Newly built engine is leaking coolant and I'm stumped

[Sheriff41]

I think the Rickster has a spirit of its own and is just helping you find problems on the car so you get them sorted out sooner rather than later.

 

[73MustangCoupe]

This morning I was able to was able to drain the cooling system, removed the alternator, and got a lifting sling on the motor. I picked it up enough to remove the motor mount, pressurized the cooling system, and hit it with the black light. A steady stream of coolant ran from the freeze plug to the oil ban rail, and to the back of the engine. So a leaking freeze plug is the cause. I've got a replacement freeze plug ready for pick up in the morning, and once that is installed, I should be back in business.

 

[Kilgon]

This morning I was able to was able to drain the cooling system, removed the alternator, and got a lifting sling on the motor. I picked it up enough to remove the motor mount, pressurized the cooling system, and hit it with the black light. A steady stream of coolant ran from the freeze plug to the oil ban rail, and to the back of the engine. So a leaking freeze plug is the cause. I've got a replacement freeze plug ready for pick up in the morning, and once that is installed, I should be back in business.

I don't think I need to really say this but I would make sure there are no other leaks after you replace that freeze plug before setting the engine back down. Hope all goes well for you.

 

[will e]

Really happy for you. PITA for sure but could have been so much worse.

 

[73MustangCoupe]

Thanks, guys. Today, I picked up the freeze plug from AutoZone. I wasn't happy with it. It was so thin, and more like a washer than a shallow cup. I also found that another freeze plug had a trail of flourescence leading from it. So it's two leaking freeze plugs. I've got a complete set of Milodon freeze plugs on order from Summit Racing. They should be here Wednesday, and once installed, I'll pressure test it before I stab it back in the engine bay.

In the meantime, I've got wiring I can play with.

 

[timachone]

Go for the brass plugs, not the simply metal ones. The brass ones are thicker and holding up longer, in my personal opinion...

 

[cjstaci]

I always use permatex #1 on soft plugs.

 

[73MustangCoupe]

The Dorman freeze plugs at AutoZone are very thin, with narrow flanges. The Milodon freeze plugs that I have on order are brass and about twice as thick as the Dorman freeze plugs. The flange is 2-3 times wider as well. I will clean the opening with sandpaper and use some RTV sealant around the edges when I put them in.

 

[Sheriff41]

The deeper freeze plugs are a little easier to install than the thin ones but both work well. Brass doesn't corrode like the steel ones but if you maintain your coolant/antifreeze then you shouldn't have any issues with either. Paint the exposed side of steel plugs. In 40+ years working on engines I've never used sealer on freeze plugs and never had a leaker--maybe I've been lucky. Make sure the surfaces are clean and smooth, and drive the plug in as straight as possible.

 

[73MustangCoupe]

Well, I removed the passenger side headers and used the engine hoist to lift that side of the motor enough to remove the motor mount. Sure enough, there is a nice little trail of fluorescence from the bottom of the freeze plug to the oil pan rail. I could see a good way to replace it in the car, so I pulled the motor, and once on the engine stand, found that a freeze plug on the driver side was also leaking. A third freeze plug was suspect, so I decided to replace all of them. I used a thin film of Permatex UltraBlack sealant around the perimeter of the freeze plug to make sure there were no microscopic voids that might want to leak.

After I finished, I let it sit overnight, and the next morning, I dropped it back into the engine bay and hooked up the radiator and heater hoses. I ran to O'Reilly's Auto Parts and got the radiator pressure tester, and pumped it up to 13 PSI and waited to see what it would do. After 3 hrs, it was still holding 13 PSI, and after 24 hrs it had only lost 2 PSI. I think it's fixed. Now, I just need to get the rest of the drivetrain back in it, and get back to getting the Rickster done.

 

[mrgmhale]

Go for the brass plugs, not the simply metal ones. The brass ones are thicker and holding up longer, in my personal opinion...

Agreed. I had an instructor for an engine rebuild class who beat that into our brains at every opportunity. He would tell us it is not worth the little lower price to go with the less costly core )freeze) plug. Brass and only brass, and I have been an advocate of that ever since. I have never had a problem driving in a brass core plug, nor having one leak.. Using Permatex to help ensure a good seal may be overkill, but better than than a mystery leak.

I am glad you found the cause of the leaks, hope the new core plugs do the trick, and am also hoping you encounter no more little surprises like that. Imagine how you would have felt if you were doing that job "on the clock" as your primary source of income, and you had to do all work over for free... Little things like that can become a nightmare really fast.