Why should I replace my freeze plugs?

nitequill · Jan 8, 2007

Is it necessary to replace the freeze plugs? What are they used for?

Eyeless_Seven · Jan 8, 2007

Freeze plugs (also called "blind" or "expansion core" plugs) are small steel plugs used to seal the holes in the engine block and head made in casting. They expand and flatten as they are driven into place, and make a tight seal. These are designed to hold the pressure of the cooling system, but to pop out if the coolant in the block ever freezes. If the one's you currently have, are not made out of brass, I would replace them as they will rust out and become a problem in the summer time.

D.Hearne · Jan 8, 2007

If they're not leaking, leave them be. They're a bitch to change, no need inviting more work than you need. Easiest way to replace them is when the engine's out of the car.

69 Rustang · Jan 8, 2007

You don't say whether the engine is out or not. If the engine is out--no question about it just change them as it is easy and they are cheap. Changing them "in the car" if they start leaking or rusted out is brutal--I did it once and should have just pulled the engine.

mustangmike6996 · Jan 8, 2007

core plugs not freeze plugs

the common term freeze plugs are not what most people think they are for... if you are going to have an extreme system pressure build up it will blow a radiator hose or something else.. these plugs are used during the casting process to remove any excess sand that was use in the process. each engine is cast in a one time use hard packed sand. the plugs are then driven in place to cover the hole. high performance blocks offer threaded core plug holes for a threaded pipe fitting to be installed as well.

Max Power · Jan 8, 2007

mustangmike6996 said:
the common term freeze plugs are not what most people think they are for... if you are going to have an extreme system pressure build up it will blow a radiator hose or something else.. these plugs are used during the casting process to remove any excess sand that was use in the process. each engine is cast in a one time use hard packed sand. the plugs are then driven in place to cover the hole. high performance blocks offer threaded core plug holes for a threaded pipe fitting to be installed as well.

Correct. I have seen blocks freeze and crack before any plugs come out.

65ShelbyClone · Jan 8, 2007

Max Power said:
Correct. I have seen blocks freeze and crack before any plugs come out.

It seems to be pot luck as to whether the plugs or the block is what pops. I find it cheaper and easier to make sure I have enough antifreeze to prevent either. Enough AF will keep the steel plugs from rotting for a long time.

Besides that, if the engine is out, replace them with brass. If the engine is still in the car and nothing leaks, don't worry about it.

xoxbxfx · Jan 8, 2007

Max Power said:
Correct. I have seen blocks freeze and crack before any plugs come out.

call me lucky..my freeze plug popped

69gmachine · Jan 9, 2007

xoxbxfx said:
call me lucky..my freeze plug popped

OK, Lucky xox. The point here is that they are not designed to pop out with freezing coolant, even though they often do, which led to the misnomer of "freeze" plugs in the first place. I too have been lucky with one block. All 3 plugs on one side popped out. None did on the other side. Unfortunately I was not so lucky with the heads. One of them did crack. I was running straight water in the summer while I was testing the engine. The car wasn't ready to drive so it sat until winter. By then I had forgotten I had put water in it.

If/when you have the engine out, replace them, otherwise do as D recommended and leave them alone if they don't leak. Just my .02.

ForceFed70 · Jan 9, 2007

To say they arn't designed to pop out is silly.

Clearly by looking at the design, that's what they are supposed to do. Otherwise, why would ford use this particular design to plug casting holes? There are much better ways that are less prone to problems. They are definately used to block holes from the casting process, but blocking the casting hole is not their only purpose.

As for popping the radiator hose instead..remember these are freeze plugs here. Coolant does not flow well when frozen. And remember an engine will freeze from the outside in. Meaning water passages exiting the block will be the 1st to freeze and will in effect "plug" the block. Not allowing pressure to escape.

nitequill · Jan 9, 2007

great point

nitequill · Jan 9, 2007

being that my engine is outside the car right now, i will go ahead and change the plugs... but how do i take that damn things out? and do they go in just by hitting them with a hammer?

Eyeless_Seven · Jan 9, 2007

I use an old socket and a hammer, and needle nose vise grip's will usually work to get them out. Make sure you get them out of the block as they will rust away and plug up the radiator or cause problem's with the water flow.
The size is usually stamped on them , you will need that to replace them as "some" auto counter people will give you the wrong size.

ponyX2 · Jan 10, 2007

When you change them, clean the hole with a little sand paper or wire brush and put a thin film of gasket sealer around the edge before you drive em home.

BornInAFord · Jan 10, 2007

Usually a sharp rap with a hammer against a wide screwdriver on one side of the freeze plug will push in that side, allowing the freeze plug to rotate partly in, partly out, but not fall into the block. It is easy to pull the plug out at that point. It is a pain to get a plug out if it is inside the coolant passages in the block. Another way is to drill a small hole in one and use a screw and bodyshop slide hammer (or just screw the slide hammer into the plug) to pop the plug out. You'll replace the plug anyway...

Daniel

mustangmike6996 · Jan 12, 2007

i am not saying that they do not pop out but they are not designed for that feature. added benefit yes. as for the design its cheap to install a stamped steel peice of metal instead of a threaded hole and plug.

D.Hearne · Jan 12, 2007

mustangmike6996 said:
i am not saying that they do not pop out but they are not designed for that feature. added benefit yes. as for the design its cheap to install a stamped steel peice of metal instead of a threaded hole and plug.

Correct. The only reason the Boss 302 and the 427's got threaded core plugs was to prevent their popping out in long races such as Lemans, Trans-Am and Nascar. To thread all production blocks would have been nice for us, but cost prohibitive for Ford.

Why should I replace my freeze plugs?

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