As said its more of an unwritten rule. But I know that at the T & T I was at a few weeks ago atleast half the cars there were street cars and I am sure 99.9% had anti-freeze in them. Sure the track dont want coolant in them but I dont think they will turn half the cars away and loose all that money or take the time police whats in each cars rad. Course they should as they tell me its a bigger pain to clean a coolant spill then an oil spill. Ron