Mark Webber declined to express a view about the prospects for his new Red Bull RB7 after only completing 17 laps concentrating on basic checks on his first day in the car.
The Australian was due to complete half a day after taking over from World Champion teammate Sebastian Vettel in the afternoon, but a master cylinder problem allowed him to run only during the final hour.
"I had a very short run of only 40 minutes or so," said Webber when asked by AUTOSPORT for his impressions of the car. "We did pretty basic data gathering because we knew that we were running short of time.
"When you have such a small window, you can't really get your teeth into too much quality stuff so we decided to do the more mundane stuff. At every test you have to do stuff like that, but there was a window to do it there and we'll get on with it tomorrow."
It was also Webber's first taste of the new Pirelli tires, as the Australian sat out last November two-day test in Abu Dhabi. Despite completing few laps, he echoed rivals' reaction to the tire, which has generally been to point to the increased degradation and rapid loss of lap time after several fast initial laps.
"The same as what everyone else has been saying," said Webber of the tires. "They behave a bit differently, but I will have a better understanding tomorrow once I get into proper running and get down to the pace of the car."
Webber also confirmed that he was comfortable in the cockpit of the RB7.