Barcelona - Kimi Raikkonen continued Ferrari's positive start to the 2016 Formula One season with the fastest time on the fourth day of pre-season testing as the McLaren-Honda partnership endured another day to forget.
Ferrari have now topped the timesheets on three of the opening four days of testing.
Raikkonen recorded the third fastest time of the week of 1min 23.477 on the new ultrasoft tyres, but was over six tenths of a second down on the time set by teammate Sebastian Vettel on the same setup on Tuesday.
McLaren-Honda's hopes for a fresh start to the 2016 season came to a crashing halt as Fernando Alonso failed to register a single lap time all day.
The two-time world champion managed just three installation laps before lunch before the team ruled out anymore running for the day due to a coolant leak.
McLaren-Honda's renewed partnership proved to be a disaster last season as continuous reliability problems and a lack of performance from the Honda engine left them ninth out of 10 teams in the constructors' championship.
Most of those problems appeared to have been alleviated as Jenson Button and Alonso logged over 200 laps in the first two days of testing after what racing director Eric Boullier described as a complete revision of the car.
However, Button's second day in the car on Wednesday was cut short due to a hydraulic problem.
And the fans in Barcelona were left disappointed as local hero Alonso was stuck in the garage all day on Thursday.
The Woking-based team now have a huge amount of ground to make up at the second four-day test at the same Circuit de Catalunya track from March 1-4 with the opening race of the season in Australia less than a month away on March 20.
Russian Daniil Kyvat was second fastest for Red Bull, albeit nearly a second back on Raikkonen as most teams prioritised reliability over speed.
However, Force India's impressive start also continued as test driver Alfonso Celia was third fastest after Nico Hulkenberg recorded Wednesday's best time.
A former McLaren man Kevin Magnussen enjoyed a much more encouraging day for Renault on their return to the sport as a constructor with 153 laps and the fourth fastest time.
Mercedes again piled on the laps as world champion Lewis Hamilton racked up 99 before handing over driving duties to Nico Rosberg for the afternoon down in sixth fastest.
Rosberg added 86 more to take Mercedes' tally for the opening four days to 675.
The German giants also caused a stir by debuting a new nose to the W07 which could give the runaway leaders in the past two drivers' and constructors' championships an even more commanding advantage in 2016.