Sealing between piston rings and the cylinder wall may be the result of which condition?

• A. Low cooling water temperature
• B. High coolant temperature
• C. High oil viscosity
• D. High carbon residue in the oil

Answer: (B)

Sealing between piston rings and the cylinder wall is controlled by the combination of ring pressure against the bore and the lubricating oil film that keeps surfaces separated. When the coolant temperature is high, the engine runs hotter, and the piston (typically aluminum) expands more than the cylinder wall (usually iron or steel). This reduces the clearance between the ring and the bore, so the rings press more tightly against the wall and the oil film is more effectively squeezed into the gap. That tighter fit helps create a better seal and reduces blow-by. Of course, excessive heat can cause other problems, but the hotter condition can tighten the fit and improve sealing under normal circumstances.