This is a mystery to me, I wonder if any kind people here, can help explain whats really going on. This 350 runs perfect, does not smoke or burn oil, the exhaust pipe was coco brown when I bought it. I then changed the oil maybe 4 times in about 2 years 6k miles, try to flush it out. Now it smokes, but only when at idle for extended periods of time. If I start it up and drive it and stop at a traffic light, thats fine it does not smoke. If I start it up in the morning and let it idle for extended period of time it smokes. If on the freeway and run into road construction, then idle for long period of time, after say 5 min, then it starts to smoke. Then road clears up and within a mile or so, no more smoke. Just looking for ideas on what others think is causing it. I think I changed the oil often and knocked sludge loose and blocking the return oil ports. Now it is overflowing into the chambers and burning at idle. Is that even possible? Thinking maybe add some seafoam to the oil and change it again. This motor with a manual transmission is a kick in the pants to drive. Will run 90 mph down the freeway all day long and not burn a drop of oil. Let it idle for 5 min and starts smoking.