Toto Wolff says an engine issue nearly derailed Nico Rosberg's easy win at the Russian Grand Prix.
Rosberg led away from pole and was never threatened during the race, with a water pressure issue at mid-distance nullifying the chance of any challenge from Mercedes teammate Lewis Hamilton behind. However, team boss Wolff says there was also a problem on the No. 6 car during the race that the team believed at one stage to be terminal.
"We had a problem on Nico's car which gave us some grey hair during the race, a problem on the MGU-K drive," he said. "It looked like at a certain stage he wouldn't finish the race. So we are pushing the limits on the chassis and on the engine side a lot in order to have a competitive car and this is why we are winning races but also if you push the limits at a certain stage you mess up."
Mercedes' reputation for reliability has wavered slightly in recent races, with Hamilton suffering identical MGU-H failures in qualifying for China and Russia. Wolff says the threat of Ferrari this year means the team is pushing the engine more than it had to in previous years.
Asked if Ferrari's improvement over the winter has forced Mercedes to delve into unknown areas of its engine, he agreed and said: "The more the regulations stay stable the more difficult it is to find performance. Andy Cowell and his team, he is Mr Performance and he is pushing the guys to extract every millisecond out of that engine.
"Because of the stable regulations it becomes more difficult and sometimes you need to push the boundaries to find the limits and maybe this is where we are at the moment, but I have no doubt this is a bunch of great engineers and great people and that we are going to solve. And fundamentally we have finished with a one-two so despite all the grey hairs in the race we still got a really brilliant result."
The win was Rosberg's seventh in a row, a run stretching back to last year's Mexican Grand Prix, and extends his championship lead to Hamilton to 43 points after just four races.
Rosberg's lead had dropped to seven seconds before Hamilton had the issue but the German says he was managing the lead because he had been made aware of the problem.
"For sure I lost a fair chunk of performance because I had to turn everything down. But of course I had a healthy lead and was aware Lewis was dropping off, although I wasn't aware that he was also having to turn things down. I just saw him dropping off and though it was the tyres because he definitely did use them more earlier in the stint, but we both had to turn things down."