Mercedes 'not bulletproof' as F1 testing setback forces 'engine change'

Mercedes have reportedly been forced into a change with their power unit during day two of F1 pre-season testing in Bahrain.

F1 is at the Bahrain International Circuit this week for the first of two three-day testing events before the start of the 2026 season.

There is triple the amount of testing on offer to teams this year, as F1 and the FIA give outfits a chance to iron out early issues that they might have with the wholesale new regulations changes.

At last month's private shakedown in Barcelona, however, all the teams enjoyed sound reliability, with Mercedes in particular impressing with over 500 laps worth of running over their three allocated days.

That led to rumours that they were the favourites heading into the season, but Bahrain testing so far has been a little tricky for them.

George Russell and Kimi Antonelli were only able to finish sixth and 11th respectively on the timesheets on day one in Bahrain, and on day two, Sky Sports F1's Craig Slater reported that an engine change was needed for the team.

Antonelli was only out for three laps on Thursday morning and failed to set a time, when he was forced to return to the garage. At time of writing, the Italian still hasn't been out on track and has lost most of the morning running.

During the morning session, Slater reported on the setback and said: "I am hearing about a potential engine change at Mercedes and they have their screens up.

"Red Bull and Mercedes are not entirely bulletproof in terms of reliability."

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Are Mercedes the favourites for 2026 success?

On top of their immense reliability in Barcelona, Mercedes also topped the timesheets on two of the three days in which they were running.

There has been talk of them being the dominant team in F1 this year throughout the winter, as it is believed they have found a clever trick with their power unit design that could equate to 0.3 seconds per lap.

The trick regards the geometric compression ratio, with it being reported that Mercedes have found a way for the compression ratio to be at the allowed 16:1 when the engine is stationary, but then increase to the previously allowed 18:1 when moving, something that could allow an extra 15 brake horsepower.

Mercedes, of course, dominated the sport the last time we had a wholesale regulations change in 2014, but suffered greatly during the more minor rule change of 2022.

Time will tell as to whether Mercedes really have found this extra pace or not ahead of 2026, but the Brackley outfit are looking in good shape to be able to mount a title challenge, or at least challenge closer to the likes of McLaren than they were last year.

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