Pat Symonds: Unsure if Williams will use upgraded Mercedes engine

Williams chief technical officer Pat Symonds admits he doesn't know if the team will run Mercedes' upgraded engine during 2015.

Lewis Hamilton romped to victory at Monza in the works Mercedes car, running the new power unit which is thought to be worth up to 40 extra horsepower.

However, despite the benefits, only one of the Silver Arrows was able to run the unit after Nico Rosberg suffered reliability problems, leading to him switching to an old engine.

Thus, Symonds is wary of taking the new unit before it is fully understood and he still has faith in the specification Williams currently use.

"To be honest I don't know," Symonds told Sky Sports when asked if Williams would use the new Mercedes engine this year.

"There is obviously some risk analysis to be undertaken to know whether to use the new power unit or not. I think we are incredibly satisfied with what we have got, we have got the best power unit in Formula 1 and Mercedes allow us to use it very, very aggressively. So we feel it is a very reliable and a very powerful unit and that is great for us.

"We are competitive people and we always want the next best thing, but I think we will be guided by the works team by how they get on - remember they have only done one race with one car with that power unit and there will be a lot of inspection going on.

"What it is really good to see, though, is that they are not resting on their laurels, they are the dominant power unit, yet they are still pushing really hard for 2016."

Williams still have one penalty free engine to take on both cars this season, but will take advice from Mercedes on when to introduce that unit and indeed in what specification.

"We have got a fourth engine to take, maybe somewhere around America, maybe Russia, we will see how it goes," Symonds added.

"But we want to take our guidance from Mercedes, we don't want to take risks. We will see what they think is the best engine for us."