My 2 cents: 216 or any splash oiled motor, Pull the pan. Not hard and lets you see inside. Valve cover gets pulled any way to see if all is well up top. This is for peace of mind. I do drain what ever is in there to start with. If I see a lot of sludge in the pan and on the head, it is a good time to turn by hand if you can, and clean what you can. Old paraffin based oils I think are the reason for the sludge. Diesel fuel is a good solvent for this task. Detergent oil like modern oils cause no harm. If the crud in there comes loose it won't matter why it came loose it will do what it does. Never any good. I have put the pan back on after cleaning and with a new filter in place you can fill with diesel and turn the pump with a drill. You can see if the rockers get oil and if it will make any pressure. The engine is not turning so the risk of crud causing damage is very low. The same applies to insert bearing engines. Sludge in some more modern engines is a concern. Any oil that has set for a long time, has water in with it. It becomes very corrosive over time. I have no good thoughts on letting that stuff stay in there. So there you have it. Old or new. Get the big stuff out and then let the modern detergent do what it does. Any other ideas are welcome.
