Mercedes team boss Toto Wolff admitted on Friday that the German manufacturer's ongoing engine reliability issues are "not trivial" after three fresh units were deployed in Austin for this weekend's US Grand Prix.
Yesterday, it was announced that a new engine was supplied to Aston Martin's Sebastian Vettel for this weekend, while on Friday, Williams also received a complete new unit for George Russell, changes that will send both drivers to the back of the grid on Sunday.
During FP1, Mercedes revealed that a sixth ICE had been allocated to Valtteri Bottas, a change that will also warrant a grid drop for the Finn.
Added to the changes that occurred in Russia and in Turkey, Mercedes appears to be struggling to solve its reliability concerns, a fact that Wolff did not deny, alluding to a chronic issue that "keeps coming back".
"I think we understand now much better what it is," Wolff said. "But it means that there is no durability in running them and that means that's potentially a DNF risk."
©Mercedes
In Friday's team principals media conference, Wolff explained that the lingering reliability issues were also pushing Mercedes to the fringe regarding its supply of hardware to its customers.
"I think you see that we are suffering with reliability this year," said the Austrian.
"We're going onto the sixth engine, I believe it is for Valtteri, and it's not something that we choose to do.
"But on the contrary, we're trying to really get on top of the problems, and we haven't understood [them] fully.
"I think we are a step closer now, so it's not always that we are literally easy with having the engines.
"We are hanging on for dear life in supplying all customers, and that is not trivial."
Wolff said that Mercedes' fierce battle in the championship against Red Bull has led to a performance push, but one that has come to the detriment of reliability.
"I think that when you look at Monza, for example, Valtteri had to start from the back, and we are losing points on the way," he added.
"We are trying to push the performance every year, and this year, we've come to a point where that has cost us points. Over the last seven or eight years, that mindset has won us races and championships.
"So I would have hoped for a few less penalties and use less engines, but this year it has really hit us hard.
"McLaren and Aston Martin are more fortunate, and in that respect, we just have to take it on the chin and do the best possible job."
McLaren's Zak Brown said the team had no concerns over the reliability of its customer engines, saying Mercedes had been "pushing extremely hard".
"There's great competition, so when you're pushing, that's going to always challenge reliability," Brown said.
"But I've got to say from a McLaren point of view, we're very happy. They've got an unbelievable track record, so we're not concerned."
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