Sebastian Vettel led the way on the penultimate day of F1 testing at the Jerez de la Frontera circuit in the extreme south of Spain.
The German, who took his maiden win at the Italian GP last weekend with Scuderia Toro Rosso, was again behind the wheel of a Red Bull-Renault RB4 - like he was on Wednesday - and despite being delayed by an unscheduled engine change, he finished proceedings at the top of the times, on a 1 minute 18.001 seconds.
Vettel spent the morning working through an aero and a mechanical comparison test, which apparently produced 'positive results'.
In the end though he only did 37 laps in total, as rain later on in the day, saw the team end its programme prematurely.
Nick Heidfeld ended the session 'best of the rest', just under two tenths slower on a 1m 18.167s. The German worked on the mechanical and aerodynamic set-up of the BMW Sauber F1.08 early on, evaluating different configurations for the remaining races of the 2008 season.
When rain arrived around lunch time, he continued running, albeit with his focus altered: "As we might have some rain during the forthcoming races we took the opportunity to work on the car's wet weather set-up," he explained.
Lucas di Grassi came in third for Renault, the only other runner to break the 1 minute 19 second barrier. He ran mostly in the morning, as the team continued with its aero programme and evaluated various updates for the R28.
"It was quite cool today but the track conditions were good in the morning and there was definitely better grip than yesterday," said di Grassi. "I'm also getting used to the car and the more laps I do, the more confident I feel. We didn't do any running in the wet, but we were able to test a few more parts this morning that the team will be taking to the race next week."
"A slightly challenging day for us as we didn't get all the test results we wanted to and the day finished early due to poor weather," added Renault's chief test engineer, Christian Silk. "However, we managed to cover the main items this morning, so it's not been too bad and we've got some interesting data to go through this evening. Hopefully it will be dry tomorrow and we can get a good final day of testing in."
Further down the order McLaren's Pedro de la Rosa and Honda's Alex Wurz rounded out the top five, split by less than three tenths of a second.