The Australian took over the new McLaren MCL40 for the first time as teams continued to balance cautious mileage gathering with early problem-solving under the sport’s radically new regulations.

Piastri’s debut day, however, was cut short when McLaren encountered a fuel system issue that kept the car in the garage for much of the afternoon.

Piastri completed 48 laps in total, ending the day fourth on the unofficial timesheets, with all of his meaningful running confined to the morning session.

McLaren opted not to rush the car back out as it investigated the problem.

“It was nice to be back out today, especially in the new car,” Piastri said.

 

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“There’s a lot of challenges this year up and down the grid, so it was good to get stuck in.

“We had a fuel system issue, which cut our day short, but the team’s working hard to get that fixed and back out tomorrow.”

McLaren performance technical director Mark Temple explained the cautious approach.

“The car is very complex, so we decided to bring the car back into the garage and strip it down to fully understand where the problem is coming from, ahead of tomorrow’s running,” he said.

While McLaren lost valuable time, Mercedes once again underlined its strength by continuing to pile on mileage.

George Russell and Kimi Antonelli shared duties in the W17, with Russell setting the fastest time of the week so far at 1m16.445s during the afternoon.

Mercedes has now completed its full three-day allocation at the Barcelona shakedown, racking up close to 500 laps across the test with largely trouble-free running.

Antonelli said the team would leave Spain encouraged despite minor setbacks earlier in the week.

“We go [to Bahrain testing] with high confidence and high hopes because, definitely, it’s been good,” he said.

“Obviously, we had our issues during the shakedown, but we were able to fix them and now we can be sure that in Bahrain we can more or less hit the ground running there as well.”

Aston Martin finally appeared on track for the first time this week but endured a frustratingly brief outing.

Lance Stroll took the unpainted Adrian Newey-designed AMR26 out in the final hour and completed just a handful of exploratory laps before grinding to a halt and triggering the only red flag of the day.

The stoppage brought the session to an early conclusion, with no immediate explanation offered for the issue. Aston Martin is now hoping for a clean final day on Friday, with Fernando Alonso expected to drive.

Ferrari, by contrast, enjoyed a productive day in dry conditions after running in the wet earlier in the week.

Lewis Hamilton and Charles Leclerc combined for more than 170 laps in the SF-26, with Leclerc finishing as the closest challenger to Mercedes on outright pace.

Elsewhere, Racing Bulls completed its final permitted day of running with Liam Lawson and Arvid Lindblad, while Sergio Perez logged further mileage for Cadillac.

Alpine, Audi, Haas and Red Bull all sat out Thursday’s action, with Red Bull continuing repairs after Isack Hadjar’s heavy crash earlier in the week.

With one final day of running remaining in Barcelona, Piastri and McLaren will be keen to get back on track and recover lost mileage before the focus shifts to the more representative Bahrain test next month.

Results: Formula 1 pre-season shakedown Day 4 (unofficial)