Kimi Raikkonen put Ferrari back on top in Formula One's preseason testing on Thursday, while Mclaren struggled with reliability issues for the second straight day.
The Finnish driver led the morning session at the Circuit de Barcelona, ahead of Kevin Magnussen of Renault and Max Verstappen of Toro Rosso. lewis Hamilton was sixth in his Mercedes after completing 99 laps, the most of any driver.
Raikkonen's teammate Sebastian Vettel was fastest in the first two days of testing and Nico Hulkenberg led the way on Wednesday for Force India. Vettel's time of 1 minute 22.810 seconds on Pirelli's new ultra-soft tyres has been the fastest of the week so far.
Two-time champion Fernando Alonso was held to only three laps on Thursday because of an apparent water pressure issue on his Mclaren. The Spanish driver was not able to set a time. Teammate Jenson Button had completed only 51 laps on Tuesday, the least among the 11 drivers who tested, because of a hydraulic leak.
Mclaren was plagued by reliability problems throughout last season under a renewed partnership with engine supplier Honda, but it had showed significant signs of improvement in the first two days of testing in Barcelona.
Daniil Kvyat was fourth with Red Bull and Felipe Nasr fifth with Sauber, which is yet to debut its new car.
Indonesian rookie Rio Haryanto completed only 26 laps with Manor, seven more than Mexican driver Esteban Gutierrez with newcomer Haas.
The cars will return to the track for the final time this week in the afternoon session. Teams will test for the last time March 1-4, again in Barcelona. The first race is March 20 in Australia.
Hamilton lashes out
Defending Formula One world champion lewis Hamilton has hit out at plans for a revolution in the sport's regulations in 2017 and claimed drivers' opinions should be more valued.
Changes to the regulations hope to add more speed to the cars in a bid to liven up the sport after Hamilton romped to the title in the dominant Mercedes for the past two years. However, he claimed the change to heavier hybrid cars in recent years is the real problem with the sport rather than the lack of competition.
"I don't think the regulations are fine, even if there were five teams battling at the front of the grid, but I like a different kind of car," said the Englishman.
The deadline on when agreement must be reached for changes to be implemented for the 2017 season was pushed back to April 30 by a meeting of the F1 strategy group and commission on Tuesday.
However, a new knockout format for qualifying will be introduced ahead of the start of this season on March 20 to try and mix up the grid to provide for more exciting races. "I just realised that when I got to Formula One I think the car was 600 kilos and now it's 100 kilos heavier, that is the big difference," added Hamilton.
"We don't actually have to change the regulations much to go three seconds faster, just make the cars lighter. They are just super heavy. It is ridiculous if they are going to be even heavier. They were great at 600 kilos, nice and nimble, easier for the tyres too as there were fewer tyre blowouts.
"The heavier the car, there is more force on the tyres, so the tyres feel worse."
And Hamilton believes more consultation, especially with experienced drivers who have had to deal with the shifting sands of F1's technical regulations over the past decade, would produce better solutions than those being offered at present.
"I think the drivers should be consulted. We have feelings about the car, we know what would be better and what is not good for the car, especially the drivers who have been driving for 10-15 years through all the changes and know which ones work and don't work.