396/425 Block Coolant Drain Plugs...What Type???

[James W.]

Can someone tell me what type the factory correct coolant drain plugs found in the engine block on a 396/425 engine just above the oil pan rails are?

Are they a recessed, square head, a recessed, hex head or a square, outward protruding plug? Same question for the plug found in the lower left front corner of the block, just above the oil pan rail.

Thanks,

James West

[Joe L.]

Re: 396/425 Block Coolant Drain Plugs...What Type?

James-----

The coolant drain plugs above the oil pan rails were 1/4" NPT with external hex head and they were steel. They were available until recently from GM under GM #3889330 but they are now discontinued. You should be able to find suitable replacements in a hardware or auto parts store. I prefer BRASS for these. When painted with the block, they look pretty much like the originals.

The plug in the front of the block near the oil pan rail is a different story. This is the plug for the block's main oil gallery (Mark IV big blocks, EXCEPT ZL-1, have the main oil gallery just above the driver side oil pan rail). I THINK that this plug is an internal, square head 1/4-18 NPT plug. IF SO, I think that GM #144011 will do the trick. It's still available. Check the size first, though, to be sure it's 1/4-18 NPT.

[Clem Z.]

Re: 396/425 Block Coolant Drain Plugs...What Type?

all the front oil galley plug are 1/4" NTP but some blocks used 1/8" NTP plugs in the side of the block for the oil gallery and these were internal 3/16" square. i used 3/16" square lathe hardened tool steel bits to remove and install these plugs