My only experiance involves a borrowed econ-line van. By brothe-in-law had been talked into "cleaning the sludge" out of the engine. Later, about 1000 miles from home, a bit of sludge broke loose, clogged an oil passage, and seized a valve. Big mess. I never use detergent unless it has been used continuosly from when the engine was new.
For situations like that, I'd get something like Berryman B12 Chem-Tool and follow the directions on the can. Basically dump it in, run the engine for a few minutes, then change the oil. Should clean a lot of that crap out, then it should be safe for detergent oil to keep it clean.
