Formula One champion Lewis Hamilton gave his new McLaren the seal of approval yesterday after getting back behind the wheel for the first time since he won the title last November.
However the 24-year-old Briton, who completed 81 laps in the MP4-24 at the Algarve circuit in southern Portugal, warned that his team had their work cut out ahead of the season-opener on 29 March.
"It was good to be back working with the team, it felt like I'd hardly been away because it was easy to slip back into the routine," he said.
"It's amazing to think that, while I've been to Woking throughout the winter, I haven't properly driven a Formula One car since the Brazilian Grand Prix two months ago, but everything very quickly felt normal today."
Hamilton suffered an early setback before lunch when the car halted out on the damp track and had to be brought back on a truck.
The team said the car had experienced a "precautionary engine systems shutdown" which was rectified without having to change the engine. Hamilton returned to the track in the afternoon and set the second fastest time of the 2009 specification cars.
"This first test was all about just getting used to the new car and the new regulations and about giving my feedback to the engineers," he said. "It wasn't about setting a fast time.
"The car feels good, we've made lots of progress over the winter and I'm looking forward to developing the car ahead of the Australian Grand Prix.
"It's going to be an extremely busy winter. I've only been in the car for one day and our usual job list for the weeks ahead is already enormous," he added.
Meanwhile, Hamilton's former team mate and double world champion Fernando Alonso did 86 laps in the new Renault but was slowest of the five drivers.
"There are so many things to learn in a short time and we need to maximise our time on track, so to do so many laps today was a good effort," said Alonso.
Germany's Nico Rosberg, in a Williams, was the quickest of those in the new cars behind 20-year-old Swiss rookie Sebastien Buemi in the 2008 Toro Rosso.
Williams technical director Sam Michael said the Toyota-powered FW31 had enjoyed good reliability, completing more than 670 km on its third day on the track.
Timo Glock's first outing in the new Toyota TF109 suffered a setback when an oil pipe became disconnected and set the car on fire.
"My first impression of the new car is good," said the German. "I am happy with it. In the morning, on a wet track, I felt pretty comfortable and it was easy to drive."
Poland's Robert Kubica had an untroubled day testing the new BMW-Sauber in Valencia, eastern Spain, while Brazilian Felipe Massa completed 104 laps for champions Ferrari at the Mugello circuit in Italy.