WHY MY CAR ENGINE OIL BECOMES MILKY .

One of the proximate reason is that your car's cylinder head gasket has develop a cracked in it due to overheating or due to the ordinary wear and tear.

 The oil from the oil pan is pumped by the oil pump towards the top of the engine or to the cylinder head. that oil passes thru the cylinder head gasket hole to reach the cylinder head top to deliver oil to the moving camshaft, rocker arm shaft..
the cylinder head gasket has likewise has a hole where the water from the engine block passes to that hole to the cylinder head wall.
If your cylinder head gasket hole for water gets cracked, part of the water will transfer to the hole of the oil on that cylinder head gasket ,  that water now will mix with the oil, making it looks like milk.  Your oil dipstick will show that milky texture of your oil, besides making your oil in your engine becomes too many.