Omix Valve Stem Seal Set- 11-21 WK/JK 3.6LOil fouled spark plugs or that dreaded blue smoke coming out of the tail pipe could be a sign of failing valve stem seals. Valve stem seals provide a controlled leak of oil to allow the valve stem to be lubricated as it slides in the valve guide. The amount of oil that passes by the valve stem seal must be precisely controlled. Too little oil causes stem and guide wear. Too much oil causes carbon buildup; leading to valve seat damage and other issues.