A San Fernando Valley gas station may be costing drivers a lot more than $4 a gallon with a watered-down product.

A Valero station in Chatsworth has discovered a bad mix of gasoline in its pumps that could cause expensive damage to customers’ cars.

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One family told KCAL 9’s Juan Fernandez the problem began immediately after filling up at the station at De Soto and Nordhoff.

“I drove less than a mile down De Soto and my car stopped working,” said Joni Merida. “I pressed on the gas, it wouldn’t go, I knew I was having a problem.”

Merida took her 2009 Corolla to the dealership and found out what was causing the problem.

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“They gave us a call and told us, ‘There is water in your gas’,” she said. “So I knew right away it’s the Valero gas station that I went to.”

The Merida family is now driving a rental car while their vehicle is being repaired.

Jeff, the manager at the station, said a shipment of gas that came in earlier Wednesday had higher-than-normal concentrations of ethanol the corn-based biofuel used as a clean-burning additive to gas.

Studies show that at excessive levels, ethanol can cause engines to run improperly and damage rubber hoses, gaskets and engine parts.

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Valero officials said ethanol lowers the octane level of the gas, and have offered an octane booster for all customers who filled up at the station on Wednesday.