I changed the oil on my 95' omc 5.0 (ford) by using the garden hose/transfer pump method. All I could get out of the engine was about 4 quarts of oil. I even raised/lowered the boat to try to get more but to no success. It should hold 6 quarts. I changed the filter and filled it up to the normal level (little over 4 quarts). When I check the oil, it still looks dirty like quite a bit of oil was left in it. Is this normal for this engine? Should I try to drain it again and add more new oil?