Filling a crankcase with automatic transmission fluid, adding a quart of kerosene, using Motor Flush (which is similar to kerosene) are all age-old methods for cleaning out dirty/sludged engines. However, that’s not to say they’re advisable. If you have engine sludge and you use one of these cleaners, you’d better drop the oil pan to clean out the sludge chunks that are now clogging the pickup screen on your oil pump.
If you’ve changed your oil ever 3 months (as you said in your opening post), then I seriously doubt you have any sludge in your engine that you need to worry about.