Stoffel Vandoorne says McLaren and Honda must get to the bottom of why the team's final day of Formula 1 testing in Bahrain was so good.
After McLaren suffered a difficult Bahrain Grand Prix weekend and restricted opening day of running in the post-race test, Vandoorne managed to set the fourth fastest time and complete 81 laps on the final day.
The situation was slightly puzzling for McLaren because the engine was the same specification as the one that had hit trouble after two laps on the first day.
When asked by Autosport about whether he felt McLaren needed some good news after a run of difficulties, Vandoorne said: "I don't think we need one day, we need it to be all the time like this.
"So yeah, it was good but there is no guarantee that the next time it will be good again.
"We need to learn carefully what we've done today and hopefully carry that forward to the next event and see some improvements. Days like this are how it should be."
Vandoorne said the full day of testing had allowed McLaren to work on understanding its chassis.
"From the team's point of view it was very good to go in different directions," he said.
"There were some new bits that we wanted to try out: some quite fundamental things which we had to learn about.
"That was good for the team to see where the performance comes from and also good for me to know which direction the car is performing better. So a productive day."
Vandoorne hopes that any momentum McLaren can gain from the test can be capitalised on with further updates for upcoming races.
He added: "The baseline of the car is pretty strong, during the weekend I actually felt comfortable in the car and chassis is behaving well.
"Over the next few races we will bring some more bits to the car and eventually we will get strong.
"But we know that our biggest deficit is still the power and there is a lot of laptime to be gained with that so, hopefully we can from our side bring new pieces to the track and show that the car is going in the right direction.
"We need to see when the power unit will make a step forward."