why does a car burn oil?
and how do you know when your car is burning oil...

 

when ur piston rings stop sealing the oil seeps by and gets into the combustion chamber and burns up with the gas

 

well if you check your oil level and its goes down over time then you're either leaking oil or burning oil

you'll usually see it as blueish smoke coming from your exhaust, either at start up or under acceleration

 

You can also burn oil if the head gasket gets blown or the valves get bent/worn down so they don't seal correctly.