A woman who consistently put the wrong grade petrol in her car, causing serious engine damage, has lost a bid to make the dealer take the car back.

Suzanna Chan bought a 2010 Volkswagen Golf from Top Motors Plus in March 2018. A year later it suffered significant engine damage, and she tried to return the car to the dealer, saying the vehicle had not been of acceptable quality.

Top Motors Plus agreed the car's engine needed expensive repairs, but it denied liability, claiming the damage was caused by Chan using the wrong fuel.

The case ended up before the Motor Vehicle Disputes Tribunal, which in a just-released judgment said the dealer was not to blame, and was under no obligation to warn people about the need to use the correct fuel. It noted, however, that the dealer had told Chan to use the correct fuel.

Chan told the tribunal the car suffered significant engine damage in April, 2019. She took it to a garage which found cylinder and piston ring damage, with one of each broken and the others also needing to be replaced. Repairs were estimated to cost $4950 plus GST.

Chan suggested the engine damage may have been caused by an inherent or pre-existing defect, inadequate past servicing and because Top Motors Plus did not service the vehicle before it was sold to her.

"The evidence does not support this theory," the tribunal said in its decision.

Firstly, there is no evidence to show the vehicle had an inherent defect at the time of sale, and the evidence suggested Top Motors Plus serviced the vehicle before it was supplied to Chan.

Instead, the tribunal said it was satisfied the engine damage was caused by Chan using 91 octane fuel.

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Chan and her partner Theo De Villiers gave evidence that they predominantly used 91 octane fuel in the vehicle, with De Villiers saying 91 octane fuel was used about 85 per cent of the time.

The tribunal said that model Golf must use 95 octane or higher fuel. Using 91 octane fuel can cause pre-detonation in the engine's combustion chamber that then damages the engine's pistons and rings.

Chan's car had a crack in a compression ring on one of the pistons, damage the tribunal found was almost certainly caused by using 91 octane fuel.

The tribunal's expert also said the damage must have occurred during Chan's ownership, because if the engine was damaged before she purchased the vehicle the damage would have become apparent much sooner.

Chan and De Villiers argued they did not know they needed to use higher octane fuel and that Top Motors Plus should have explicitly told them that they needed to use higher octane fuel.

The tribunal accepted the dealer's evidence that he did tell them they must use 95 octane or higher fuel.

"Further, even if Top Motors Plus had not told Ms Chan and Mr De Villiers that the vehicle required 95 octane or higher fuel, I do not consider that Top Motors Plus had an obligation to do so. I consider that it is the consumer's responsibility to make the necessary inquiries to determine what type of fuel should be used in a vehicle, in much the same way as they should make inquiries as to the type of oil, brake fluid or transmission fluid that should be used if they are putting those substances into a vehicle."