ParagonFS

Hi guys i am completely new to this Forum Stuff and need serious help.
my car started mixing oil and water in the coolant reservoir, checked dipstick but no mixing there, nothing in the head either(removed cover on head), mechanic removed the oil cooler and advised that the oil cooler was not the problem but the Gasket for the oil filter housing replaced that and the radiator and did a complete flush. just spent thousands and its still mixing. please advise me. at a point of giving up.