Championship leader Lewis Hamilton maintained his supremacy in Friday’s second free practice session for this weekend’s United States Grand Prix when he outpaced his Mercedes team-mate Nico Rosberg by just 0.003 of a second.
But he finished his day back in the pits as his team worked on his car to deal with an unspecified leak that raised reliability alarms as he pursues his fifth straight win.
Hamilton had also been fastest in the morning session and his afternoon supremacy meant that he had now been fastest in 14 of the 17 second free practice sessions this year.
The two Mercedes men, separated by just 17 points in the title race, were more than a second clear of third-placed man, two-time champion Fernando Alonso of Ferrari.
“The team just said to me ‘you’ve got to stop, there’s something wrong with the car. But I don’t think it particularly affects the weekend.
“They pulled the floor off and there was some kind of fluid, some kind of leak. I had to stop just in case. The gearbox was working fine and the race box goes in tomorrow and I am confident that will be fine.”
Rosberg admitted he felt concerned by Hamilton’s car issue.
“Of course, it’s worrying for me to see that his car broke down. We need to see what it is and get on top of it and hopefully it doesn’t impact the race weekend.
“I have full confidence in the team but it’s not ideal, it shows our car is not 100 per cent robust.”
He added that he felt confident of matching Hamilton’s pace in qualifying on Saturday.
“It’s tight as usual, three thousandths, but I have them in my pocket. I know where they are so no worries. I’m going to pull them out tomorrow.”
He said he had one worrying moment when he knocked his clutch pedal accidentally – due to an itch.
“Can you imagine of all the things that can happen? I lifted my leg and hit the clutch pedal because I got an itch.”