I checked the oil level before attempting extracting the oil. The dipstick showed full but I am sucking air. I have only managed to remove about 2.5 quarts after an hour last night while the oil was warm and 2 hours this morning with the oil about 50 degrees. I am using a hand pump vacuum extraction device. I pump it ten or so pumps and after a several seconds it starts pulling air out of the oil sump. Does it both when connected with a hose adapter to the dipstick tube and with a tube down the dipstick tube. I had to raise the bow as high as the trailer jack will go just to accomplish what I have. I was sucking only air with the boat level. I have never seen this problem before. I did another 5.0 last week and a 6 cylinder along with 2 Mercruisers the week before that without and issues and the boats sitting level. What could be causing this? If I hadn’t checked the level before I started I would have assumed it had been run out of oil.