Dear brother, the process you did is trying to commit suicide...
Hire someone professional who can look on used engines. We usually buy less mileage engines 5-20k km driven engines.
And head kholne ka Matlab is killing the engine.
And heat issue could be because of leak somewhere in cooling system like radiator or pipes.
And cat con is located between engine head and exhaust, parallel to radiator. Looks like a chimney or cylindrical surface.
This normal gets choked.
And in lahore their are teams who clean up cat con.local mechanics suggest breaking the cat con and they take that broken pieces and sell them for 2-3k per kg. Lol
So my advise is go to catcon cleaning guys.
Search on Google catalytic cleaning in lahore and you'll find teams on it.
If it would be clean they'll say no need to clean sir.