The new Red Bull car finally got down to serious mileage as pre-season testing reached the halfway point.
Sebastian Vettel completed 59 laps in Bahrain on the second day of the second four-day test. Red Bull had done only 24 laps in the previous five days.
The world champion was seventh fastest overall, more than five seconds off the pace set by McLaren's Kevin Magnussen.
Force India's Nico Hulkenberg was second from Ferrari's Fernando Alonso and Mercedes' Nico Rosberg.
Magnussen was 1.535 seconds clear of Hulkenberg, with Alonso 1.606s behind the Dane and the Ferrari 0.449s ahead of Rosberg.
Vettel was seventh fastest, 5.430 seconds slower than Magnussen and 2.705s behind fifth-placed Valtteri Bottas of Williams.
"We did more laps today than so far the whole year, which is a step forward," said Vettel.
"We are learning every lap so we are trying to run as much as possible even if the quality of the lap is not the best, but the most important thing for us at this stage is simply to run."
Red Bull's testing campaign had been delayed by a multitude of problems affecting both the car and its Renault power-unit.
But Renault, whose testing has been afflicted by problems with hardware and software control systems, finally got its engine to a point where its teams could do proper testing mileage.
Red Bull boss Christian Horner said the team had the overheating problems that had plagued them at the first test in Spain last month "under control", although the team still had mechanics with fire extinguishers at the ready whenever the car returned to the pits.
Horner added: "The problems have been varied. We've had some problems on our side and a few problems on the Renault side but this is what testing is for.
"You aim to come to these venues to try to understand what issues you've got and work your way through them and that's exactly what we've been doing."
Mercedes, who have had the most reliable engine so far, had to stop a race-simulation run for Rosberg following sensor failures.
Magnussen and Hulkenberg set their fastest times on the super-soft tyre. Magnussen was on a series of one-off laps as McLaren appeared to be getting their novice driver used to the feel of the car on low-ish fuel and new, grippy tyres.
Apart from Caterham's Kamui Kobayashi, who went sixth overall with a late run on soft tyres, no-one else used either of the two softest tyre options.