Bahrain F1 test: Nico Rosberg still has Mercedes reliability fears

Mercedes has generally led the way in terms of mileage and laptime so far, but the W05 has suffered several niggling reliability issues along the way.

The team undertook what it described as a "precautionary" engine change before Saturday's test at the Sakhir circuit, which delayed Rosberg's final day of running, and then missed the first three hours on Sunday due to gearbox issues.

Rosberg went on to clock more than 100 laps and set the second fastest time of the test on Saturday, but the three-time grand prix winner feels Mercedes still has some bugs to iron out before the first race in Melbourne.

"We've had some good tests but reliability is still a concern for us as it is for everybody else," said Rosberg. "It's tough to get the car 100 per cent ready.

"We might be in a better position than some other teams but we need to get to the end of the race so that's a big challenge."

The German was satisfied with his last day of testing overall, despite some weather issues and his loss of track time.

"Conditions were tough out there with a sandstorm and really strong winds, which made it difficult to learn a lot, but it was still a good day," said Rosberg.