Feb 8 Lewis Hamilton made up for lost time by doing 145 laps of the Jerez test circuit on Friday with Mercedes team principal Ross Brawn hailing the 2008 Formula One champion for his work in driving the team forward.
The 28-year-old former McLaren driver did only 15 laps before a brake failure sent him crashing out on his test debut with his new team on Wednesday but returned for a full day's work.
His efforts were interrupted only when testing was halted for nearly an hour to enable workers to repair a damaged kerb and fill a hole between turns 10 and 11 with quick-drying cement.
Hamilton told reporters that Mercedes, largely uncompetitive last season, were where he hoped they would be in terms of performance and he was giving them plenty of feedback.
"We have some work to do but it doesn't feel like it was a disaster," he said. "I feel like it's a good platform, a good foundation to work from.
"Definitely we are going to keep asking for downforce and hope the guys continue to do a great job at the factory," he added.
Brawn welcomed any constructive criticism from Hamilton and his German team mate Nico Rosberg, who did 148 laps on Thursday.
"I think we've made it very clear to Lewis that he's part of the solution," the Englishman told reporters. "He's part of the solution to get us where we want to be and he knows that and understands it and I think he's relishing it.
"He gives us reference points and helps us understand what we need to focus on... I welcome that approach. It needs to be constructive and it needs to be positive criticism of the right sort and that's always helpful for the team to drive it forward."
Hamilton ended the final day of the test with the sixth fastest time of one minute 18.905 seconds.
Kimi Raikkonen, the 2007 champion, was quickest for Lotus in 1:18.148 with Frenchman Jules Bianchi setting out his credentials for the Force India drive with the second best lap of 1:18.175.
Force India have yet to say who will partner Britain's Paul Di Resta this season, with Ferrari academy driver Bianchi a frontrunner.
Red Bull's triple world champion Sebastian Vettel was third fastest after doing 96 laps.
Spaniard Pedro de la Rosa took over in the Ferrari for the final day of the first pre-season test but the test driver's running was limited by a fiery oil leak early in the session. The team blamed a gearbox fault.
Ferrari still ended up with the fastest lap of the week, the time of 1:17.879 set by Brazilian Felipe Massa on Thursday.
The second pre-season test starts in Barcelona on Feb. 19 with Spain's double world champion Fernando Alonso having his first drive in the new Ferrari 138 after skipping Jerez and Williams presenting their new car. (Reporting by Alan Baldwin, editing by Toby Davis)