Coming up to 3000 miles on my xterra.Wont to change oil and filter at 5000 miles as the owners manual recommends.It has a 4.0liter v6 engine. Nissan recommends 5w30 oil. However the owners manual states that nissan 5w30 ester oil is recommended. My question is can I use say Redline (which is an ester oil but without the API cert which is also a recommendation in the owners maual.)or can i use any of the other well known 5w30 synthetic oils.I do not wont to run afoul of the owners manual and then have a problem and have them void the warranty.The nissan 5w30 eater oil is about 15.00 a quart! yeah I know $$$. I also plan on using a nissan filter as well. thanks in advance. I wont to keep this vehicle for at least 10 years. Right now I am thinking maybe amsoil as it still would be cheaper than the nissan oil. thanks again for the help. new to the forum.