On blue colour of the fulfilled gases you can draw a conclusion that with your engine not everything is all right even if oil level remains at constant level. Hit of superfluous fuel and a water condensate in oil dilutes it, as a result it loses lubricant properties. It can be observed first of all in the winter, and mainly during short trips when the engine seldom reaches the working temperatures for a long time and the deposit on walls of the chamber of combustion cannot burn down. In such cases you should change oil more often, already after 6000 km of run or time in half a year.