Renault has written off the car that exploded during a fire in the Hungarian Grand Prix.
The team earlier explained the fire as due to overheating, after Nick Heidfeld revved the engine for too long during a pitstop delay.
Technical director James Allison on Thursday expanded by revealing that a different engine setting meant the exhaust was already running hotter than usual.
He said the exhaust also cracked, but the reason for the sidepod explosion was an "air bottle which supplies the air valves in the engine".
"It has overheated in the fire and failed," added Allison.
We are in touch with the FIA both to provide them with a full report of the incident
DPA news agency quotes him as saying the incident was "highly undesirable, as it has caused us to write off a chassis" just before the teams are forced to close their factories for the August break.
"We are in touch with the FIA both to provide them with a full report of the incident and also to explain to them the actions we are taking to prevent a reoccurrence," he said.