I have a 1984 D-100 p/u truck w/ 318 engine. I was able to remove the engine block coolant drain plug w/o breaking it, however; the threads are very marred up. Surely I'll need to rethread the block's drain plug hole & put in a new drain plug, but I'm leary about giving it a shot w/o knowing the thread size. Does anyone know the thread size? Thanx.

 

Which threads are chewed up? In the block or on the plug itself. If they are still good on the plug any hardware store will have a gauge that will tell you the thread and pitch. Just take it to them and they can put the gauge on it.

 

Thanx for responding. Generally when a bolt is removed & it's thread is marred, the bolt hole it was secured into needs to be repaired as well. Getting a thread count & pitch will be impossible to read from the old engine block coolant drain plug/ bolt due to being extremely marred.
After removing it, I was dumbfounded that it did comletely snap when removing it.

 

another option may be Heli-Coil the drain openingg and get a new plug.