Both Mercedes drivers were hit by an unexpected overheating problem with the Motor Generator Unit (Kinetic) in Canada, and it was just bad luck that saw Lewis Hamilton retire while Nico Rosberg was able to carry on.
The problems arose around the time of the second stops, just as Hamilton passed Rosberg for the lead. It was the time spent at rest in the pit lane – with no cooling air going through the system – that tipped Hamilton over the edge and led to his retirement.
Rosberg was forced to run the remainder of the race without the benefit of power derived from recovered braking energy.
“We had a failure of the engine control systems on the ERS, on the MGU-K,” said Mercedes F1 boss Toto Wolff. “We had a peak in temperatures. They had exactly the same power units and they were racing at exactly the same pace and had exactly the same temperatures. In that particular part of the MGU-K we saw temperatures which were higher than expected, but we weren’t aware that they could have such a detrimental effect. The MGU-K just shut down, and we couldn’t reset it.
“We are keeping all those temperatures under observation, and we know where we are critical and where it’s important. In that case it was something that we didn’t spot before. It’s just another part which we have to analyse and understand, and I guess this can happen. The consequence was obviously detrimental to the whole car, to the brakes.
“We told both drivers to manage the brakes, because when you lose the electric motor, you lose the electric braking. The brakes were overheating massively, so we changed the balance within the braking system, and told them to be more careful. It’s what both of them did, both of them complied to exactly what they’ve been told. It’s very marginal – Lewis entered into the pits, the car is static, the temperatures rise, and when he went out the pedal just went soft and then fell down completely. On Nico’s car he was lucky not to have that.”
Wolff was full of praise for Rosberg’s efforts: “It was really damage limitation for him, so what a drive.”