Both Piastri and team-mate Lando Norris got behind the wheel of the car in wet conditions in what was officially classified as a filming day.
Teams are allowed 200km of running under the guise of promotional filming.
It followed an outing in the 2022-spec car in Barcelona for both drivers earlier this week.
“No surprises today, really,” Piastri told invited media, including Speedcafe.
“Felt pretty comfortable and went smoothly, which was good.
“But you never really know what you’ve got until you compare it to other people, so I think we’ll have to wait a little bit longer to see what we’ve really got.
“But as these days go, that was smooth sailing.”
McLaren opted for a low-key launch of its new car, releasing just three images of the MCL38.
Even those had areas redacted as the team worked to keep some of its development ideas under wraps.
The content posted to the team’s social media was also carefully moderated to not offer rivals a look at parts of the car.
“Sometimes you may want to have just a lower profile in launching your car,” ventured Stella when asked why the team opted for the approach it did.
“We went from last year’s glamorous one to this year, which is low profile.
“This is not only technical or operational aspects, this is also marketing and commercial.
“Formula 1 is a large business. It’s not only technical, like I say, and we need to take into account all these requirements and variety of approaches.”
“At least we showed our car before it went on track, unlike others,” quipped Piastri.
McLaren effectively had two bites at the cherry, with its livery reveal in January followed by the car launch itself on Wednesday.
Despite the secrecy surrounding some areas of the car, and manipulation of the images revealing the MCL38, Stella suggests there are no major secrets lurking within those areas.
“I would say pretty accurate,” he opined when asked how close the images released are to the actual car.
“I wouldn’t be prepared for anything too shocking.
“To be honest, even myself, I needed to look at the pictures like ‘okay, yeah, yeah, a detail [has been hidden],” he added.
“So nothing too major.”
Following Mercedes’s launch earlier in the day, Red Bull Racing the only team yet to reveal its 2024 car as F1 prepares to head to Bahrain for pre-season testing next week.
Three days of running are scheduled from February 21-23.
Feeling at home! 🧡
The #MCL38 takes to Silverstone for its track debut. 💫 pic.twitter.com/DHDAKh8XGp
— McLaren (@McLarenF1) February 14, 2024