Transmission fluid works great to flush out the engine. Drain about a quart of the oil out and add a quart of transmission fluid in it. All the detergents in the Transmission fluid should help. You could also try Seafoam, Marvel mystery oil, or Engine Lube or whatever it's called. It comes in a soda can looking bottle. It's silver in color and the logo is a blue diamond IIRC. Run it for a day or so then drain the oil and add a synthetic blend. I would run the synthetic blend after you flush out the engine.


Edit: This is my opinion and solely my opinion. You can try it if you want or try something else. Always remember to do research before you try anything.