An internal combustion engine having an improved oil treatment system. The internal combustion engine may be a splash lubrication engine in which oil is flowed through an oil circulation circuit by a passive pump. In another aspect, a dipstick tube may be provided that includes a portion of the oil circulation circuit. In a further aspect, the internal combustion engine comprises one or more protuberances that automatically penetrate an oil treatment apparatus upon the oil treatment apparatus being mounted to the internal combustion engine, thereby fluidly coupling the oil treatment apparatus to the oil circulation circuit.