Agreed! You could also use Diesel, ATF... pretty much any type of a detergent. Run it for 10-15 minutes, then dump the oil. Don't change the filter yet. Then fill with 3 qts of cheap dino-oil and a quart of ATF/Diesel/Seafoam/whatever and do it again. Then drain it again. You can repeat as many times as you like or until it comes out relatively clean, and then change the filter. You'll be surprised how nasty that "10 minute old oil" can be!
Then use some regular 10w30 or 10w40 and see if it makes any difference. But i'd plan on a rebuild, replacement motor, or new car sometime in the near future if you're burning that much oil. I have run regular 10w40 in my car since I got it a few years ago with no issues at all on the heavier oil. 255k and doesn't smoke, leak, or burn a drop of oil. Then again I live in GA where it almost never gets very cold, so the thicker oil doesn't hurt anything in the winter. And if it's cold, I just don't leave the house. It snowed this winter, like 6 inches of snow! First time we have had snow on the ground since 1987. The 4wheelers got a LOT of use but my car didn't move for about 3 or 4 days until it all melted away lol