If there is oil getting to the top of the piston and burning then you have a blown head gasket or the piston rings are worn or broken. Engine must be disassembled.
You have to disassemble the entire engine, remove the piston and check the rubber ring around that piston.
Oil rings Combustion rings Piston rod Piston rop cap
Bad piston rings. Get new engine.
The gasoline is avoided to go into the oil by few piston rings placed on the piston of the engine. Actually, the piston rings are made for this purpose only.
Toyota changed piston size in engine. It is shorter and creates wear on piston rings.
worn piston rings
Replacement piston rings.
It is a little nozzle which is pointed towards the beneath of a piston in an internal combustion engine. It is linked to the pressurised side of the oil system, so cool oil coming directly from the oilcooler will spray onto the piston and cooling it instead of just cooling around the cylinder. This enables the engine to run a much more efficient combustion without the chance of melting a piston or overheating the engine which could lead to engine failure.
Worn piston rings. Incorrect weight engine oil. Gasoline mixed with engine oil. Crankcase overfilled with engine oil.
6 ====================================================== My Chilton book shows ( 5 quarts ) with engine oil filter change
You either have an oil leak or the engine is burning oil cause by worn piston rings. If you see blue smoke it is burning oil.