Rear block core plug

[Landon427]

So I had my '99 2.5L rebuilt by a local machine shop. Got it back, assembled it, put it in, filled with antifreeze and noticed a drip at the back of the motor. The core (freeze / expansion) plug on the back of the head was dry, and the head gasket was dry. Borescope showed it was the core plug on the back of the block that was leaking.

I pulled the trans/TC and clutch and the machine shop came and replaced it, but with a different 'style' of plug. They say they always use a thin film of Permatex aviation form a gasket on the bore hole and have never had one leak before. Does anyone know if it is a bad idea to keep the new one they used (the old one they installed that leaked is the thicker one on the right, new one is now in the motor is on the left)? They measure about the same in diameter, I'm just trying to avoid more problems. Thanks for any input.

 

[Rickyd]

It leaked without any heat cycles? I hope they used something with more of an interference fit

 

[Landon427]

They switched brands; the 2nd one was a Pioneer brand core plug. I don't know what brand the first one was. I waited a full week, then added coolant. It didn't leak, so I pressure tested it for about 20 minutes at 10-15 psi (small leak in pressure tester hose; radiator cap is stamped 16 psi). No leak at the core plug, so I installed the transmission and broke in the engine (25 minutes varying rpm from 1500-3000). Noticed a small leak... It is leaking again. I'm at my wits end (what few of them I have). The leak is fastest during heat soak just after shutting off engine (1 drip every 6 seconds) and when it is cold it doesn't leak at all. I think I'm going to try a GM leak stop tab.

Question: If you were in my shoes, what would you do? I mean specifically, what is the very best method you know of that is dead reliable when replacing core plugs? The transmission re-install was a fight but if I knew I would solve the problem, I would pull the transmission again and replace the plug.

 

[Landon427]

They switched brands; the 2nd one was a Pioneer brand core plug. I don't know what brand the first one was. I waited a full week, then added coolant. It didn't leak, so I pressure tested it for about 20 minutes at 10-15 psi (small leak in pressure tester hose; radiator cap is stamped 16 psi). No leak at the core plug, so I installed the transmission and broke in the engine (25 minutes varying rpm from 1500-3000). Noticed a small leak... It is leaking again. I'm at my wits end (what few of them I have). The leak is fastest during heat soak just after shutting off engine (1 drip every 6 seconds) and when it is cold it doesn't leak at all. I think I'm going to try a GM leak stop tab.

Question: If you were in my shoes, what would you do? I mean specifically, what is the very best method you know of that is dead reliable when replacing core plugs? The transmission re-install was a fight but if I knew I would solve the problem, I would pull the transmission again and replace the plug.

Following up with what finally worked. The third replacement plug was a Melling brass plug; the machine shop owner installed the plug; they cleaned the bore well with brake cleaner; they used Loctite 518 as sealant; they seated the plug a little deeper (a little below the chamfer edge); I waited almost 4 days for the Loctite to fully cure. Knock on wood, it's holding so far.

I'll just add that I talked to a Loctite/Henkel technical rep after the machine shop used Loctite 518. The rep said that Loctite 540 is what they recommend for core/freeze plugs. When I googled it, I found that 540 is prohibitively expensive (because it is only sold in a relatively large bottle). I talked to Loctite again, and they said that Loctite 262 would be their next best suggestion, but without any use history; it's available in smaller quantities more economically.

 

[macleanflood]

Wow...

-Mac