50/50 is ok, its half water half antifreeze. As for your thirsty car, have it checked. it could be a leak but you said it was completely go within 3 days of filling it up. A "leak" is too slow for that. try letting your car run for 20 min.s after u put the antifreeze. let it sit while it runs. Watch to see if and where it leaks or pours out of. Let em know your observations when u bring it to get looked at. If you spilled any onto the engine (headers, manifold, etc.) its going to smoke and give off a smell until it burns off completely.And your air vents will always slightly blow air, it comes from the engine. Plus its an older car- not so "high tech" it's ok too though.