it sounds like your head is just a bit dirtier then others. You can use this stuff called Gunk(that truely what it is called) I got it at pep boys. You put it in 5 minutes before you change the oil and let it run for five minutes. It helps loosen the nasty petrolium crap and varnishes that build up if you are using conventional oil. I used this stuff when i used to have my 97 Civic ex and when i drained the oil it came out in two colors. One was the normal oil after 3000 miles color and the other was this nasty black color. It seemed to clear alot of crap out. This stuff might help you