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  #1  
Old 07-08-2005, 06:00 AM
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Default freeze plug

Hi there

What's a freeze plug? Where is it located on my 258? Would opening that and cleaning some of that out help my colling problem (coolant boils over)?

I'm still working on other things like getting the radiator pressure tested (only get about an hour or two every few days to work on the jeep).

Thanks
Patrick
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Old 07-08-2005, 08:41 AM
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Default Re: freeze plug

Three freeze plugs, or more accurately core support plugs, are on the left side of the block. Removing them and cleaning out the water jacket isn't a good idea. They're not easy to get to, and can be a little tricky to install when access is limited.

First you should use a commercial flush solution and back flush the block. If done properly that will do a very good job, and it's relatively easy and inexpensive. But if you've changed the coolant beffore it turns muddy brown, it's probably not needed.
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Old 07-08-2005, 08:47 AM
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Default Re: freeze plug

Freeze Plug Definition:
An expansion plug located in the side of an engine block that is supposed to protect the block against freeze damage. Water expands when it turns to ice, and if the coolant doesn't have enough anti-freeze protection it can freeze and crack the block. The freeze plugs(there are several) are supposed to pop out under such conditions to relieve the pressure on the block. Freeze plugs can often be a source of troublesome leaks as a result of internal cooling system corrision. Ease of replacement depends on accessibility.
John
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Old 07-08-2005, 11:08 AM
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Default Re: freeze plug

In reference to JimLou's "3 core support plugs" (aka freeze plugs): Maybe the other 3 are called something else, but they are of the same configuration as the 3 that Jim cites, and I always treated them the same...

IMHO, I would NOT mess w/ the 'plugs' unless they are leaking, or the engine was on a stand (out of vehicle)... or at least the intake & exhaust manifolds have been removed.

In addition, I second his suggestion to use a good commercial flush to get out the 'gunk'. FWIW, I've realized very good results w/ the Prestone-brand flushes. Heck, just flushing the dern block, radiator and heater core w/ the garden hose brings out a tremendous amount of brown sediment & goo. Might also consider replacing heater hoses too - they can get pretty crusty on the inside.
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Old 07-08-2005, 07:06 PM
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Default Re: freeze plug

The core support plugs, AKA freeze plugs, are the three large ones. When the block is cast the sand cores that form the water jacket void are supported in the mold through the holes. After the iron solidifies the block is vibrated. That breaks up the sand which is dumped out through the core support holes. Then, to close them off, they are machined and steel plugs pressed in.

They get their common name from being pushed out when the block freezes, but if there were another way to support the cores, they wouldn't be there at all. They are a potential trouble spot and don't usually save the block anyway.

If the engineers were really concerned about protecting the block there would be five plugs, one between each pair of cylinders, and probably another five on the other side. That might do it.

The two smaller holes are threaded bosses where temperature sensors for the engine management system are screwed in. They are probably cast as solid bosses, then drilled and tapped.
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Old 07-08-2005, 07:14 PM
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Default Re: freeze plug

Like its been said, they are a PITA to replace when they are in the Jeep.

My rad and block were full of crud when I first installed the SBC.. I had very good luck with running the engine, opening a hole somewhere (temp, drain, anything) and then adding water in the top of the rad.. did that for about 7-10 min and it ran clear. Then I dumped it, added antifreeze, and then topped it off.
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Old 07-08-2005, 07:47 PM
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Default Re: freeze plug

freeze plugs = the devil
they seldom pop out to prevent block cracking.
what they do do is leak.
are a PITA to remove(most of the time you just push them into the block and install new ones. new ones also a PITA to put in sometimes.
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