Just blew out a freeze plug doing a burn out. Why do they have a freeze plug?

 

I think you'll find all heads have a core plug so they can get the casting sand from out of the inside. The "freeze" plug name is rather misleading as the intent of its use has nothing to do with freezing.

 

How do I prevent it from blowing out again?

 

The best way is to machine threads into the hole and use a threaded plug. The only question that I have is why is there so much pressure that caused the plug to blow in the first place? Radiator pressure should never be enough, do you possibly have head gasket issues?

 

Not sure. I did put on a new weiand intake manifold that doesn't have the water port crossover on the rear. The heads do have a water port.

 

Maybe the previous owner didn't install them correctly. The motor was missing 5 oil plugs, incorrect pushrods for roller rockers and guide plates,

 

Those were my first thoughts, too! Although on the tap-and-plug, I have to wonder if that's wise with aluminum heads/steel plugs? Brass maybe? I would assume ProComp installs the plugs at the factory.

Was the engine fully warmed up (thermostat open) when you did this burnout?

 

The heads are made to mount to either bank of the engine so they must have a water port at each end. The manifold only needs the water crossover at the front where the water outlet is located. On my 351W with an Edelbrock 2181 manifold, there is no rear crossover either. I too am running ProComp heads. There may also be an issue with corrosion between the plug and the aluminum head. I am running Evans waterless coolant for just such a reason.


Here is a pic of my engine with the Edelbrock 2181 and the ProComp heads:

 

CharlieLed, are you using brass plugs?


I am having a difficult time finding plugs to fit these heads. i measure 1.15 in diameter. maybe 1 3/16 brass plugs might fit???

 

I have never given these plugs a second thought...before today I had never heard of anyone having an issue with them. The ones in my heads are the ones that came with the heads. Given that measurement and understanding that these heads are cast off-shore, I think that a 30mm plug should fit... Nissan Factory OEM Freeze Plugs 30MM Pack Of 5 - 00933-1301A

 

First off you can stake them like you do to the oil galley plugs to help retain them. Next there does not appear to be any sealant on that plug hole, sealant helps retain them.

As to what Wayne said I believe he may be slightly right, I was told by several old ( and I mean long dead old) mechanics that they are freeze plugs because as the water freezes and expands the plug is supposed to be pushed out thereby avoiding cracking the block or head. They are also used for the casting process.

 

Should get two plugs tomorrow at 10am. I'll report back. I like the "staking" idea. I did that to my oil plugs behind timing cover

 

They are called core plugs in the UK but have the dual use you describe - An intentional weak point in the event of freezing or overheating as well as a remnant from the casting process. If you clean up the hole and use sealer you shouldn't have a problem. Because if you do a new plug is easier to deal with than a new head,

 

My father had a 71 Ford Torino with a 302 that froze one winter. The "freeze" plugs never budged. But the heads and block both had chunks of cast iron blown out in quite a few places.

I never believed the "freeze" plug thing since. A little OT but, I felt it may clear things up on casting or core plugs.

 

Once corrosion sets in they might as well be welded! Certainly not an alternative to putting in anti-freeze!
If the casting does crack with frost and you have very rare engine there is an amazing process called cold stitching that can save it from scrap. Not many people around who can do it though.