I’ve heard I can’t use synthetic motor oil in a classic car?

The debate around whether you can use synthetic motor oil in a classic car gets quite emotional; with many owners and collectors laying out a lot of money on their cars it’s bound to whip up strong emotions.

Taking out the emotion; the supporters of not using synthetic engine oil in a classic car point to the fact that modern oils, including most synthetic oils, have drastically reduced (or no ZDDP) levels of ZDDP (zinc dialkyldithiophosphate). This is necessary because the zinc in the oil damages the
catalytic convertor and lambda sensors fitted to modern cars.

Zinc in ZDDP is a sacrificial additive that protects, mainly, the valve gear from high pressure friction, which can generate rapid wear.

The other problem classic car owners may encounter is that of compatibility with some of the older oil seal materials. These old style seal materials may be impacted negatively by PAO and or ester technology oil, which could cause swelling and eventually oil leaks.

So without ZDDP it wouldn’t be wise to use synthetic motor oil in a classic car?

A classic muscle car with high lift camshafts would certainly need ZDDP to protect the valve gear against the frictional wear that the high pressures would generate. However if you had an engine that ran a roller follower, where the pressures are a lot lower a synthetic engine oil may work just fine.

Some synthetic lubricants manufacturers such as Habot Synthetic lubricants actually have a synthetic oil with ZDDP added to cater for these applications. The Habot product carries the designation ZN+ and would be the best synthetic motor oil in a classic car.

There are also synthetic and semi synthetic oils that do contain traces of ZDDP, in the 800 to 1000 PPM range that also offer some protection against valve-train wear.
 
However it’s not the fact that oils are synthetic that they contain limited amounts of zinc, even modern regular motor oils are restricted to lower levels of the additive.

Are there any advantages to using synthetic motor oil in a classic car?

Classic cars tend to be driven much less than your every day vehicle and so they tend to spend extended periods without running. During the cooling down process it’s quite normal for moisture or condensate to form in the crankcase. However this moisture tends to collect in the sump where it comes into contact with the motor oil.

Regular mineral oil has paraffin’s, waxes and traces of Sulphur, which occur naturally in crude. With the classic car’s engine standing for extended periods the water and sulphur react to form sulphuric acid which is obviously highly corrosive.

Synthetic lubricants, with engineered base stock, contain no sulphur and therefore there’s no danger of corrosion.

Another advantage of synthetic engine oil in a classic car is that, because the lube is more temperature stable it’s possible to run a lower viscosity, which means that on start up the oil reaches the cylinder head quicker thereby reducing cold scuff.

Whether or not you choose to use synthetic motor oil in a classic car or stick with regular engine lubricant it’s always advisable to follow the recommendations of a quality oil supplier; such as Habot Synthetic Lubricants who produce quality synthetic lubricants for a wide range of applications, including classic cars.