The Finn covered a distance of 783km on Wednesday, clocking a fastest lap of 1:38.490s on Pirelli's new for 2018 HyperSoft tyre, as the championship-winning W08 made its final on-track appearance before retiring.
"It was a really interesting day, trying out the new Pirellis and discovering the differences between this year's and next year's tyres," he said.
"I could really feel the differences and it was nice to get the feel now rather than next year. We tested all kinds of compounds and learned a lot out of all of them.
"I myself learned a great deal about the driving style with these new tyres. Now I'm looking forward to get some holidays."