I was replying to jeffroj comment that it had fixed the problem. If he didn't have the overheating problem sitting in traffic, I'd agree the problem was fixed.

either way, its definitely a good idea to do this. Also a good idea to fit a front spoiler for track cars - preventing all that air rushing under the front end gets rid of the high pressure area under the engine bay with 2 results:
1) improved cooling - hot air in the engine bay now has a free path to exit under the car AND a greater volume of air is forced to pass through the coolers.
2) reduced front end lift at high speed = better stability and handling on high speed corners

my old L18 powered coupe used to overheat on the track if I took the spoiler off.