New emission requirements for compression ignition engines have led engine designers to review the attributes of positive valve stem seals. Federal standards for particulate emissions were initiated in 1988 for heavy duty diesel engines in the United States. Since then, the standards on particulates have been significantly reduced from .6 g/kW*hr in 1988 to .1 g/kW*hr for 1994 *. Lowering particulates, improving oil economy and reducing guide wear have all become important issues in the heavy duty engine marketplace. All of these factors are affected, in part, by the amount of oil flowing thru the clearance between the valve guide and valve stem. Bench tests indicate that heavy duty valve seals could reduce overhead oil consumption by as much as 99% during idle/motoring conditions and lower particulate emission levels contributed by lube oil up to 75%. In addition, they can significantly reduce guide wear and valve stem scuffing under turbocharged conditions.