McLaren-Honda says a faultless day of running on the final day of F1 testing in Bahrain represents its own issues since it is yet to get to the bottom of the engine problems that forced it to change its MGU-H four times in four days.

After Oliver Turvey managed just 17 laps on the first day of the F1 test, Stoffel Vandoorne finally enjoyed a trouble-free day at the wheel of the MCL32, notching up 82 laps - more than his race laps from the three rounds combined.

However, when asked whether the problem-free day marked a 'glimmer of hope', McLaren Racing Director Eric Boullier says this is on the contrary since adds a 'complication' for Honda to investigate an issue that could occur after 'two laps or two days'.

"No, because it's very difficult to understand what's going on," he contested. "We obviously changed the MGU-H four times and yesterday morning, two laps, MGU-H gone, changed the engine, did 17 laps yesterday. This morning we had a small alert but we couldn't find anything wrong physically on the car and then since then we've run faultlessly, without any problems.

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"So I think it's going to be complicated for Honda to understand what's wrong, it could maybe be coming from some batch problems. I don't believe it is a car build problem but we can't find what's wrong, you know? We can do two laps or we can do two days."

Nevertheless, Boullier was pleased to see Vandoorne get enough laps in to get some much-needed data on the car.

"No, we had good days last year as well I think. But today we are following the test plan and a lot of information has been understood and solutions tested on the car. So a very good test in terms of data and results."

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