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Why 3 months? I change mine between 3000 and 3750, but I never follow the 3 month rule. I don't even get close to 1000 miles a month on my Z. Why do they have a 3 month rule?
:newbie: Hi,

This is my first post in this forum (been in it for a while just on the side line). Anyway, the reason for the 3 month rule is because on regualr dyno oil you inevitably get some sulfur with it. Sulfur also come in with the fuel. When you have combustion/high temps in the engine you generate acids (sulfuric mostly from the sulfur impurities and the water generated during combustion). Suppose that you run your car just 1000 miles in one month and keep it (your car) enclosed for another 5 months, you are allowing for those acids to start eating away the cylinder walls and the bearings (mostly small pitting) that can promote premature wear. Now, if you change the oil and don't run the engine at all, you can go longer between changes, but most people, at least I do, run the engine even during the winter just to circulate the oil. This is also another reason why you can go longer with synthetic oils:less sulfur.
Anyway, I have a 2004 black 350z enthusiast and only use mobil1 every 3500 miles with a long purolator filter. Just past the 14k mile mark. I love my Z.

Hope this helps

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