overheating

hello, i replaced the heater bypass pipe from the lim to the bracket since it was cracked. now im still overheating but no signs of coolant oil mix. the resavoir fills up, but doesnt return into the enine. also now the car runs ruff at idle, with ck engine light on. does any body else have simmilar issues that can give me some advise? i have no funds to take to mechanic, or buy new/used car. thanks, Dave