Jenson Button hailed a positive first day with the MP4-31 and noted the vast improvements made regarding the energy deployment available from the Honda engine.
McLaren was plagued by a lack of performance and reliability in 2015 but the Briton was able to complete 84 laps on the opening day of pre-season testing in Spain.
A late lap of 1:26.735 on the Soft tyres enabled Button to finish sixth in the standings.
"Today has been all about system checks and trying new things – there are lots of differences with this car, and with the engine," he said.
"The stand-out thing that’s been very positive today is the deployment: it’s been very consistent throughout the day, we had no issues, and it was quite a bit better on long runs than last year. This is good, because it allows us to see other weaknesses in the car that we still need to improve.
"Overall, a good day actually and I’m reasonably happy. In terms of outright pace, who knows? We’re not going out there to set a lap-time, we’re focussing on checks and having the engineers talk to me, as there’s so many different electronic things that we’re trying out, which is very interesting.”
"We completed five more laps today than we did in the first four days of testing last year, which is definitely an improvement! As long as we can see improvements, and the feeling of the car is good, it’s something to build on."