Jenson Button says that long runs in the McLaren MP4-29 are not as much fun as he'd hoped, after practice for the Australian Grand Prix.
Button was fifth quickest in second practice but warned that the race will provide a different challenge.
"In all honesty, these cars work better around here than I'd imagined, but Sunday's race will be very different," he said.
"The long runs weren't as much fun as I'd hoped they'd be, because you need to save a lot of fuel. And that's such a different way of driving - you're lifting off very early, and there's lots of lift-and-coasting around the lap."
Button was upbeat about the feeling of the MP4-29 across shorter low fuel runs.
"On low fuel, however, it's really fun to drive.
"Our car balance isn't quite there yet - we're still struggling a little in the high-speed corners. In the low-speed corners, we're looking reasonable, and all our electronics are working well.
"I don't think our outright pace is quite as good as it looks on the time sheets, but we've got a good understanding of the car and overall I'd say we're looking okay."
Team-mate Kevin Magnussen was ninth fastest and says he has been learning from the experienced Button.
"I've watched Formula 1 cars on this circuit on TV for many years, so it's strange to be driving here at last," said the Danish driver.
"But it was a good feeling to be out there on the track - I really enjoyed it. There's definitely an element of learning for me here this weekend, so it's good to have Jenson alongside me. He's so experienced, and of course he's very strong around here. I can learn a lot from him. The rest of the weekend is going to be really interesting."