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Look for a leak at bypass hose nipple where it attaches to the thermostat housing. A leak there works its way to the rear of the engine. Happened to me, drove me nutz!

"FREE SAMPLE"

Total agreement on using sealer on the frost plugs when installing them.  Another spot to look at for coolant leaks is at the turtles used to tighten the intake manifold down around the heat riser passages.  The threads for the turtle studs in some of those heads do break into the coolant passages and if not using sealer of some sort on those particular threads, there will be a seep coming from there.  That small trail of leaking coolant finds its way to the back of the engine and is very easily mistaken for a head gasket or rear frost plug leak.  Those intake manifold studs give you another area to check out.

Lorena, Texas (South of Waco)

I am chasing a nightmare. My machine shop installed the freeze plugs in my heads they had machined This engine lives in my 1955 C600 COE. The left head has had this mysterious drip of coolant from the corner of the head right onto the spark plug wire loom block that mounts right at that corner...I thought there was something right there at the edge of the head and the block allowing that every 12 second drip to happen right there just a quarter inch to the left of the last short head bolt there in the corner....Someone suggested that I sprinkle baby powder to see if the leak started upstream somewhere else....it is really hard to see in that area . The dog house is removed but part of the firewall and the floor where part of #7 and all of #8 cylinder sit under that piece of the floor... mine are brass...make sure you have that  ENGINE mating surface for the freeze plug VERY CLEAN. Make sure you use a soft sealant like Permatex Aviation. I SEE NO SIGN the machine shop put any sealer on. I went to ask  the machine shop about all of that  "We do many many many of these and we put only a very little sealant on at the cup end of the plug so you cant see it....I know That goopy sealant stuff is IMPOSSIBLE to put on without seeing some trace of it....not even a spot of it is present on my 4 head plugs they did. It turns out the back one leaks at position 7:45 and the front one on that  same left head has a drop sitting right there....USE THE CORRECT TOOL ALSO>>.a socket is not the right tool a freeze plug needs to be put in ONLY with the edge of the plug making contact with the tool ....hitting anywhere in the center of the freeze plug will distort it and have it leak....if anything a steel one is better because it wont distort as easily on install. 

Gary Z. "ETTT=Ethyl*THE*Tool Truck" 1955 C600 272cid Y block T98 Eaton 1350 / "Brutus" 1972 F250 360cid FE C6 Camper Special Cust Sport/ "Edith" 1955 C600 restomod on a 2002 E550 Chassis 7.3 Powerstroke EOD/"Panzer" 1976 MBZ 450SL

Howdy,

If I had a choice and the engine was out it would be stainless steel and brass in that order.
Now I am partial to those because I have actually had regular steel corrode badly enough to "pop" out on their own!
Aside from the fact you have to SERIOUSLY neglect your cooling system to get that to happen, SS and brass are a little softer and might stay in "better"!

Also understand that they are NOT "Freeze" plugs.    They're CORE plugs necessary to plug the holes required in the casting process.  They're not there to "prevent" freeze damage. 

They ARE a great freeze damage detector in that if they do get pushed out because you either didn't put enough AF for the temp encountered or had regular water in the block (I.E.  your boat has that REALLY COOL 312 marine engine installed) , the block will more than likely be cracked either internally or externally if you didn't bother to drain it  prior to the the winter freeze!



There's nothing cooler than a vintage inboard with a Y-block inside!!

Cheers,

Rick




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1955 F-600/272/E4OD// Disclaimer: No animals were injured while test driving my F-600 except the ones I ran over intentionally!

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Put a little gasket sealer around the holes when you put them in.

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

The engine is out of the car ,naked block on a stand no trouble to access any opening

good luck around the starter core plug

Found some stainless steel freeze out plugs I will be using . Thanks for the options

I’d forgotten about those expanding rubber plugs. I used one years ago, worked fine. It was still in the car when I sold it.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ