| abstract |
An exhaust valve seat in a natural gas fuel internal combustion engine is prevented or suppressed from retreating. An engine is lubricated with a lubricating oil composition comprising (a) a relatively large amount of oil of lubricating viscosity and (b) a relatively small amount of a natural gas engine oil additive package. However, the lubricating oil composition is substantially free of any zinc compounds and alkaline earth metal salts of condensation products of alkylene polyamines, aldehydes, and substituted phenols. [Selection figure] None |