Lewis Hamilton will keep his new Mercedes engine - and crucial pole position - at Monza

Mercedes have traced the problem which forced Nico Rosberg to revert to an old-spec engine at Monza to "a leak in the cooling system", confirming the problem is not related to their new-spec unit which remains in Lewis Hamilton's pole-sitting W06.

Following evaluations of the upgraded engine overnight, Mercedes confirmed on Sunday morning that the new engine had been damaged by the cooling leak from a part which they have been using since 2014.

While Rosberg was forced to revert to the older engine he had used for the previous five races, Lewis Hamilton stayed with the upgraded unit and claimed his seventh pole in a role.

Confirmation that the fault wasn't directly related to the new engine will come as a relief to the world champion and should mean he doesn't have to make his own change and start from the pitlane.

"A leak in the cooling system led to contamination of Nico's engine - not a problem with the engine itself," a Mercedes spokesman said. "That unit will be inspected in the coming days to determine if it can be used again. ‎

Anthony Davidson outlines this differences between Lewis Hamilton's Mercedes and Kimi Raikkonen's Ferrari during qualifying for the Italian GP Anthony Davidson outlines this differences between Lewis Hamilton's Mercedes and Kimi Raikkonen's Ferrari during qualifying for the Italian GP

"You can never say never on the risk of a repeat but the part is of a design that hasn't changed since 2014."

With his used engine having inevitably lost horsepower since it was first introduced in Canada in June, Rosberg's speed was compromised as a result and he went on to qualify behind the Ferraris in fourth - his lowest grid slot for 27 races.

Despite spending all their remaining 2015 development tokens on the upgrade at Monza, Ferrari, who have made engine improvements of their own, got closer to pole than they have at any stage of the season in dry conditions.

Wolff admitted Ferrari's strong single-lap form was "a bit surprising" but stressed that Mercedes' upgrade was the first step on a longer-term development path and not about producing an immediate performance jump.

Ted Kravitz brings you all the latest news from qualifying at the Italian Grand Prix Ted Kravitz brings you all the latest news from qualifying at the Italian Grand Prix

"We ran Lewis's engine like we would run it normally in qualifying, so there wasn't any conservatism," he said.

"You have clearly seen that Ferrari made a step up with the engine and they've come closer. But as we said before, our engine is a new development direction, it is not a pure performance factor - there are other things behind it. So I wouldn't identify the engine as the factor that put us on pole, but good driver/car combination."