Last time I changed my oil i poured the old oil into the empty jugs after I filled the motor up and only got 13 quarts back, changed it today and only got 12q back. I check my oil monthly and it is always on the full mark. I'm h&s and tb exhaust, wtf is going on? When I change my oil i pull the drain plug and while it's draining I remove the old oil filter and let it drain until it's a slow drip, the motor took all 15q to put it back to the full mark, I pulled the bottom cac boot off and no oil in there. Ideas?