McLaren has revealed that a bolt costing just £2 was responsible for the heat damage sustained by the MCL33 on Tuesday.
Stoffel Vandoorne had enjoyed a productive morning on day two of pre-season testing at the Circuit de Barcelona-Catalunya. He topped the time sheets early on with a swift lap on hypersoft tyres.
However, when he brought the car back to pit lane, some heat damage was detected on the bodywork
"Unfortunately we had this small issue with the exhaust clip," Vandoorne explained on the day. It had led to hot air blowing on the internal wiring looms - including those responsible for braking. The issue meant the team lost almost all of the afternoon running time.
"It's a stupid bolt that broke in the exhaust," McLaren sporting director Eric Boullier revealed on Thursday. "It was a £2 problem which cost us a lot of track time.
"Everything was burned after in the back of the car, so we had to rebuild the gearbox and the back end."
But Boullier was relieved that the cause hadn't been anything more serious requiring major revisions ot the car design.
"It didn't cost us much to revise the design, it's more about the track time we lost," he noted. "As you can see the design is still the same and the car is still running."
The team had already suffered problems on the opening day of the test when a faulty wheel net dumped Fernando Alonso in the gravel.
And on Thursday, a hole in the car's heat shield resulted in more delays. Fortunately the heat damage on this occasion was purely cosmetic and little time was lost.
"Cooling is the first matter that every team is managing in the first week of testing," Boullier explained.
"We have to make sure there are some proper heat shields in place," he continued. "Consider all the heat soak pockets, [and] make sure we can modify and change the cooling inside the bodywork."
Once the problem was taken care of, McLaren turned its final day focus onto aero data gathering.
"We obviously adjusted our programme, we have compressed it," he said, acknowledging that the loss of track time on Wednesday had been a set-back for the team.
"It's a learning process actually, so we'll try to learn as much as we can now."
Next week the team will turn its attention to distance runs, with the first race of 2018 now only a little over three weeks away.