Its that time of year so I pulled the block drains yesterday, and when I did the 1/4" NPT fitting on the stbd side of my stbd motor screwed out with it. As usual the motors didnt drain immediately so I reached under with a small screwdriver to poke through the crud. There are a few holes down there on that side of the stbd motor and I wasn't sure which one it was since the 1/4" NPT had come out, so I poked around in each until the blockage cleared and it drained out on that side. All good! (nope)...

When I put the NPT fitting and plug back in and ran antifreeze, pink was dripping down into the bilge from the bottom of that engine. Huh? I felt around and realized it was dripping out of the slightly smaller diameter hole right next to the block drain. I was totally confounded trying to figure out what was going on, and trying to get the fitting into a too small hole until I realized I could get my phone under there and take pictures of it.






It appears this second hole almost makes it to the water jacket and I poked through it with the screwdriver, which didnt take much force at all. Can I just fill this up with JB Weld (or their steelstik product which I read works on damp metal)?

I bought this used block last year to have this motor rebuilt. I dont think my other block has that 2nd hole there next to the drain plug, is this unusual? Do some blocks come with an extra hole or did someone drill it in the past to mount something (knock detector for example)? Would it be caused by excessive corrosion inside the block or more likely is it because someone drilled that hole too deep?

the one closet to the pan rail is the block drain, someone drilled and taped the other boss.........using the upper drain hole will not allow all the water to escape for winterizing

Exactly that’s crazy!

you screwed the drain in to the knock sensor pad.
you can see the thread in the boss by the pan rail.thats were the drain needs to go back in.

were he screwed back into is dry,nothing ever came out of there.

I would run a tap into it, then put a bolt into it with thread sealant. JB weld alone wouldnt make me feel safe.

Thanks for the feedback gents

Bottom hole for full drainage, makes sense.

Yeah I wondered if that top one was for knock sensor. Explains no water coming out of it.

Now that I know this one is definitely the drain i'll have to try tapping it since there is no way the 1/4" NPT is getting in there. Hoping I can get it in there straight and tap it true. Gonna be fun :/

it should screw right back in the hole it just came out of i would think.

1/4" NPT tap sorted it out. Thanks everybody.

All the knock sensors I have seen were always mounted in the drain hole with T and plug was on other side of the T. Big blocks small blocks Mercruiser ad Volvo. Glad you got it fixed👍