Howdy all, First time poster. I have a 2011 Nissan Altima 2.5L 26K miles - Mobil 1 Extended Performance 2002 Toyota Camry 2.4L 110K miles - regular oil (I don't know what brand - free oil changes at dealership.) They both are using their recommended oils weights, I am very light on the accelerator and 75% city driving. Should visual inspection of the oil from the dipstick be used as an indicator that it's time to change the oil? Sorry if too much information. Thanks in advance.