Why you shouldn’t use synthetic motor oil in older engines!

Over the past decade the internal combustion engine has come a long way leading people to believe that they can’t use synthetic motor oil in older engines. This is a statement that is, to a large degree, true, but it’s important to understand the intricacies behind this.

The use synthetic motor oil in older engines can lead to problems.

In order to understand why you might not be able to use synthetic motor oil in older engines we need to look at the modern engine and emission control. Since the 1970’s the world has taken note of global emissions, with OEM’s implementing several measures to reduce vehicle emissions. The one that influences the use of synthetic motor oil in older engines is the introduction of the catalytic convertor.

The precious metals used as a catalyst in these systems are susceptible to poisoning by lead and zinc, amongst other metals. In order to ensure longevity of the expensive catalytic convertor fuel companies have moves away from boosting fuel octane ratings with lead, while at the same time oil manufacturers have ceased to add zinc to their motor oil (Or drastically reduced this zinc as an additive).


Zinc has long been an additive in high performance engine oils because of it’s excellent lubricating properties under high load conditions, such as found in the contact between camshaft and valve gear (Buckets, rockers etc.)

The removal of zinc from modern engine lubricants (It’s not just synthetic motor oil that has reduced levels of zinc, regular motor oil also contains no zinc) therefore has an effect if you use synthetic motor oil in older engines.

When can you use synthetic motor oil in older engines?

It’s important that you understand that it’s not the synthetic oil that’s incompatible with older engines (Although some older seal materials tend to swell when coming into contact with synthetic polyalphaolefin engine oil).

There are several oil companies that sell specially blended synthetic engine lubricants containing reduced levels of zinc specifically so that you can use synthetic motor oil in older engines. Obviously it’s important that the vehicle is not equipped with a catalytic convertor in this instance.

It may also be possible to use synthetic motor oil in older engines where the valve gear loadings aren’t high. This however, can be risky, as the only tell-tale signs that you can’t use synthetic motor oil in older engines will be excessive wear of the valve gear.

It’s therefore that if you want to know if you can use synthetic motor oil in older engines you contact a professional lubricants supplier, such as Habot Oil, who produce high quality synthetic lubricants.