While European motorists have had the choice between 95 and 98 octane unleaded petrol, South Africans are still stuck choosing between 93 and 95, and while these numbers seem arbitrary to some, there are key differences.
These differences also determine which vehicles benefit from each fuel grade, as high-performance, high-compression vehicles like turbocharged or supercharged cars benefit from higher-octane unleaded petrol.
Lower-compression naturally aspirated motors gain no noticeable benefit from using lower-octane petrol, besides marginal cost savings – around 20 cents per litre inland right now.
South Africa’s biggest petrol producer, Sasol, says the octane rating of petrol refers to the fuel’s tendency to ‘autoignite’, and a higher number indicates a slightly reduced autoignition tendency.
Simply put, a fuel’s octane rating represents how likely it is to resist auto- or pre-ignition, which can cause pressure spikes, or ‘engine knocks’, that damage engine components over time.
The higher this rating, the more controlled the fuel burns under high compression, making it suited for more powerful, high-compression vehicles.
According to insurance company Dotsure, 1.6-litre motors tend to be the separator, with motors of this size and smaller not benefiting from 95-octane petrol.
“If you’re chugging along in a 1.8-litre, you might feel a tad more oomph with 95,” the insurer clarified.
“However, it’s in larger engines such as 2.0-litre turbo and V6 where the difference in performance is most noticeable, and manufacturers recommend using only 95 octane or higher.”
Sasol adds that the difference between the 93 and 95 octane rating is relatively small and, contrary to popular belief, does not refer to the energy content of the fuel itself.
The colour differences between the two fuel grades come down to dyes added after production, purely to make identification easier.
According to Sasol, both are identical after production, with 95 dyed green and 93 dyed yellow for identification purposes within the logistics system.
Deciding what to fill your car with
Major automotive retail group, Motus, explained that when it comes to choosing between the two, it all boils down to what you drive.
“For most cars, performance requirements don’t vary too much, but a supercar or a turbo not only gulps up a lot of petrol, but it also needs a higher quality of petrol to perform at its best,” it explained.
“If you drive a sedan, a hatchback or any standard car, 93-octane petrol will work perfectly. Should you own a veritable speed demon, however, you’ll need to fill up with 95 octane.”
The retailer added that should your car run on 93-octane unleaded fuel, and you fill it with 95, it will still run, and the fuel won’t damage the engine or affect it in a way that may require a visit to a vehicle repair workshop.
“The only harm would be to your bank account, as 95 is costlier,” Motus explained.
According to the dealer group, 95-octane fuel may even offer you better mileage than 93 petrol if you drive a regular car.
“If you have a supercar and fill up with 93, you’ll find your car underperforms as the fuel quality isn’t quite as good,” it added.
Crucially, there won’t be any permanent damage, but motorists who want to be completely sure what fuel to fill their cars with are encouraged to check their car’s fuel cap or handbook.
“While the general rule is that you won’t need better than 93 octane, where you live or the environment in which you are driving impacts your car’s performance,” said Motus.
“Factors such as environmental conditions, like the weather, and the altitude you are driving at may mean that a different octane petrol could be more beneficial.”
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