Hi bro u did mention e46 318i but what model ,n43,n42 ,and what year. common problem to overheat and cause the silinder head gasket to burn,or it may cause of engine oil leaking , before u do anything i sugest u try comprasion test the silinder's to c wheather your piston ring wear or not .check it first ,good luck.
I just recently overhauled my car due to oil leakage, oil in the radiator and the cyclinder start to misfire. As advise by our Sifus here,bring you ride to the workshop and get it checked. Check the head if there`s any leakage as well. Just getting the car overhauled is not tht really bad on the costing. I do forked out about RM2k+ unless you change some other parts also which depends on the parts condition.