My jetta4 1'8 is mixing water and oil ,I already change top gasket but still mixing, what maybe the causes
You changed the value cover gasket you need to replace the head gasket a much bigger job.
Probably the head gasket or a cracked head or engine block. You need more diagnosis to determine where the water is entering the oil.
Before such serious work, check the oil cooler- ifsthe box above the oil filter with coolant hoses going to it. They can crack internally and cause intermixing.
Looking for a Used Volkswagen in your area?
CarGurus has 103,334 nationwide Volkswagen listings starting at $900.