Strange 351C Crack Location?

[Fast1972]

Howdy folks,
Wondering if I could borrow your collective knowledge for a bit.

I've recently gotten a coolant drip from under my mustang (1972, 351C, 4 speed toploader) when it gets up to temperature, when coolant is pressurized.

Crawling under the car it looks like drips of coolant are appearing near the driver side coolant drain plug. It looks like it SHOULD be coming from the plug, but i have resealed/retaped it twice and still have the leak. And there seems to be about 1/8th in between the threads and where the water droplet starts.

Has anyone ever seen a cleveland crack from this plug? Or am I just not sealing this plug right?

 

[California 72]

The problem might be too much PTFE tape and I believe the allen screw should be flush as well.

Before I decided to machine the block, I removed all the original allen screw plugs to flush the motor thoroughly. While I did have one screw that needed to be drilled and re-threaded, when I did reseat them, I originally used the Blue Monster PTFE tape but didn't like the way it wrapped on the smaller plugs.

In my home projects, I opted the tape for the paste, especially because the smaller items never seemed to wrap well with my hands and arms succumbing to neuropathy issues and the botched, failed or avoided ulnar/carpal nerve repetitive movement surgeries. The paste actually applied very easily and it seems to be self-correcting when you get too much applied. The caveat would be, make sure it doesn't infiltrate the business end of the plug, just not comfortable with any excessive material floating around in the water/oil passages. I pictured it curing and clogging something critical down the line.

Anyhow, can't speak for how well it worked for me yet, since my motor remains at the machine shop awaiting work but, I'm happy with the success of it in all my handyman projects. Come to think of it, I won't know if it worked because the shop will probably remove what I had already completed when they tank the block.

 

[Hemikiller]

That plug is tapered pipe thread, and it looks like it was overtightened at some point, causing the crack. I'd try California 72's suggestion and use PTFE paste instead of the tape. Tighten only enough to seal the plug and see what happens.

 

[MikeGriese]

If that is a crack, isn't the plug the least of his worries now?

 

[Q1SVT]

… could also be caused do to freezing.

Should use a semi hardening sealant [type used when head bolts enter water passages]
JUST lightly insert plug, let the sealant do the work. So the plug does not apply force to open the crack more than needed to hold the plug.
Get some good coolant stop leak and add to engine that should stop the leak

Drive and enjoy her....

edited: use an iron plug or steel .... [your picture is not clear what type of plug you have...]

 

[Tnfastbk]

If it is a crack or to find out if it is a crack you need to remove the paint. If it is you might be able to use a dremel to clean it up and use some type of JB weld or something like that. Probably not a permanent fix but could buy you some time.

 

[Bentworker]

That is a bummer. I think I see a tiny black line radiating from the threads towards the drip. I think the “in frame” fixes would all involve leak seal and or epoxy.

If you pulled the engine it could likely be
brazed.


I’d drain and vaccum out the coolant system. Reseal the plug with less sealant and a lighter touch. Clean the heck out of the block surface (to bare cast iron). and encapsulate the whole mess in epoxy. (Maybe make a mold and hot glue it to the block). Use JB Weld or something more industrial like Belzona 1511.

With it being winter if you go epoxy make sure you follow instructions on ambient temperature.

 

[Sheriff41]

Many years ago (40+) I repaired a freeze crack in a 302 using JB Weld. It held up and the car is still on the road with its current owner.