Advice needed : messed up the radiator drain plug thread
 

Hello, I guess I could have posted this in the newbie section but since I wasn’t sure I went for this place.

When doing a coolant change two weeks ago I very stupidly messed up my Koyo rad drain plug. I am not sure if I overtightened it or missed a thread but after the coolant drain and running the engine with water I took the drain plug off as I was about to put some new coolant back in and realized it was damaged (felt really loose and didn’t want to come in the same way than before).

I quickly re-ordered a new drain plug and when trying to screw it by hand I had some resistance (inside thread must have been damaged as well, don’t know how much). I then stopped and decided to seek advice as I am not a seasoned mechanic.

I am seeing the following options here:

1_ buying a new rad: well I don’t have the time and money I used to have when I bought this car so if there is a better option I’d like to avoid it.
2_ re-threading the rad drain hole: I have never done it but I guess I could find help and have it done but I don’t know if this will seal well
3_ re-threading the rad drain hole and plug it permanently: I don’t know if that is possible, that would make the next coolant change uneasy I guess but could work as a temporary measure

You can find the picture of the new and damaged drain plug if that can help.

By the way I track the car a few times per summer so it has to be robust.

Thanks for your advices.

Joel

The initial plug appears to have taken quite a bit of material out with it so retapping it may be an issue, I would look locally for a radiator shop they could possibly weld a new bung on there for you and be able to pressure test it for you

You can buy a larger drain plug. The radiator will be simple to drill larger and re tap to a larger size. Just don't use a NPT plug, those are tapered and can crack when over tightened. Get a straight cut plug like an ORB or one with a crush washer. I suggest looking through the caps and plugs section at anplumbing.com.
Good luck.

Tap for a larger brass fitting that can accept a plug in the middle. When inserted use epoxy to insure that it stays in when removing the smaller plug.

The Koyo plugs are made of very soft aluminum as I had a similar problem while not even over tightening it. The female threads are hard aluminum.

Thanks silverTRD and Rikk for your feedback it is much appreciated!!!