1996 Plymouth Voyager

If you're seeing white crud under the oil fill cap, that's usually from condensation due to excessive short trip driving that doesn't allow the engine to reach normal operating temperature. That is one of the most damaging things you can do to an engine. At least once a week, get it warmed up and on the highway for a dozen miles. If it's bad enough, you will even see water droplets fall off if you shake the cap.

Coolant in the oil from a leaking head gasket turns the oil a sludgy light brown if it's bad enough. Antifreeze will melt the thin first layer of metal on engine bearings. You didn't list your engine size. The V-6 engines don't have very much head gasket trouble. Head gaskets problems are more common in the four cylinder engines.

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