Lotus believe a loose visor tear-off is to blame for Kimi Raikkonen's Belgian GP retirement as it got stuck in his E21's brake cooling duct.
For the first time since returning to Formula One with Lotus last season, Raikkonen failed to reach the chequered flag at Spa.
Battling for what would have been his 28th consecutive finish inside the points, the Finn was forced to park his car on lap 26 with brake issues.
It was later revealed that a tear-off visor had become stuck in Raikkonen's left front brake duct, causing his brakes to overheat.
"We know that we have two options on cooling here: one was nearly too cool, one was on the top of the range," team boss Eric Boullier told Autosport.
"If the failure had happened on both discs then you would think that the cooling was wrong, but it was only on one disc."