ReallyWildStuff

I have my 455 on a test stand and had run it good and well up to temperature not so long ago (over the summer) with no coolant leaks...I then drained it of fluids so as to fix various things (oil plug leak, custom stainless water neck studs for electronic cruise, leaking trans pan - but _not_ leaking freeze plugs though).

Last thing I did (August) was clock that mini starter to fit - and it wasn't leaking coolant then either.

But SINCE then, "seemingly just sitting there" (without coolant in the radiator and only residual coolant in the engine) the freeze plug in the head directly above the starter has leaked quite the little bit of coolant out of it.

The freeze plug installation is probably 15 years old. Absent banging on one of them with a punch and hammer (or similar), or running the engine through some sort of calamitous temperature event (which didn't happen), or a rust-through of the plug - what would cause a freeze plug to just start pissing coolant for "no reason" (and while not pressurized)?

Is there a superior replacement freeze plug part available, or is one freeze plug just like any other?

What sealant should be used between the head casting and the plug?

Although only one freeze plug (in only one head) has "sprung a leak" I guess I should replace all the head plugs...yes? Should I plan to replace block plugs too (also 15 years old)?

Thanks

joe_padavano

Yeah. Brass freeze plugs don't rust.

ReallyWildStuff

Very fine. The ones in the heads now are indeed steel.

There must have been some reason (like "availability") I ended up with steel instead of brass ones.

Do you have the spec handy, or a part number for all the correctly sized head expansion plugs packaged together?

ReallyWildStuff

https://www.summitracing.com/parts/mil-34045



This picture of the Milodon retail card shows six brass BLOCK plugs - and not the HEAD plugs I need. Isn't that correct?

joe_padavano

Usually it's cost. OEM is steel.

Size is 1.25" diameter, .4375 deep.
Pioneer part # EPC18B
Melling part # MPC18B

Fun71

The last couple times I bought brass freeze plugs I got them at the local NAPA store.

Run to Rund

I use steel, thinking they are mechanically stronger, with a coating of ultra black RTV on them and on the holes in the block/head. Even better would be NPT plugs if you want to tap the holes. It is hard to get the tap started in the block holes, and the head has bosses in the way internally so you have to cut off the end of the tap.

joe_padavano

They have to withstand all of 16 psi. PVC would be strong enough.

Tedd Thompson

Most if not all marine engines come with brass freeze plugs as a rule. There shouldn't be a shortage at any parts house..... Tedd

VC455

Mr. Wild.

You wondered why the plugs decided to leak after the block came back from vacation.

Antifreeze absorbs carbon dioxide from the air and becomes acidic. There are additives that delay the onset of acidity but they get used up (that's why you have to change anti-freeze periodically).

Anti-freeze in the cooling system has is little air contact, but when you drained the block the anti-freeze then had a large surface to absorb carbon dioxide. The antifreeze became acidic and corroded the block or the plug or both, causing the leak.

In the future, don't leave a residue of anti-freeze in anything that will be stored. Rinse it out with water. It the part is cast iron, do a final rinse with water having a tablespoon of baking soda in it, drain what you can, and allow the rest to evaporate.

ReallyWildStuff

Thank you all very kindly. I hope I don't find too big a mess inside the head coolant passage when I swap these out.

I suppose I will go with "BRASS" replacements for the leaking steel expansion plugs in these C Heads.

Qty: 4 (2 on each head), is that correct?

Shall I use the aforementioned BLACK RTV when I install these copper plugs? Something else instead?

Thanks again -

BrianA

joe_padavano

Brass, actually

Yes

I've really not used anything - just hammered them in.

ReallyWildStuff

I'm going to pick up five examples @ NAPA tonight. $1.99/ea.

Is the best way to remove the old ones still to puncture them in their middles and pry them out from the inside?