In cold winter climates the systems collect a lot of water along with the oil. You will see a large amount of what looks like chocolate milk. I bought an extra large can since I line in the midwest but haven't logged a lot of winter driving. My results were march to July this year. So the climate actually is part of the differential, also engines are not all the same, driving styles, etc. When buying make sure it is an air/oil separator not just a can. Some forum members have bought cheap ebay cans and then insert stainless steel scrubbing pad into it to turn the can into an air/oil separator. I found this youtube helpful