"I tryed to change oil in my 87 omc 7.5 litre motor. The problem is I can't get all the oil out. I went thru dipstick tube with vacuum unit that I have used with no problem on other motors. I took between 2 and 3 quarts out, but dipstick still showed normal oil levels. You would think that it would have at least shown low oil on dipstick or clean dipstick with that much oil removed. Manual says it only holds 5 quarts Does anyone know of any other way to remove all oil"