5 quarts
The last Plymouth was in 2001. The Chrysler/Dodge 3.3L V6 holds 5 quarts of oil.
Less cheeky answer: 4.5 quarts with an oil filter change, 4.0 quarts without (pg. 186 of 1995 Plymouth Voyager Manual). Try not to overfill; that could aerate your oil and make you lose oil pressure.
Total capacity is 9 quarts
5 quarts
4.5 quarts
4.5 quarts
4.5 quarts
The oil capacity for a 1998 Plymouth Grand Voyager is 4.0quarts (this applies to all engine sizes - 2.4L, 3.0L, 3.3L)
4.5 quarts
5 quarts with filter
5w30 or 10w30