Lewis Hamilton has faith that his Mercedes Formula 1 team is doing all it can to get on top of its engine reliability problems before the Australian Grand Prix.
While the new Mercedes W11 has emerged from winter testing as the car that many believe to be the fastest, it has not been an entirely smooth two weeks for the German manufacturer.
It had to use two engines in the first test, after a power unit on Valtteri Bottas's car failed following two days of running in week one.
That unit was then checked and given the all clear and put back in the car for the final day of this week's test, after Hamilton suffered an oil system anomaly on Thursday afternoon.
Williams also had to run three engines in testing, giving Mercedes more reliability headaches as it finalises the specification it will take to Melbourne for the first race.
Autosport understands the engine issues Mercedes is suffering from are not identical, so solving the initial problem may have opened up an unexpected issue elsewhere.
Hamilton said it has become harder and harder for engine manufacturers to extract more performance from the power units.
Asked by Autosport about the engine dramas, Hamilton said: "It was a difficult winter last year, and I think it's been a difficult winter this year.
"There was a period of time with this V6 turbo where we were just gaining, gaining, gaining, gaining and gaining.
"But eventually, like with everything, you get to the point with limited returns.
"So it's how much more can you squeeze out of the V6 turbo? How much further can you go?
"We are kind of in that peak top speed area now: where there is one kilometre more or one kilometre less you are gaining, for a lot of investment.
"But I fully believe in trusting the guys to be methodical with the way they move forwards and the engine is actually very good. It's an improvement from last year.
"It's just not quite where we want it to be reliability wise.
"But I am sure they are back at the factory now working hard to rectify whatever the issue is."
Racing Point technical director Andy Green, whose team uses customer Mercedes engines and got through the test without reliability dramas, said that the problems other squads experienced did not come out of the blue.
"I think HPP [Mercedes' High Performance Powertrains] are aware of the issues over the last few weeks and have known containment measures in place," he said.
"I don't think they are worried.
"They tell us they are not worried, so we are not worried.
"We think we will be in a good place come Melbourne. This is testing, this is what it is all about.
"I think [these were just] some teething problems.
"None of these are unknown problems, these are known problems that they have fixed."