along the same thoughts, with previous question, 2008ford escape 3.0v6, 40k miles, have always used 5w30 synthetic, stay the course, no need to got 5w20, even tho filler cap states that,correct? New 2013 jeep grand cherokee, 3.6 v-6, 5w20 is the recommended, should i allways go with that viscosity? Are newer engine tolerances that tight a switch to 5w30(even synthetic ) would be an issue?Will stay with 7500 mile interval,regardless, synthetic or petroleum, while under warranty time.