I have done it with my cars before and they ran better. I usually use the motor flush by Gunk and followed the directions. My grandfather always used a little diesel fuel and ran the engine about 7 minutes at idle. He then would drain and refill the oil and run it 1000 miles and drain it again. I also heard ATF fluid did a good job of cleaning out you engine. My father in law had an old mazda 323 and it started smoking and running poorly. His neighbor told him to put a quart of ATF in place of a quart of oil and run it for about 600 miles. He did it and it solved the problem. That was 5 years ago and he is still driving the car.