1999 Dodge Caravan engine smoke from exhaust manifold

Hi, I have a dodge caravan that I've been working on. When I start it up, it runs fine. But after a few minutes, I see white smoke around the exhaust manifold (radiator side). This engine is pretty filthy with oil, grease, and whatever else. So I can only hope that this smoke is a result of the engine just burning up the oil, grease, etc. I thought it might be coming from the spark plugs, but it's not. Does this sound about right? Is the engine just burning up what's on it?

By the way, this van has been sitting for a while. And I recently replaced the timing belt, water pump, and oil pan. I don't know if this could be related to the engine smoke.

Thanks.