1988 Dodge Caravan smoke

Does this happen when you first start the car only?

Usually, valve seals allow oil to drain into the cylender when the engine is off. I wonder if the drain plugs are clogged in the head and causing the head to hold too much oil. Have you ever taken the valve covers off?

Usually valve guide seals will only cause the smoke when the engine is first started, or it can happen under full accelleration. Since yours only happens when the engine is warm, I have a feeling the ports in the cylender head are partially plugged and cauising oil to drain back the oil pan slowly. As a result, there is a build up of oil in the head causing the smoke.

Have you ever removed the valve cover?