At the Turkish Grand Prix last time out, Lewis Hamilton took a new ICE (internal combustion engine) as Mercedes was fearful that he wouldn’t make the end of the season without a DNF, while Red Bull has already taken entirely new power units with both of its drivers. 

Just six points separate Max Verstappen and Lewis Hamilton at the top of the drivers’ championship with six rounds remaining. 

“Definitely reliability is going to be a key factor obviously a second engine penalty is only five places on the grid now, so it's not anywhere as significant as the first one but reliability is going to play a key role, it's a question of making the right calls at the right time and keeping your head, keeping your nerve and doing the basics well,” Horner said in Turkey.

Horner remains confident either Verstappen or Perez will be forced to take another engine penalty.

“I think in normal circumstances we should be able to do it with the penalty that we took in Sochi,” he explained. “That gives us three engines still alive in our pool, we're not bound to just one engine so theoretically we should hopefully be able to get to the end of the year but never say never.”

Mercedes enjoyed a significant performance advantage over Red Bull at Istanbul Park with Valtteri Bottas beating Verstappen to the victory by over 14 seconds.

Horner confirmed his team will be doing a thorough analysis to understand why Mercedes was so strong in Turkey.

“Formula 1 being the business that it is we have a whole bunch of analysis looking at all elements whether it's a power unit, whether it's grip levels, whether it's whatever, specifics to our car, our competitors, that's the nature of the game,” Horner added. “I'm sure that the serious teams will be looking as well so you're always learning in this business and on a day like today you're going by the seat of the pants because what the simulation data tells you, you've got to react to what you can see and what the drivers are feeling.”