Oil types

what types of oil are for certain cars? I have been putting Mobil1 10W30 in my Nissan Maxima but am wondering what the difference is between that and 5w30 and what might happen if I use the wrong type.

the "W" in 5w30 and 10w30 stands for "winter". This basically means that when the temperature of the oil drops below 20 degrees F or so, 5w30 oil will have the viscosity of 5, this helps the oil pump easier in cold weather. One the engine warms up, thats when the "30" kicks in, the oil thickens up to a 30 weight. Same goes for 10w30 oil, except the oil thins to a 10 weight in the cold.

If you haven't experienced any problems with 10w30 oil then there is no need to switch types of oil. However, if the weather gets cold and you experience some hard starting, then 5w30 is better to use.