Formula One World Championship runner-up Lewis Hamilton gave McLaren's 2008 car his seal of approval after trying it out for the first time in Jerez on Thursday.
The 23-year-old Briton Lewis Hamilton completed 103 laps at the Jerez circuit while new team mate Heikki Kovalainen of Finland did 101.
"I saw the completed car for the first time on Monday at the team's launch in Stuttgart and I have been pretty impatient since then," said Hamilton in a team statement.
"My first impressions are encouraging. I covered over 103 laps, which is 456kms, today. Considering this is only the second day the car has been on track, I am pretty happy with that.
"We have a lot of work to do, but now we have a real understanding of where we are starting from."
Hamilton, who lost the title by a single point to Ferrari's Kimi Raikkonen in his rookie season last year, will continue testing with Kovalainen on Friday and next week.