With Nico Rosberg completing over 150 laps on Sunday, Hamilton looked set to follow suit after accumulating more than 90 laps early on day two at Jerez. However, Hamilton stopped at the end of the pit lane with what proved to be a water leak from a component failure which ended his running, and with a number of reliability issues in 2014 he said it is an area Mercedes needs to improve.
"We focus on all things, but of course reliability would massively help, and it's an area last year we could have done better,” Hamilton said. "We were about 80 per cent reliable, whereas we want to be 90 to 95 per cent, so that's something we are working on, and of course we want to be faster.”
However, having been able to get in so much mileage before the problem, Hamilton said he had noticed an improvement with the car.
"Feels pretty much the same, feels like we've got more downforce, so I think we have taken a step. How big? I can't say. We weren't out there trying to do fast lap times. It's good we've had such good running over the first two days, good reliability. But we will continue to work on that which is the foundation we want to improve on.
"As for the water leak, I can't tell you too much about it. The team will work on it overnight and the car will be fine for tomorrow."
Click here for the gallery of the second day of testing at Jerez