Aluminum Block Freeze Plugs - Leaking

[Bunkie314]

I have had these damn plugs out numerous times to try and seal them. I have tried about every sealant that exists and still cannot get them to stop leaking. I even bought a tap, modified it, and chased the threads. I don't dare thread them tighter due to breaking the casting (2 TFFT rule of thumb and I am around 2-1/2) and wonder what the *%$$ to do next. After a few heat cycles they start to leak around the threads again. I am not sure where to go at this point. Its not big leaks, just weeping and I have to top off periodically.

Anyone else have this kind of issue with threaded freeze plugs in an aluminum block?

Should I just keep tightening them until they seal? The 2-1/2 turns is pretty damn tight.

Any recommended coolant system stop leak additive? I have been considering using Copper Coat.

I'm really frustrated with this as I cannot get a permanent seal. Sealant works (Caterpillar Form-A-Gasket has been the best and longest lasting so far) for a 100 miles or so.

[tcrist]

Will the white plumbers tape work?

[dynoroom]

Liquid teflon, it's a paste used in plumbing. Yuo can get it at the local hardware store or Summit or Jegs sell it branded by Fel-Pro or Edelbrock. Use it and never have a problem again.

[Tom Kirkham]

Have you tried Loctite? It has cured many leaking oil fittings for us.

Coolant stop leaks have been known to cause problems with radiators...

[flyboy1997]

I got that T Shirt also, mine was leaking on the engine stand from uh lets see GRAVITY! Pulled it cleaned threads & new O-Ring & it is holding a year later now that I have cranked it. Now the other side is leaking & this one is behing motor mount. Called Keith & he told me to add any stop leak made for aluminum, mine was pouring Big Time but after about 4 road trips so far with car SEEMS to be okay? Keith said alum. just shifts & cools uneven & stuff happens, says he always adds a stop leak to new builds. I used Bars Stop Leak & is working, heard good things on pellets also.

[olddog]

What type of metal are the plugs made from? Aluminum has a very high coefficient of thermal expansion. This means the diameter of the hole changes every time the engine heats up and cools down. If the metal in the plug is not aluminum (which is doubtful) then the plug is not expanding and contracting with the aluminum. The sealant is not going to take that abuse.

I will check some tables at work tomorrow, but I’m thinking brass may be fairly close to aluminum, but you have to be careful mixing dissimilar metals.

A plug with a flange and an O-ring would be best if the block is flat for the flange to mate up to.

Last thought, tighten it while the engine is hot.

[Rick Parker]

Are these tapered pipe threads or straight threads with an "O" ring like a port plug used with AN fittings?

Coolant will seak out a leak before distilled water will. I have 1 1/4" taperd pipe plugs exactly like Boss 302 in my smallblock. I noticed some very minor leaking shortly after the initial build. I put in a pellet that I obtained from a GM dealer and it sealed the leakage, no leakage at all in several years. Later I found it is common practice at the dealerships for the techs to throw one or two in the cooling system after major teardowns to eliminate any minor leakage and reduce come backs.

[Bunkie314]

First go around was Liquid TFE, coolant ran out like the plug wasn't installed. Tried about every brand of thread sealant I could find. To many to even list.

I even tried PTFE tape, which is the only thread sealant I was able to seal a 4500 psig air storage system. Still leaked after a few heat cycles.

I have also dropped down to a 7 psi cap to lower system pressure with some better results.

Block threads are an NPT with some kind of straight thread machined steel plug, I wish is was a STOR Port. Not sure Brass would be a good alternative due to galling issues, I assume that all the aluminum blocks are using these. 100 to 150 delta T shouldn't be that significant in 1-1/2 inches to hold 7 psi (I'd rather run a 15 lb cap though). Tightening when hot might overstress after cool down, so I have not done that either.

Flyboy,

I looked at the Bars Stop leak but considered the copper coat might be a better alternative. As Tom stated some stop leaks have issues stopping more than just leaks. Don't want to go there. Thanks for the info. Did he mention how many threads to engage after finger tight by chance?

I've also considered junking the plugs I have and going with a tappered or NPT plug. Straight thread to NPT should seal though.

Comments?

[Rick Parker]

Do these use a rubber "O" ring????

[Anthony]

I have used Indian head gasket shellack. Cheap and effective.

[Barry_R]

Have you tried using silicone? Cheap, easy, and flexible.

Moran Motorsports sells an o-ring plug conversion kit - not sure if they have the size you need.....

[olddog]

Aluminum expands 1.33 x 10^-5 in/in/F
Brass expands 1.11 x 10^-5 in/in/F
steel & iron expands 6.5 x 10^-6 in/in/F

Therefore using a 180 F temp range (32 to 212) and calculating a 1.5 inch hole, the aluminum hole will grow by 0.004 inch.

A brass plug will grow by 0.003 inch.
A iron plug will grow by 0.002 inch

The plug will deginately loosen when the engine heats up. Brass would cut that in half. Tightening it hot would help. I like the o-ring best.

My metal expert wasn't in, but I doubt brass and aluminum have any problems.

[olddog]

To my surprise, aluminum pipe plugs are readily available.

McMaster-Carr mcmaster.com has them. A bit pricey at $8.61 each.

Part number 44705K339 1.5" npt.

However aluminum parts, when oxidized, tend to become one part over time. If you try them, I would make certain that the threads are well sealed, with something that keeps them from touching.

I still like the O-ring seal best. I think Manowar said the same thing in another thread.

[Bunkie314]

Yes, Brass is available too. Unfortunately, two softies don't make a righty either. I'm going to use the ceramic sealant first before I do anything else. Several recommendations from others this has worked with the same problem.

Thanks for all the input guys.

[fostereast]

To seal brass plugs, my plumber uses a combination of teflon tape and putty. He says it usually works for his tougher sealing situations. I have no idea if it applies to your leak.

[RICK LAKE]

Old dog Try pipe sealer. It comes in a small blue apply bottle. Let cure for 24 hours. If you are going to use Alum plugs, use anti seize on the threads. This will allow you to remove the plugs down the road. It also acts as a sealer. GM sells sealant tabs. Come in a 6 pack. Try these, We use them on Caddie for the last 20 years. FOLLOW the instrutions. Let car sit over night then run. Go back to 15 psi cap. Rick L.

[vettestr]

I swear by Permatex, Aviation #3 sealant for freeze plugs and bolts or studs that go into water/coolant. Use Aluminum plugs so the expansion rate is the same would be helpful. You mentioned you have chased the threads already in the block but how about checking the threads and pitch on the plugs. Determine the bore size and thread interference using a plug with blu-Inga or dye.
There is a ceramic coating in liquid form that works well to seal a block around liners, plugs, etc.. Another idea is to clean the block and plug with a chemical used to clean aluminum before welding, it is a liquid that will foam a bit as it etches and cleans the surface from earlier attempts to seal. Good Luck - you will get her to seal up. Keep the faith