You need to have the radiator flushed immediately
Change oil and filter
try using Dawn's detergent
If your husband poured barsleak in the crankcase, it probably stopped up the oil pickup screen. It is supposed to be poured in the radiator. The engine is probably ruined if you have driven it with the oil light on.
Blown headgasket, failed oil cooler, etc.
Do you mean into the engine? If so it depends on how little; a quart is too much for a small engine. There wouldn't be any immediate damage but change the oil before running the car again.
It will do no damage if you just added a little of the wrong weight oil. However if you changed the oil and poured in the wrong weight I would suggest your remove that oil and pour in the correct weight.
It won't hurt it at all .old mechanic's use to pour it through the carburetor to build the litters up
You are screwed! Get that radiator flushed by a profesional ASAP! ANOTHER SUGGESTION DO NOT RUN THE MOTOR HAVE IT TOWED TO A PROFESSIONAL. IF YOU DID RUN THE ENGINE GOODLUCK BUDDY HOPEFULLY IT DIDN'T AFFECT THE ENGINE IF SO YOUR GONNA HAVE A HELL OF A TIME REPLACING ALL THOSE HOSES AND YOUR RADIATOR AND HAVING YOUR COOLANT LINE REPLACED.
Underneath front of motor by radiator. Remove the skid plate .
the engine oil dipstick is right in front of the motor between the motor and radiator, if factory it will have a bright yellow handle that is completely impossible to miss
The most typical reason is a blown head gasket(s).
Oil in the radiator on any vehicle is a sign that there is a blown head gasket. This includes the E46 318i motor. Oil in the radiator is also a sign that the block is cracked. Either way, it is a major issue that needs to be addressed before the engine quits completely.