That said, common possibilities include:
* 5W-30: This is a very common viscosity grade for many vehicles, including likely many 1999 Grand Caravans.
* 10W-30: This is another possibility, though less likely to be the *primary* recommendation in a 1999 model.
Crucially: The owner's manual will specify the *type* of oil (conventional, synthetic blend, or full synthetic) and the *API certification* (e.g., SM, SL, SJ - older standards). Using the wrong type or viscosity could damage your engine.
Do not rely solely on online information. Always check your vehicle's documentation for the correct oil specifications.