Ferrari's Kimi Raikkonen set the fastest lap in the final morning session of the first test at the Circuit de Catalunya.
Tyre supplier Pirelli had requested that Day Four was set aside for wet weather testing but, as the track began to dry out, teams were gradually able to revert to softer tyres.
Raikkonen set a time of 1:22.305 on soft tyres, with Red Bull's Max Verstappen rising up to P4 as lunch hour approached with a 1:23.920.
Sandwiched in between was Haas' Romain Grosjean, who went on a late run on supersofts and posted a best time of 1:22.739, and McLaren's Stoffel Vandoorne (1:23.918) in P3.
Mercedes and Lewis Hamilton were notable absentees throughout the morning, as the W08 stayed in the garage whilst mechanics worked on an electrical fault.
They did emerge, though, for a nine-lap stint in the final hour with Valtteri Bottas starting his day's work a little earlier than expected.
A rumble of life… ????
— Mercedes-AMG F1 (@MercedesAMGF1) March 2, 2017
However, Williams will miss the day entirely after Lance Stroll's crash on Wednesday meant the FW40 required a new chassis.
The expectation for the final four-hour session was that track times would gradually drop with the track continuing to dry out, but the Circuit de Catalunya revealed on Twitter that they would use the lunch hour to wet the track once again.
— Circuit BCN-CAT (@Circuitcat_eng) March 2, 2017
Day Four timesheet (lunch break):
1) Kimi Raikkonen, Ferrari, 45 laps, 1:22.305;
2) Romain Grosjean, Haas, 49 laps, 1:22.739;
3) Stoffel Vandoorne, McLaren, 35 laps, 1:23.918;
4) Max Verstappen, Red Bull, 43 laps, 1:23.920;
5) Sergio Perez, Force India, 25 laps, 1:24.893;
6) Nico Hulkenberg, Renault, 51 laps, 1:24.974;
7) Antonio Giovinazzi, Sauber, 37 laps, 1:25.037;
8) Valtteri Bottas, Mercedes, 9 laps, 1:36.512;
10) Daniil Kvyat, Toro Rosso, 1 lap, no time
11) Lewis Hamilton, Mercedes, no laps, no time