The Finn was forced to use his sixth internal combustion engine of the season at the United States Grand Prix, a change which resulted in a five-place grid penalty. 

It marked a third grid penalty in four races for Bottas, who faced back-of-the-grid starts at both the Italian and Russian grands prix in September. 

Starting ninth at the Circuit of the Americas, Bottas was only able to recover to sixth as Red Bull reduced Mercedes’ advantage at the top of the constructors’ world championship to 23 points. 

“I really hope we’re done for now,” Bottas said after the race in Austin. "Having both of the engines that are good in my engine pool, they seem to be OK – we haven’t detected any issues in either.

“Fingers crossed I can go to the end now without penalties, because with a close championship, when you get put back five places, it really compromises your race.” 

Bottas has been the Mercedes driver most affected by the engine reliability issues, with teammate Lewis Hamilton only using four ICE components, having taken a grid penalty at the Turkish Grand Prix. 

“I think it's been just a question of I’ve been a bit more unlucky,” Bottas added. “It’s just before you fit the engine they have passed all the all the tests and reliability checks, and in theory they should be okay. 

“But just the luck has not been on my side on that, we've had more failures and just unlucky. But we really hope that we've now fixed everything, but time will show.”

Mercedes strategy director James Vowles explained in the team’s post-US Grand Prix debrief video that it is “balancing performance versus reliability to the end of the season.” 

“One failure to finish a race because of a chassis or power unit fault would be catastrophic for the championship and as a result of that, we are managing that in the best way possible to the end of the year,” Vowles said. 

“In the case of Valtteri, that meant taking one further ICE to make sure we had absolutely the best compromise.

“As to whether it improved his performance – yes, a small amount, but it is more about the balance across the remainder of the season than one event.

“This change, as painful as it was during the US Grand Prix, will actually pay dividends across the next few races.”