I looked through my manuals and I couldnt find any diagram that showed what each hole was used for in the engine block (as seen from the cylinder head mating surface).

I was kinda worried about this one hole because it seemed to be completely filled in with some sort of powdery stuff. It almost looked like dirt, with some small rust particles sprinkled in it.

My question is, what is this hole used for? Water passage? Oil passage? useless hole?

see picture:

I believe that it is a Water passage. I looked at a spare cylinder head that I have here, and observed that the hole in the cylinder head that would be directly above that hole in the block seems to be a water passage. I can shine a light in one hole and can see the light in the next hole.

I don't think there are any "useless" holes in the mating surface of the block/head.

**There is a hole in the top of the block that appears to be plugged up, except for a small pin hole in the center, but it isn't the one your arrow points to.

I recon its a head allignment thingamebob.

It usually has a metal thing, like a piece of tube with a split down the side, and with bevelled ends, and correspinding hole in the head for it to fit into.

Its so that when you drop the head on it is aligned correctly, and doesnt move around when you are tightining head bolts.

Just my guess.

Sounds logical to me. Ive pulled apart two engine this year and both had that hole. Dont ask me.:stupid:

Inf;

here is a picture of one of my spare L24 blocks. I've labeled most of the holes found in the area of your picture. The hole you marked with a green arrow is a water jacket hole. It should be open (not plugged).

Ah, thanks for that info Carl.

Guess i'm gonna have to poke around and see if I can figure out why its plugged up, and maybe clear it out. I plan on flushing and backflushing the whole system extensively when I slap the head back on.

As far as I can tell the bottom end is OK at the moment and should last me just fine until I get together the motor i'm aiming for this winter. The original head was run on unleaded I guess, so the original intake seats were beaten up into the head.

Your welcome.

If you can get a vacuum to the engine, hold the business end of the vac near the plugged hole with one hand, and pick at the plug material with a nail, or other utensil. Anything that comes loose will get sucked into the vac instead of falling into the block.

It could be that someone put a "Stop-leak" chemical in the cooling system and it gunked up that hole, or maybe the motor sat for a while and sediment collected there. Anyway, I would definitely suggest clearing it before assembly.