Dont tell the insurers you drove it after the accident to over heat it???? theres an option they would not be any the wiser and would not even think to question it. If you left the engine running for a short while after the crash it could have overheated then without you even realising. Not trying to be dishonest but they sure as hell would not pay out if you modified it, even slightly, without telling them!!!

Having worked in insurance for over 10 years one thing I know is that less information is best. You smashed your car up, your fault, please come fix it. Upto them then to determine the damage and what caused it. 9 times out of 10 they dont question as it costs too much time and money to do so.