Hamilton fastest in Bahrain
Lewis Hamilton brought the curtain down on pre-season testing with the quickest time of the final day, but it was not without issues.
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Hamilton spent almost the first four hours of the day at the Sakhir circuit in Bahrain in the garage as his Mercedes mechanics worked on a gearbox problem.
Once on track Hamilton completed 69 laps, with his best a one minute 33.278secs, 0.020secs behind Felipe Massa's benchmark for Williams on Saturday.
The gearbox trouble, however, in conjunction with a number of other niggles for Mercedes throughout the final test, will give the team more cause for concern than Hamilton's lap will give encouragement.
With the season-opening Australian Grand Prix just a fortnight away, Mercedes and virtually every other team in the paddock will head off Down Under with trepidation.
The regulations that centre around the new 1.6-litre V6 turbo-charged hybrid power units have caused every marque an array of problems, none more so than Red Bull.
After failing to complete a lap on Saturday, front-end technical woes caused problems on Sunday for Sebastian Vettel who stopped on track.
Although 77 laps were eventually completed - the most by Red Bull on one day this pre-season - the majority of those were at low speed.
Vettel eventually dipped down into the one minute 37secs late on, but even then that was just over four seconds adrift of Hamilton.
The reigning four-time world champion knows the start to the campaign could be a tough, troubled affair.
"We're concerned about our lap times, it's not a secret," said Vettel.
"We cannot do the times the guys at the top are doing for a couple of reasons, but at the moment we have bigger problems to solve than just the pace.
"We haven't done enough laps, the speed is not there compared to some other teams so we have to wait and see what happens when we get to Australia.
"But surely things will calm down. We have to use the two weeks that we have until then to fit new parts to the car and build it to the best knowledge that we currently have."
It was a final session that was extended by 25 minutes due to the fact there were eight red flags, with one of those unfurled during the extended period.
To accommodate, circuit officials were forced to turn on the lights as twilight set in, and which will be used extensively for the race in early April given it will be a night event for the first time.
Behind Hamilton, WIlliams again fared well as Valtteri Bottas chalked up a day-high 108 laps, the Finn seven tenths of a second behind the Briton.
In the combined hands of Adrian Sutil and Esteban Gutierrez, Sauber accumulated a remarkable 177 laps on the day, making amends for the solitary lap managed by the former on Saturday, with the duo sixth and eighth on the timesheet.
Ferrari's Fernando Alonso, Nico Hulkenberg for Force India and Toro Rosso's Jean-Eric Vergne remarkably all completed 74 laps to finish third, fourth and fifth quickest, albeit with 1.4secs separating them.
Marussia's Max Chilton finally got same laps on the board, with the Briton leapfrogging up to seventh in the closing stages, 3.5secs off of Hamilton.
Behind Gutierrez was Vettel, with McLaren's Jenson Button ninth, but with his final two days in the car proving to be miserable and frustrating.
After a gearbox issue on Friday curtailed Button's running to 52 laps, the 34-year-old's final outing resulted in only 21 due to an engine failure on a high-mileage unit.
Kamui Kobayashi amassed 106 laps for Caterham, but was five seconds down, with Lotus' Romain Grosjean bringing up the rear as a fire brought his day to a premature end after 32 laps.