Hello, please tell me what this bolt is for on the D1ZY8 engine eight engine(upper left of the oil filter). Thanks.

 

Crankcase core plug. Just a cap to cover the hole in the crankcase left from the manufacturing process.

 

Thank you, Sir Ryan!

 

Looks like the coolant drain bolt on the block. It leads to the bottom of the coolant jackets around the cylinders, behind cylinder #2. You can see the light behind cylinder #2 in the bottom of the coolant jacket, in the picture, from a flashlight in the drain hole. The blue shop rag, on the pulley side of cylinder #1, is in the inlet from the water pump.

(pg 10-7, '96-'00 Civic Service Manual)