Mercedes: Rosberg power unit change forced by cooling system leak

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Mercedes has discovered the cause of the issue on Nico Rosberg’s power unit that forced the German to revert back to a previous specification model on Saturday.

Mercedes opted to spend all seven of its remaining 2015 development tokens to upgrade its power unit ahead of this weekend’s Italian Grand Prix.

The advantage that it offered was clear in practice as Rosberg and teammate Lewis Hamilton dominated proceedings on Friday.

However, Rosberg was forced to switch back to his power unit from the Belgian Grand Prix on Saturday after Mercedes discovered an issue on his new one, denying him the updates for qualifying.

With this setback, Rosberg could only qualify fourth at Monza behind Hamilton and the Ferrari duo of Kimi Raikkonen and Sebastian Vettel.

Rosberg confirmed to NBCSN that Mercedes knew what had happened to the power unit, but was yet to define the cause.

A full investigation has now revealed that Rosberg’s power unit was contaminated by a leak in the cooling system, meaning that there was no issue with the engine itself.

As a result, it is unlikely that Hamilton’s upgraded power unit has been compromised, allowing him to start today’s race from pole position as planned.

The Italian Grand Prix is live on NBCSN and Live Extra from 7:30am ET.