The Effects of Engine Oils on Intake Valve Deposits and Combustion Chamber Deposits

Short deposit sampling procedures were employed in a single-cylinder CFR engine to investigate the potential which an engine oil or an oil component has for forming deposits.

Both valve temperature and oil flowrate on a valve have significant effects on an oil's deposit forming tendency. However, the formulation of the oil is the dominating factor that determines whether an oil will keep a valve clean or form heavy deposits. Among the oil components, oil detergents, dispersants, and VI improvers are major contributors to intake valve deposits, while high-boiling base oil can keep a valve clean.

The deposit forming tendency of an oil in a combustion chamber is very different from its tendency to form deposits on an intake valve. Higher oil consumption rates and higher base oil boiling ranges tend to increase the deposit level in a combustion chamber.