McLaren was the least reliable team of the 2011 pre-season.
"I'm not going to lie. It's not the best way to go into the season," admitted Jenson Button.
The MP4-26 was launched late after skipping the opening Valencia test, but it has since been plagued with exhaust, hydraulic and aerodynamic problems.
Button insisted: "We are a long way down on it (mileage) but there is no point getting negative about it and down at this point of the season."
Third best was Sauber, ahead of Mercedes, Toro Rosso, Renault and Williams.