Jenson Button kept McLaren on top in the second practice session at Istanbul, with Red Bull's Mark Webber and Sebastian Vettel second and third despite some reliability worries in the closing minutes.
McLaren resumed its morning superiority early in the session, with Lewis Hamilton and Button first and second following the initial runs. Indeed, at the halfway point, afternoon practice looked extremely symmetrical, with the two McLarens heading the Red Bulls, Mercedes, Renaults, Saubers and Force Indias in two by two formation through the top 12.
The neat order was shuffled soon afterward. Hamilton switched to softer tires with 40 minutes to go and trimmed 0.02sec from his time to get down to 1m28.672sec – but moments later Vettel went quicker still on the same tires, lapping in 1m28.590sec. He stayed in front for five minutes before Button put McLaren back in front with a 1m28.280sec lap, which remained the best of the session.
Webber then took second from Vettel, but the afternoon came to a worrying end for Red Bull as the Australian came to a halt on track five minutes from the end, with wisps of smoke from the car's rear. While he neatly reversed the car back behind the barriers, Vettel was already expressing concern over his water pressure via the radio, giving the championship-leading team cause for some reliability anxiety.
Hamilton remained fourth until the end, with Fernando Alonso bringing Ferrari up to fifth by the checkered flag after a low-key start to the afternoon.
Mercedes was sixth and seventh, Nico Rosberg ahead of Michael Schumacher this time, followed by the Renaults and Felipe Massa in the second Ferrari.
Turn 8 continued to cause headaches for drivers. Tonio Liuzzi caught a high-speed half-spin at the long, fast corner without emulating his Force India teammate Adrian Sutil's morning impact with the barriers.
Three-time Istanbul winner Massa had a few early scares at Turn 8, too, before later snapping into a wild slide that – like Liuzzi – he caught just before it turned into a full spin, though his long sideways drift still ruined his soft tires.
Pos Driver Team Time Laps
1. Button McLaren-Mercedes 1:28.280 30
2. Webber Red Bull-Renault 1:28.378 + 0.098 24
3. Vettel Red Bull-Renault 1:28.590 + 0.310 26
4. Hamilton McLaren-Mercedes 1:28.672 + 0.392 32
5. Alonso Ferrari 1:28.725 + 0.445 30
6. Rosberg Mercedes 1:28.914 + 0.634 22
7. Schumacher Mercedes 1:28.974 + 0.694 22
8. Kubica Renault 1:29.225 + 0.945 34
9. Petrov Renault 1:29.501 + 1.221 36
10. Massa Ferrari 1:29.620 + 1.340 26
11. Sutil Force India-Mercedes 1:29.629 + 1.349 16
12. Hulkenberg Williams-Cosworth 1:29.987 + 1.707 17
13. Kobayashi Sauber-Ferrari 1:30.053 + 1.773 34
14. de la Rosa Sauber-Ferrari 1:30.176 + 1.896 34
15. Buemi Toro Rosso-Ferrari 1:30.386 + 2.106 32
16. Liuzzi Force India-Mercedes 1:30.627 + 2.347 28
17. Barrichello Williams-Cosworth 1:30.766 + 2.486 32
18. Alguersuari Toro Rosso-Ferrari 1:30.933 + 2.653 37
19. Kovalainen Lotus-Cosworth 1:31.610 + 3.330 37
20. di Grassi Virgin-Cosworth 1:33.013 + 4.733 28
21. Trulli Lotus-Cosworth 1:33.081 + 4.801 11
22. Glock Virgin-Cosworth 1:33.312 + 5.032 29
23. Senna HRT-Cosworth 1:33.420 + 5.140 35
24. Chandhok HRT-Cosworth 1:33.740 + 5.460 25
All Timing Unofficial