Bahrain Test 2, Day 4: Problems galore for F1's big guns as Mercedes end winter on top

Lewis Hamilton ensured 2014 title favourites Mercedes ended their impressive winter's work on top of the timesheet as F1's most challenging and unpredictable testing season in recent memory came to a problem-filled but dramatic conclusion in Bahrain.

Mercedes, meanwhile, had already lost the majority of the first four hours of running after a gearbox glitch had to be rectified even before Hamilton completed an installation lap. Such was the unreliability-filled nature of the final day, that even the previously impregnable Williams FW36 ground to a halt for the first time this winter, the team citing a high-mileage failure of their internal combustion engine. Nevertheless, that late stoppage couldn't mask what has proved a highly promising winter for the apparently revitalised Williams team as Valtteri Bottas again topped a century of laps and finished with the second-fastest time on the Day Four timesheet, a 1:33.987. From a quietly efficient start to life with their new Mercedes-powered FW36 back at Jerez in late January, Williams' fastest overall time in Bahrain means they have emerged as more than dark horses for the Melbourne season-opener with the FW36 displaying both impressive pace and, perhaps most crucially of all, reliability. Ferrari broke the Mercedes-powered hegemony at the head of the timesheet with Fernando Alonso, despite an afternoon stoppage of his own, clocking the Scuderia's fastest time of the test on 1:34.280 to take third place. That late improvement placed him ahead of Force India's Nico Hulkenberg - another red-flag culprit - and Toro Rosso's Jean-Eric Vergne. Sauber, meanwhile, achieved a mileage record for this winter by clocking an astonishing single-day total of 177 laps - 40 laps more than the previous benchmark - as they split their final-day schedule between Adrian Sutil and Esteban Gutierrez. The two Sauber drivers were split on the timesheet by Marussia's Max Chilton, whose 1:36.835 was a test best for the Banbury team and over one second quicker than perennial rivals Caterham managed all week. They also ended what had been difficult week with a race simulation.