smells bad

ok sometimes when i rev the engine or have it going fast i can smell something really bad i thought it was maybe oil on the outside of my engine because when i took off the oil filter some dribbled on there so i hosed it off and dried it off with a air hose but still it smelled

then i noticed every time i would open the hood the engine would be really hot but my gauge would say that the engine is running fine

so i checked the oil and it was just a little low so i added another quart and it runs and smells ok now was it getting to low on oil was i burning the oil ??? any body else have this problem?