"Hand on heart, I know I haven't put any petrol in my diesel truck," says Lizzy Smith.
But the workshop has been just as adamant - fuel contamination did the damage.
Smith's 2017 Ford Ranger has been off the road for four months while she disputes that cause with South Auckland Motors.
The turning point has been coming to Fair Go with the results of a fuel sample test that the dealer and service agent claimed was confirmation of contamination, but which experts Fair Go spoke with say is anything but.
Engine trouble
The truck suffered a sudden mechanical failure in January, complete with loss of acceleration, black smoke and a shuddering, knocking engine that stopped.
Smith contacted South Auckland Motors. It had sold her the ute four years and 45,000 kms ago and serviced it fully each year - so she thought it would want to investigate.
The workshop said it couldn't book her in, so Smith went to another garage, Tony Allen Auto Service, which has run WoF checks on the truck before.
It worked on the vehicle for two-and-a-half hours, and concluded the engine might need to be replaced at a cost of up to $14,000. That was just an initial diagnosis, so more work needed to be done to determine the exact issue.
Smith put that to South Auckland Motors which said this was wear and tear, and the vehicle was out of warranty, but it would offer to chip in $3000 as a goodwill gesture.
Smith felt the dealer could do more.
"Anyone who buys a car doesn't expect the car to blow up so soon," she told Fair Go.
Petrol in the diesel?
South Auckland Motors then asked to see the truck, a month after the breakdown. It quickly reached a different verdict.
"The diagnostic work our factory trained, experienced technicians carried out utilised the specialist equipment we have on site that can analyse all aspects of Lizzy’s vehicle," says Mike Tappenden, dealer principal at South Auckland Motors.
"Our technicians were able to definitively determine that the breakdown was in fact due to the failure of the high-pressure fuel pump and multiple injectors. Our technicians concluded that fuel contamination was the cause of the failure."
Smith had kept receipts for her last two fills at diesel pumps.
"It just didn't make sense, given that the last fill was in Whangārei. I'm no fuel expert here, but I would think if you put a whole tank of the wrong petrol in your car it would not make it back to Auckland."
Smith wanted proof. The workshop said it had a fuel sample she could inspect. She asked for a contamination test and the workshop used a reputable lab to run a boiling point test - a standard measure of what's in fuel.
The result showed a slightly lower boiling point. The report stated that opinions and interpretations are outside the scope of the laboratory's accreditation; nonetheless it provided an explanatory comment in an email that says there could be up to 1.5% of lighter hydrocarbons other than diesel present in the sample.
Could is the word.
The email that Lizzy received from the workshop said the test result confirms there's up to 1.5% lighter hydrocarbons present, confirming its theory of contamination as the cause.
Checking the science
Fair Go showed the result to University of Canterbury's Professor Richard Hartshorn, who had no problem with the lab or its methods for testing diesel and petrol, only with the conclusions drawn.
"From the chemistry point of view with the test results that you showed me, I could not say that there was contamination," he said.
Hartshorn explained that petrol and diesel molecules are very similar complex mixtures with a range of boiling points; for petrol and diesel that range will often overlap, depending on the samples taken, which might explain why diesel could still show that result, but confirm nothing.
"The bottom line is those results are not a smoking gun in any way shape or form," Hartshorn told Fair Go.
Fair Go checked with the government authority that measures what is fit for sale, giving it a copy of that test result which the workshop claimed was proof of contaminated diesel.
“The report is consistent with data we would expect to see for diesel. In particular, the data for distillation is typical for automotive diesel sold at service stations across the country, including the figure of initial boiling point,” said Stephen O’Brien, national manager at Trading Standards.
Fair Go also talked to Gull about where Lizzy had filled up a week before the breakdown.
"Gull has double-checked all processes and events at both Gull Kaitaia and Gull Whangārei and found nothing out of the ordinary has occurred that could contribute to a motor vehicle issue," said Mike Williamson, Gull New Zealand's retail business manager.
South Auckland Motors still insisted that somehow, petrol had caused the damage to the diesel fuel system of Lizzy's Ford Ranger, but faced with those findings, it had a rethink.
"We accept the position that the testing was inconclusive with respect to the contamination levels required to cause the damage to the vehicle’s fuel systems. We are continuing to undertake further investigation on the failed components, both to satisfy our own curiosity and to ensure we fully understand what has occurred to Lizzy’s vehicle," Tappenden said.
"Putting aside the multitude of technical and other details and our various positions, we agreed to extend our gesture of goodwill and we have completed the repair at our cost."
Lizzy is elated that the truck is back on the road and thrilled she has no bill to pay; she too is still mystified by what has happened, but happy persistence paid off.
For her that's the real lesson if you think you're right:
"Stick at it, keep going."
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