The BMW Sauber and Williams teams are being investigated by Brazilian Grand Prix stewards over possible technical irregularities on their cars at the end of Sunday’s Interlagos race.

The enquiries relate to fuel temperature, which under Formula One racing’s technical regulations are not allowed to fall more than 10 degrees Celsius below ambient air temperature at any time. According to FIA data, Williams and BMW Sauber exceeded this range.

Nico Rosberg finished fourth for Williams, with Robert Kubica and Nick Heidfeld fifth and sixth respectively for BMW Sauber. If they were to be disqualified, it would move McLaren’s Lewis Hamilton up from seventh to fourth, making him world champion, rather than Ferrari’s Kimi Raikkonen.

Raikkonen won the race from team mate Felipe Massa, with McLaren’s Fernando Alonso third.

A statement from the sport's governing body, the FIA, said the fuel in the cars was "more than [the permitted] 10 degrees below the ambient temperature". The statement said Heidfeld's fuel was 13C lower than ambient at his first stop and 12C lower at his second. Kubica's varied by 14C, 13C and 13C at his three stops, while Rosberg's was 13C and 12C out at his two stops.

Filling the car with cooler fuel can give a performance advantage. Cooler fuel is denser, so either it can mean it takes slightly less time to refuel the car or marginally more can be added in the same time. And it would give a slight power advantage for about three laps before it returned to ambient temperature out on the track. Excluding the cars would have risked turning one of the most exciting championship finales in F1 history into a farce.

But the stewards had the power to disqualify them, even though the advantage conferred would have had no bearing on the title race. The total advantage for each car over the race distance was almost certainly no more than a second.