MONTMELO, Spain (AP) McLaren's misery mounted after another malfunction left Jenson Button stranded as Felipe Massa steered Williams to the fastest lap during Formula One preseason testing on Thursday.
A hydraulic leak that McLaren said will require it to change its new Honda engine limited Button to a session-low seven laps, and the slowest lap time at almost eight seconds behind Massa.
McLaren's latest setback came four days after Fernando Alonso ended up in the hospital following a crash, ruling the Spaniard out of the final tests, less than three weeks before the season-opening Australian Grand Prix.
''We have an engine problem now. I am not sure how it will unfold over the next four days,'' McLaren chairman Ron Dennis said. ''We are still at the foot of a steep mountain.''
Massa clocked the fastest lap through five combined days of running at the Barcelona-Catalunya Circuit.
''It was a good day for us and the car behaved well,'' Massa said. ''I have just one more day in the car before the first race, so Saturday will be important.''
Defending champion Lewis Hamilton also had trouble, and got in only half a shift due to problems with his Mercedes.
McLaren is suffering from a lack of both speed and reliability after its switch from engines made by Mercedes to Honda. A faulty seal on its engine had already plagued Button at the second test here last week.
Overall, McLaren has registered the fewest laps of any team this preseason with just 210.
Compare that to champion Mercedes, which in two days at the first test in Jerez recorded more laps than McLaren's current total. Mercedes, despite its own glitch on Thursday, has racked up 944 laps so far.
Button will try again on Friday after the team changed its schedule that initially had reserve driver Kevin Magnussen driving in place of Alonso.
Sauber's hopeful preseason continued with Marcus Ericsson managing to edge Hamilton with a late run for the second fastest lap - 0.776 seconds behind Massa. He was also the day's busiest driver with 122 laps.
''It was a productive day and, for me, the best one of the preseason so far,'' Ericsson said.
Hamilton set the pace early and got in 48 laps, but never emerged after the lunch break. Massa then went to the top of the timesheet and set to shaving his own mark in another promising ride for Williams.
''Sometimes you have those days. I don't see it as too much of a negative,'' Hamilton said. ''It's good that you find these things, whatever issues you might have, and iron them out now. It means, hopefully, you won't find them at the first race.''
Daniil Kyvat of Red Bull, Romain Grosjean of Lotus, and Kimi Raikkonen for Ferrari came with the fourth, fifth, and sixth-best times, all over two seconds off Massa's pace.
Toro Rosso's Carlos Sainz Jr. was ahead of Button at the bottom.
Force India said its car for the new season is finally ready and is on its way to Spain. It expects Nico Hulkenberg to give it its first spin on Friday afternoon in a rushed attempt to break the new vehicle in for the Australia GP from March 13-15.