Forum

[Presto]

What I don’t understand is why older engines, operating at far lower stresses than more modern high performance engines, need the extra protection that a zinc component in the oil provides. And how ‘old’ does an engine needs to be before it needs this extra protection?

[Barry N]

That's a good question Presto! From what I have read elsewhere, the flat cam-followers (tappets) in many old car engines (and our Bullets) are particularly prone to wear unless there is sufficient zinc content in the oil. And as Leon said, when catalytic convertors came in on the cars, the zinc content was reduced in most motor oils without adverse affect on modern car engines. The classic car boys are well up on this stuff, so I use classic formula oils such as the Halfords one (or the Castrol Classic range) just to be on the safe side.

[Presto]

This is something that interests me! The (very good) article eddie mentions says (rightly) that zinc, as an anti-wear additive, ‘only comes into play as a last resort when the oil boundary layer has broken down and metal to metal contact occurs’. What I don’t understand is how sophisticated modern oils, developed for highly stressed modern engines, are ever likely to ‘break-down’ when used in old very, low stressed engines. It’s sometimes pointed out that cams, camshafts, and tappets put oil under enormous sheer and other stresses. No doubt that’s true, but isn’t it equally true that those components will generate even greater stresses in modern high performance, high revving engines?

[Mark M]

One big difference is that modern engines use hydraulic tappets removing one big area of stress. Also, I've noticed that Morris oils are stocked in our local Farmer's Supermarket (Countrywide) apparently because so many old Land Rovers run on it!
REgards, Mark