Others are right. As long as he's in close proximity to other cars on the track, he will remain heated up. The more cars near him, the more likely & longer he'll stay hot.
It's not to worry about though, in most cases. At a higher level, bspec can handle being heated up for several laps without it necessarily making him do poorly.
For example, in drafting races... there's absolutely no way to cool down your bspec. He has to stay with the pack, unless you give him a majorly overpowered car to pull out ahead under its own power. Not possible in stock car (nascar), I think.