Originally Posted By: mbar1
Originally Posted By: FZ1
It's both! Use the GM spec oil.
What's wrong with the Castrol Edge 0W-40 ?
Seriously,If the car shakes more on heavier than spec oil.....then the oil is too thick for the car. Go back to the oem spec weight.You can go thicker or thinner WITHIN the 30 grade but stay within the mfg. spec oil grade. Hope this helps.