McLaren have defended their "ambitious" car design after Fernando Alonso suffered more reliability problems on the final day of Formula One pre-season testing.
The Spaniard was sidelined for almost five hours by an oil leak and engine change before eventually returning to put in the second fastest lap of the day and third fastest of this year's testing.
Australia's Red Bull driver Daniel Ricciardo was fourth quickest on the slower "supersoft" tyre, just behind Renault's Carlos Sainz.
McLaren have lost time to a variety of problems, starting with a wheel nut issue that sent Alonso spinning into the gravel after just six laps of the very first day of testing in Barcelona.
On Tuesday Belgian Stoffel Vandoorne was twice stopped by battery and hydraulic failures while Alonso lost about seven hours after an oil leak forced another engine change on Wednesday.
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"We have an ambitious design around the car and you can see that the car is a little bit different from the other Renault-engined cars," racing director Eric Boullier said.
"We have not lost our capability of designing fast cars and I hope you will see it on track soon. We have to be ambitious, and to be ambitious you have to take risks."
Kimi Raikkonen set the fastest pace on the final session. His lap of one minute, 17.221 seconds came within 0.039 seconds of the unofficial track record set by Ferrari teammate Sebastian Vettel the previous day.
Defending champion Lewis Hamilton and Mercedes teammate Valtteri Bottas focused on running race simulations for a second straight day.
Mercedes ended preseason testing with a total of 1037 laps, the most of any team.
The season opens with the Australian Grand Prix in Melbourne on March 25.
