iMac mid 2011 is too hot to work 🔥 🔥 🔥 High sierra System Software

Hello my iMac will be very hot after three minutes after the start and after 2-3 hours the iMac is so that I have to cool for 1 hour to cool him to continue working I can cool him now with an extra propeller from outside but that's not enough, what can I do about the problem To solves and what is the problem what the iMac 2011 has !!!!!???????

He will sometimes be up to 45 degrees hot I have the heat with a laser measuring device what is too reliable is tested !!!!!