Need to find a suitable oil for your classic? Here’s how you need to choose the best lubricant for your engine
There are surprising loyalties at work with engine oil, be it to a brand or even a colour. Not for nothing is Comma Classic 20-50 green, like Duckhams used to be. There’s a lot of misunderstanding, too.
Some say you should use oil as close as possible to what was used in your classic car’s engine originally, perhaps a basic 20W/50 without much in the way of additives. Others will tell you to use the most modern synthetic oil you can, with the low viscosity and squeaky-cleanliness needed for today’s thrashed repmobiles.
Well, finding an oil exactly like oils were 40, 50, 80 years ago is hard. Good thing too. Engines coked up and wore out much more quickly then, and the oils were a major reason why. Newer oil cocktails are better able to resist oxidation and stay thick when you need them to, while being thin when you want them to. So the oil flows quickly when it’s cold, reducing wear after a cold start, but still keeps moving metal surfaces apart when it’s hot.
What you need, then, is the oil the engine’s designers would have liked, had it been available. That’s oil which embraces the originally specified viscosity range, to suit the clearances and oil-pumping efficiency with which the engine was designed (although being thinner when cold – a lower ‘W’ number – is no bad thing). What it does not mean is a super-clean, super-runny oil as is used in the latest tight-tolerance modern engines.
If you used that in, say, your Lotus Twin-Cam, it would burn off, leak out, reduce the oil pressure and, crucially, cause the bucket tappets to wear out. That’s because oils for modern engines have little or no ZDDP (zinc dialkyl dithiophosphate), an anti-scuffing agent which, inconveniently, is poisonous to catalytic converters. Our engines need at least 1000 parts per million of it in their oil, and oils intended for classic cars oblige.
Most classic oils, too, are mineral based whereas the best modern-car oils are synthetic. Synthetic oil is more expensive, and its longer-lasting abilities aren’t necessarily needed in relatively little-used classic cars. That said, it keeps its viscosity better when really hot and stays cleaner.
Synthetic or semi-synthetic oils with classic-friendly viscosity ratings and plenty of ZDDP do exist, one of them specified at a remarkable 15W/60. The perfect classic oil, or overkill? That’s between you and your engine.
Words: John Simister