Why engine oil passes to the coolant container making a mixed liquid? Its a ford econoline 2006 van?

Why engine oil passes to the coolant container making a mixed liquid? Its a ford econoline 2006 van? - 1

First guess would be a leaking head gasket. Check the engine oil & see if there's coolant in it…

Only two possibilities, well 2 and a half. The head gasket has failed, or head is cracked, effectively the same thing, or the oil cooler if fitted has failed.

Engine oil then head gasket problem. Transmission fluid then the transmission cooler on the side of the radiator has a hole in it and mixing anti freeze and transmission fluid

Some seepage of oil into the cooling system is to be expected in an older motor. The head gaskets start to leak little.
Take the radiator cap off and run the motor to see if you have any air pockets in the cooling system. Top up the coolant if air comes out. If you have pressure in the cooling system with the radiator cap off and a geyser of coolant coming out of the radiator neck it's time to replace the head gaskets.

Bad head gasket or cracked cylinder head is allowing oil to migrate into the cooling system.