The development of engine oil additives - ZDDP

A guest article from our friends at first published in Classic Car Africa…

Castrol was established in 1899 and has over the years amassed huge expertise in oil technology. Motor manufacturers worldwide trusted the formulations which were tried and tested and then recommended in owner’s handbooks. In recent years oil specifications have changed dramatically, following new emission controls and the different requirements of the ‘modern’ engine. Many new formulations have appeared and resulted in confusion about whether modern oils are suitable for older engines. However, the oil formulations required for today’s vehicles are very different, having thinner viscosities and different additive technology that is generally unsuitable for an older engine, as well as having a synthetic rather than mineral base. One of the important additives for older engines, found in classic oils, is Zinc Dithiophosphate – known as ZDDP.

ZDDP additive provides a high level of anti-wear protection, but its phosphorus content is harmful to catalytic converters and other emission equipment fitted to many modern vehicles. It has therefore been reduced in modern oil specifications, which are designed for engines with the latest surface hardening technology and to meet the latest emission requirements – which also necessitate the use of other emission friendly additives which are not designed for use in classic engines.

In the late 1940’s the Spitfire aircraft engines were experiencing severe camshaft damage and failures. As a critical fighting machine during the war it was essential to overcome these issues. Castrol was asked to investigate and what developed was the addition of Zinc Dithiophosphate. The effect of ZDDP is that, when hot, it interacts with the iron of the cam lobe, thus creating a sacrificial layer between moving parts. This prevents metal-to-metal wear. The addition of ZDDP to oil reduces premature failure of the cam and lifter. Castrol Classic oils contain the correct amount of ZDDP additive to protect your veteran, vintage, or classic engine.

Jaguar E-type engine bay
Technicaldan ormeZDDP, additives