Kimi Raikkonen was left to rue a loss of track time after completing only four installation laps during the morning session of the third day of testing in Spain.
Ferrari team-mate Sebastian Vettel topped the first two days of running but the outfit was forced to conduct extensive fuel system checks in the morning, restricting Raikkonen's time in the SF16-H.
Raikkonen was ultimately able to rack up 74 laps during the afternoon session and finished the day in third position.
"The atmosphere in the team is quite nice even if, honestly, we're still working on different things and still find something new to work on, but I am sure it's going to be a better car than last year's," he said.
"There are always small changes between one car and another, they are never the same. We had improvements in many areas from the past season.
"These are early days, especially for me with this car. We are happy so far, even if we know that there are still a lot of things to do.
"There were tricky things and it takes time to fix them. It was painful losing time today, but we always try to do our best. There are always mistakes but we always want to improve and learn from them."