New Engine Block Coolant Drain Plugs
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From: Clayton MI
12 point in a pinch....
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Joined: Jun 2019
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Mission Accomplished
Well, after much learning, cursing, and busted knuckles I got new plugs back in. I'm going to write up how I did it to help the next unfortunate amateur mechanic.
After regrettably removing both engine block coolant drain plugs, both plugs had damaged threads and were full of gunk. I bought new plugs, which are brass, 1/4" NPT pipe plugs with a 9/16" head.
There were deposits and gunk from over the years in the threads of the drain holes, which kept me from threading new ones in. By hand, I used a 1/4" NPT pipe tap with a bit of wheel bearing grease smeared on the threads (not the flutes) to clean out the holes. The wheel bearing grease acted as lubricant and also captured the gunk I was getting out.
Thread the tap in the plug by hand until you get resistance, back it out a bit, thread it back in. Remove the tap completely. Clean off the tap with a brush and a towel, reapply the grease, then do it again. Keep doing this to clean the threads until you feel the tap bottom out in the hole. Don't use a wrench for the tap, or you might risk messing up the threads or going too deep.
Finding new plugs was a pain in the butt. Go to a specialty fastener store and have them get the correct plug. I measured and remeasured the old and new plugs with a digital caliper to compare them. Both had an outside diameter of around 13.5 mm, were approximately the same length, 18 thread pitch. Confirm your tap is the same dimensions by 1) reading the 1/4"-18 stamped on the tap, and 2) marry the threads of the tap with the threads of the bolt: if no light shines through when they match up, you're good.
Apply some Teflon tape to the new plugs. Get them started by hand into the drain plug, they probably won't go in very far. Finish it off with a 6-point 9/16", 3/8" drive socket. You can use a 12-point socket up to a certain point, but a 6-point will reduce the risk of the socket slipping and rounding the head (ask me how I know).
I managed to bottom out one plug. The other plug went about 90% of the way in. I did not torque it any further, for risk of shearing the head. If the plug is threaded so tight I can't safely tighten it anymore, it's doubtful any coolant will be able to leak around those threads, especially with the Teflon tape.
NOTE: I managed to get the socket stuck on the plug a time or two. The wrench went sideways and the socket twisted around the head, getting it stuck. It's difficult to remove it working in such tight quarters. I used a small hammer to gently tap the driver-side of the socket to get it wiggling around, then it popped right off.
I haven't ran coolant through yet since I'm still in the process of replacing hoses, so I haven't torture tested my work. I'll update if I have failed but I'm confident it will work!
After regrettably removing both engine block coolant drain plugs, both plugs had damaged threads and were full of gunk. I bought new plugs, which are brass, 1/4" NPT pipe plugs with a 9/16" head.
There were deposits and gunk from over the years in the threads of the drain holes, which kept me from threading new ones in. By hand, I used a 1/4" NPT pipe tap with a bit of wheel bearing grease smeared on the threads (not the flutes) to clean out the holes. The wheel bearing grease acted as lubricant and also captured the gunk I was getting out.
Thread the tap in the plug by hand until you get resistance, back it out a bit, thread it back in. Remove the tap completely. Clean off the tap with a brush and a towel, reapply the grease, then do it again. Keep doing this to clean the threads until you feel the tap bottom out in the hole. Don't use a wrench for the tap, or you might risk messing up the threads or going too deep.
Finding new plugs was a pain in the butt. Go to a specialty fastener store and have them get the correct plug. I measured and remeasured the old and new plugs with a digital caliper to compare them. Both had an outside diameter of around 13.5 mm, were approximately the same length, 18 thread pitch. Confirm your tap is the same dimensions by 1) reading the 1/4"-18 stamped on the tap, and 2) marry the threads of the tap with the threads of the bolt: if no light shines through when they match up, you're good.
Apply some Teflon tape to the new plugs. Get them started by hand into the drain plug, they probably won't go in very far. Finish it off with a 6-point 9/16", 3/8" drive socket. You can use a 12-point socket up to a certain point, but a 6-point will reduce the risk of the socket slipping and rounding the head (ask me how I know).
I managed to bottom out one plug. The other plug went about 90% of the way in. I did not torque it any further, for risk of shearing the head. If the plug is threaded so tight I can't safely tighten it anymore, it's doubtful any coolant will be able to leak around those threads, especially with the Teflon tape.
NOTE: I managed to get the socket stuck on the plug a time or two. The wrench went sideways and the socket twisted around the head, getting it stuck. It's difficult to remove it working in such tight quarters. I used a small hammer to gently tap the driver-side of the socket to get it wiggling around, then it popped right off.
I haven't ran coolant through yet since I'm still in the process of replacing hoses, so I haven't torture tested my work. I'll update if I have failed but I'm confident it will work!