$ 0 0 Mercedes' early season strength was again evident with German Nico Rosberg going fastest in Friday's secondpractice for the Malaysian Grand Prix as a number of Formula One teams suffered teething problems on a tricky day. Rosberg, who won the season opening race in Australia two weeks ago, clocked a best time of one minute, 39.909 seconds in the second session at a steamy, slippy Sepang circuit, where track temperatures reached 50 degrees Celsius, testing the cooling systems on the new V6 turbo engines to the max. Rosberg's teammate Lewis Hamilton had clocked the best time of 1:40.691 in the opening session despite sliding off the track earlier on Friday, but the Briton was only fourth in the second with a 1:40.051 after more grip issues. The 2008 world champion complained on the team radio after his first venture into the gravel that the circuit was "like driving on marbles" with less downforce and more torque and power on the new cars taking some getting used to. Kimi Raikkonen was secondquickest on Friday for Ferrari with a best time just 0.035 seconds back of Rosberg, with team mate Fernando Alonso fifth with a 1:40.103. The Spanish double world champion had led the timesheets in the opening half of the first session before making an error and spinning at turn eight and then concentrated on system and balance checks as his times slipped back.