Red Bull pack up early, Massa fastest
Reigning double Formula One world champions Red Bull rounded off a terrible opening week of pre-season testing as they ended the fourth and final day in Jerez having completed a total of just 21 laps.
Williams' Felipe Massa was fastest on Friday with a lap of 1min 29.023 mins as the teams powered by Mercedes engines continued to make a strong start.
Ferrari's Fernando Alonso was second after logging a mammoth 114 laps, while Force India's test driver Daniel Juncadella was third.
The headline story of the day, though, was once again the disappointing showing by Red Bull as for the third day in a row they decided against running in the afternoon.
Aussie Daniel Ricciardo had managed to get seven laps out of the RB10 early in the morning, but his best time was over 16 seconds slower than Massa's.
"It's such a complex system this year that it is not going to take 24 hours to solve. It is best now to get some time away from the track and figure out what needs to be done," said Ricciardo.
Team principal Christian Horner accepted it had been a far from glorious start for a team that has won the last four drivers' and constructors' world titles.
And the race is now on for Horner and chief technical officer Adrian Newey to come up with a solution before the next series of testing in Bahrain which begins on February 19.
"It's been a very difficult test," he said in a statement released by the team.
"We have had numerous Renault issues as well as chassis cooling issues, which have affected our progress. However, despite the lack of mileage, what we have managed to learn shows that the problems should be solvable for the next test in Bahrain.
"Part of the purpose of this early test was to learn about any issues ahead of the start of the season and there will now be a lot of focus on the dyno over the next few weeks."
There will be eight days of testing in all in two four-day blocks in Bahrain before the season gets under way for real at the Australian Grand Prix on March 16.
Once again the winners were the teams with Mercedes-powered engines on Friday as Massa raised hopes that Williams could be more competitive this season after a disappointing 2013 season.
The Mercedes duo of Nico Rosberg and Lewis Hamilton also combined 132 laps after Hamilton took over from the German in the afternoon to even out their lap count for the week.
And Hamilton hailed his team's start as they look to improve on their second place finish in the constructors' championship last season.
"It's been a fantastic week. We've managed to do a lot of laps," said the Englishman.
"It's too early to make judgments, but right now my car feels really good. It is a new challenge and I'm really enjoying it."
However, neither Rosberg or Hamilton could better the time set by Danish rookie Kevin Magnussen as he finished fourth fastest.
Magnussen made a spectacular start to his McLaren career by going fastest on his first outing on Thursday and he completed 110 laps before spinning off the track towards the end of the day.
The problems at Red Bull have been reflected across all the teams using Renault engines as both Toro Rosso and Caterham have also struggled this week.
Japanese driver Kamui Kobyashi did manage 54 laps in the Caterham, but his time of 1min 43.193 only bettered fellow Renault-powered drivers Ricciardo and Toro Rosso's Daniil Kvyat.