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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.

Alex Palou fastest as several go off course during IndyCar practice at IMS

IndyCar Harvest GP practice
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Alex Palou paced the opening practice Thursday for the IndyCar Harvest GP at the Indianapolis Motor Speedway road course.

The Dale Coyne Racing rookie turned a 1-minute, 10.177-second lap around the 2.439-mile, 14-turn road course in his No. 55 Dallara-Honda.

Jack Harvey was second, followed by Colton Herta, points leader Scott Dixon and Max Chilton.

PRACTICE CHART: Click here to see the speed rundown from Thursday’s session

FRIDAY AT IMS: Details for watching Race 1 of the Harvest GP

Qualifying for Friday’s race will be at 6:20 p.m. ET Thursday on NBC Sports Gold.

Will Power, who won the pole position for the July 4 race at the track, spun off course with just more than a minute left in the session after the left rear of his No. 12 Dallara-Chevrolet made slight contact with the right front of Alexander Rossi’s No. 28 Dallara-Honda.

Power was among several drivers who went off track, but there were no damaged cars during the session. Marcus Ericsson missed the final 5 minutes of the practice after being penalized for causing a red flag with a Turn 8 spin.

Arrow McLaren SP drivers Pato O’Ward and Helio Castroneves, who is driving for Oliver Askew (who is recovering from concussion-like symptoms), also veered off course as did rookie Rinus VeeKay and Santino Ferrucci.

Seven-time NASCAR Cup Series champion Jimmie Johnson was in attendance at the session before racing Sunday at Talladega Superspeedway. Johnson will be driving a partial schedule of road and street courses in IndyCar next season for Chip Ganassi Racing.

“Literally, the smallest of details, I can pick up on,” Johnson told NBC Sports pit reporter Kevin Lee. “It’s been really nice today just to see how a session starts and obviously to jump on the radio and listen to how the systems work and then obviously you get into the car and the setup and such. I’m at ground zero right now, a 45-year-old rookie trying to learn my way into a new sport essentially.”

Johnson told Lee his sponsorship hunt to run a Ganassi car “has gone really well. The fact that I’m here today and ingrained so deeply in the team is a great sign of where things are going. Looking forward to getting behind the wheel of a car soon and hopefully having some announcements for the world to see soon, too.”

Fans were in attendance Thursday for the first time this season at IMS, which is allowed a limited crowd of 10,000 for its races this weekend.