either 10-30 or 10-40 depends on what part of the country you live in.
Most carwashes have an Oil Change center. You should probably take it there/
You have a blown head gasket or a cracked head.
5 QTS. with a new filter.
There is no "oil cam sensor". There is a oil pressure sensor and a cam sensor, but they are two different sensors.
The oil pressure switch on a 1998 Chevy Blazer is on the side of the engine block. It is located above the oil filter.
Oil pan.
on the oil pan...
in the oil pan
The oil cap on a 1998 Chevy Blazer is located on the passenger side of the motor. It is just to the left of the manifold cover.
inside the oil pan
The engine oil drain plug would be at the lowest point on the bottom of the oil pan. It should take a 15mm wrench to remove it couterclockwise.
5w30