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DENVER — At least one vehicle is in the shop after a serious fuel mix-up at a Denver gas station.

According to state inspectors, a fuel distributor accidentally poured regular gasoline into the diesel tanks on Saturday at the Phillips 66 Conoco station at 3895 Peoria St. in Denver.

Nobody caught the mistake until a customer who filled up there Sunday reported mechanical issues with his diesel truck.

“It looks like there was around 500 gallons of gasoline dropped into that tank,” said Scott Simmons with the Colorado Department of Labor and Employment’s Division of Oil and Public Safety.

State fuel inspectors took samples from the gas station’s pumps Tuesday morning. Chemists performed flash point and distillation tests on the samples and discovered the fuel was heavily contaminated with gasoline.

“I’m going to say there was probably a relatively low percentage of actual diesel fuel in there for the low flash point that we’re seeing in our analysis, as well as the smell of gasoline in that sample,” Simmons said.

It is unclear how many gallons of the tainted diesel was sold to customer between Saturday and Tuesday morning. Only one person has come forward claiming mechanical issues, and there could still be several more.

“Diesel is a compression ignition product and so there are no spark plugs,” Simmons said. “What happens is that gasoline is a lower flash point and so it fires sooner. It takes less compression to fire, which will throw the timing off on that engine and cause some serious drivability issues and may cause extensive damage.”

Not everyone who purchased fuel from the Phillips 66 diesel tanks over the weekend will be affected.

Experts say some older diesel engines handle gasoline better than newer models. Some customers also might only have topped off their tanks, which would minimize the effect of the gasoline.

Fuel mix-ups are fairly rare. Oil and Public Safety inspectors said they only see roughly two to three cases per year statewide.

According to the owners of the station, this is the first time they have been given the wrong product.

“The underground storage tanks are clearly marked,” Simmons said. “So really it’s a driver error. I just think it was a lapse of concentration there that caused this.”

The gas station owners and fuel distributor are covering the cost of repairs for the driver who reported the mistake.

The station flushed its fuel lines Tuesday. State inspectors will be back Wednesday to test the pumps and if they show uncontaminated diesel fuel, the gas station will be able to turn the diesel pumps back on.