Consumer Watchdog: Fooled by fuel myth

High-octane fuel can bust the budget for little benefit. Photo / Thinkstock

If you're lucky enough to drive an Aston Martin or Ferrari, the cost of high-octane fuel probably won't blow your budget. But many motorists are shelling out up to 15c extra a litre for premium petrol when it offers little or no benefit to most cars in New Zealand.

Motor Trade Association spokesman Ian Stronach said a car designed for regular unleaded 91 fuel would be no better off with 95 octane, and a car designed for 95 would be unlikely to get any significant benefit from the ultra-expensive 98-octane products. Typically, 95 octane was about 7c dearer per litre and 98 was 15c more than 91.

"There's this suburban myth that suggests a bigger number is better, no matter what car you drive," Stronach said. "You're just costing yourself money. Around 90 per cent of cars in New Zealand are designed for 91. Few cars really require 98."

Conversely, some drivers were filling up with cheaper, low-octane petrol when their cars were designed to run with 95- or 98-octane fuels.

Automobile Association PetrolWatch spokesman Mark Stockdale said this could put pressure on the engine and cost more through repairs. "The best fuel to use is the one the engine was designed to take."

The octane level related to how much pressure the fuel and air mixture could tolerate before the spark plug ignited it. Although few models required 98 octane, BP communication manager Di Papadopoulos said the company was scrambling to meet demand.

"This year we have increased the number of stations where it is available," she said.

The marketing of premium fuels such as BP Ultimate, Caltex Premium with Techron, Shell V-Power, ZX and Mobil Synergy was based around claims that added detergents "cleaned" the engine.

Papadopoulos said high-octane fuels could keep an engine "virtually as clean as when it was new, even if it was designed to run on regular 91".

She said independent tests commissioned by BP found many vehicles running on regular unleaded fuel had significant carbon deposits in the engine which could contribute to a reduction in performance, and BP Ultimate removed up to 61 per cent of these deposits.

Stronach said motorists with cars using 91 fuel could be assured they were not clogging their engines.

"You don't have anywhere near the carbon build-up you used to see in the 60s and 70s."