Mercedes has revealed that Nico Rosberg's poor start at the Japanese Grand Prix was not helped by his engine running hotter than teammate Lewis Hamilton's.
Although both drivers got away well when the lights went out, the second phase of Hamilton's start was better because Rosberg was held back by a slight power deficit caused by his engine running at a higher temperature.
Mercedes motorsport boss Toto Wolff explained: "The initial getaway was good for both cars. Nico had a little bit of an issue with a hotter power unit and when it kicked in after a couple of seconds, he didn't have same power as Lewis."
Wolff said that the issue had come to light before the start, but there was no answer yet as to what had caused it.
"It was showing up on the formation lap," he said. "I haven't got an explanation yet but there was definitely a slight drop in power due to a temperature related issue.
"We don't know yet if it was down to the driver, but it affected him the whole race – and definitely affected him in the fight at Turn 1 and Turn 2."
Rosberg's hopes of winning the Japanese GP were effectively killed off at Turn 2, when Hamilton held the inside line and forced him out wide.
Although some have suggested that Rosberg should have been tougher in defending against his teammate, Wolff is not convinced he could have done much more.
"I don't think it has anything to do with being soft or not; it is always very difficult to race your team-mate," he explained.
"We have seen great racing afterwards with [Valtteri] Bottas, and it was a tricky situation for both.
"Lewis said he had understeer in the car and he ran out of track. Two cars side-by-side through Turn 2 is difficult anyway."