Fernando Alonso had completed just three untimed laps in the morning session when his MP4-31 was consigned to the garage, but despite McLaren’s best efforts they were unable to get the Honda-powered machine back out on track.
“Unfortunately, the coolant leak we experienced on the car today was in a tricky position, which meant it took longer than usual to locate and fix," explained Director of Engineering Matt Morris.
"It’s always frustrating when a small issue hampers your running for much of a day, but thankfully it’s relatively minor and we can now look to preparing the car for the second test on Tuesday. Testing is testing, and it gives us the opportunity to identify and work on reliability issues before we start the season.
“Over the course of the first four days in Barcelona we’ve done a good amount of running and already learned a lot about our package, which should stand us in good stead for next week. We’re definitely ahead of where we were last year in terms of system checks and integration, so at the second test we’ll be able to focus more on race simulations and setup, as well as characterising our package’s performance.”
Alonso agreed that the setback was not the end of the world for the team: "Overall, we’ve managed a good number of laps during this test, which means we have a lot of data to analyse and learn from," the Spaniard said. "Over the weekend we’ll work hard to get everything prepared for next week, with the aim of getting as much time on track as possible [at the second test].”
In three previous days of testing McLaren had completed some 257 laps - a significant improvement on 2015 when they managed just 79 laps at the opening test.
Alonso has already stated that McLaren are targeting having the best chassis on the grid by the first European races of the season.