The turmoil at McLaren deepened Tuesday when development driver Oliver Turvey missed most of testing in Bahrain with an engine leak, as Lewis Hamilton went fastest in his Mercedes.
At the weekend Bahrain Grand Prix McLaren's Fernando Alonso complained he had never raced with so little power, while his teammate Stoffel Vandoorne had no power at all after engine failure prevented him even starting Sunday's race, which was won by Ferrari's Sebastian Vettel.
During in-season testing on the same circuit Tuesday McLaren detected a water leak on the first lap and worked all day to repair it, completing only 17 laps and two timed runs.
"I'm really grateful for giving me the opportunity to drive here in Bahrain. It's frustrating to have had an issue this morning which cost us a lot of track time," Turvey said having waited all day to get back behind the wheel.
Stoffel will complete the testing on Wednesday.
McLaren have produced a promising chassis this season but have been unable to show its potential because of Honda's failure to deliver a reliable engine.
Mercedes by contrast completed 97 laps and Hamilton was fastest on the day at 1min 31.358sec ahead of Antonio Giovinazzi for Ferrari at 1min 31.984sec and Daniel Ricciardo for Red Bull at 1m 32.349sec.
"Today was tricky with it being so hot and very gusty but we still managed to get through plenty of work," Hamilton, second to Vettel on Sunday, said.
"Our focus was on advancing our understanding of the tyres and also the rear of the car so that we can improve our long runs."
Hamilton's Mercedes teammate Valtteri Bottas will be behind the wheel on Wednesday.