, 1.63. Heigh is 0.50 This plug dropped in with not a lot left to drive it in. I tapped it in with the rim being a bit more than flush, gauging it on the others that were installed when engine was rebuilt. I bought the engine already built. Ran it up to operation temp and drove it with no problems. Stopped, let it cool down, and took it for another run. Dropped the hammer and blew the plug out.

Has anyone else run into this problem? Does the plug need to be driven deeper into the block? I see that Doorman makes a 555.068 in a 1 41/64. 1.647 on the open end and 1.635 on the closed end. It is a more shallow plug at 0.360. Ideas?
 
I'm reading the a neutral pH is desirable.
(7)
I'm also reading that a base pH is desirable.
Confusion reigns.

And how reliable is the voltmeter test?
(Less than .04 volts from fluid to ground).
 
The top edge of the cup plug should be just below the chamfer on the freeze plug hole and square - not crooked...
 
adriver said:
I'm reading the a neutral pH is desirable.
(7)
I'm also reading that a base pH is desirable.
Confusion reigns.

And how reliable is the voltmeter test?
(Less than .04 volts from fluid to ground).
Click to expand...
FWIW.... Base pH is where you end up with fresh antifreeze and it's additives. The tendency is for the coolant to move towards acidic as things gradually corrode so you want to start out on the alkaline side for pH.

Dunno on the voltmeter test... can I cheat and look on the internet, and pretend I knew? LOL
 
OP, so the plugs blew out when you got on it? By any chance, do you have some mild, persistent overheating? If so, there may be a combustion chamber leak into the cooling system, like a head gasket leak, or head crack. Just a thought.....

Your research on the slightly large plug sounds like a good idea. The fact that the first plugs dropped most of the way in is a sign that they were too small. They typically fight you all the way in. You should use a thin coat of #1 Permatex or similar on the edges.
 
Thank you for the responses.

I made sure the surface was clean and dry. No pits or rust issues.

No socket used on the install. I bought a plug installer tool and am driving them in by the edge. I am using Permatex 2 on the edges of the plug.

Yep. Plug popped out when I got on it. No overheating issues. I am going to pick up a couple of the larger plugs and see if they fit better.
 
OK, if another pops out, then you might want to borrow a cooling system pressure tester, install it, heat things up, and look for pulsations on the gauge when idling, all warmed up. That'll show up any significant combustion leakage.

The other source of added pressure when you rev it up is just the increase in pressure of several psi in the block and heads when the water pump revs up, and creates back pressure against the (intentional) outlet flow restriction of the t'stat. Your blow-out might just have been that simple.

BTW, Permatex #2 is more gooey and will not quickly dry up like a glue and seal like Permatex #1. #1 is more made for things like metal-to-metal sealing that is not meant to have any flexibility and is very permanent (unlike a gasket). (It is used, for example, in sealing together the 2 halves of the crankcase of small aircraft engines.)
 
Thank you for the advice. I picked up the larger plugs today, I'll grab some Permatex 1 and give it another go.
 
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