Some two-stroke oil advocates advise the addition of two-stroke oil in small quantities (500 ml/tank) in the fuel tank of petrol and diesel engines. This is a hot topic on many 4×4 forums. I accept that doing so can have some positive effects, but could you please tell me what effect two-stroke oil might have specifically on lambda sensors and catalytic convertors?
PHILIP LOCHNER, Via email
Answer: Without conducting actual testing, we can merely speculate on the impact that two-stroke oil has on lambda sensors, catalytic converters and diesel particulate filters. The fact remains that adding two-stroke oil is completely unnecessary (as fuel from the main oil companies already have all the necessary additives) and often does more harm than good. The durability testing programmes to which automakers subject their vehicles’ engines are run on certified fuel without “special” additives such as two-stroke oil. Therefore, you’re entering unchartered territory when you add your own mix to legislated fuel.
Sasol performed testing on diesel containing two-stroke oil at its Fuels Application Centre in Cape Town (see the technical feature in October 2013) and showed that there is no measurable increase in lubricity when two-stroke oil is added to diesel. In fact, diesel base fuels that are sold by the refineries have to comply with a strict lubricity specification and in many cases they are already supplemented with special lubricity-improver additives. Furthermore, two-stroke oil contains certain metallic compounds that are known to cause injector fouling in modern common-rail diesel engines. Engine-test results showed significant injector fouling and an associated engine-power loss when two-stroke oil was added to diesel. This practice is therefore best avoided