The sinuses are air-filled cavities. 1  They are located: 2  Within the bony structure of the cheeks. 3  Behind the forehead and eyebrows. 4  On either side of the bridge of the nose. 5  Behind the nose directly in front of the brain.
An O-ring is a round ring that is used as a gasket for sealing a connection. O-rings are typically constructed out of polyurethane, silicone, neoprene, nitrile rubber or fluorocarbon. These rings are commonly used in mechanical applications, such as pipe connections, and help to ensure a tight seal between two objects. O-rings are designed to be seated in a groove or housing that keeps the ring in place. Once in its track, the ring is compressed between the two pieces and, in turn, creates a strong seal where they meet.
The O-rings in question are the large ones that are responsible for providing the seal between the alternating steel and aluminum sections of the engine. There are two sets of O-rings at each section joint--an inner one and an outer one. These O-rings function to keep coolant flowing through the passages from section to section. The outer O-ring keeps coolant from leaking to the outside of the engine.