In small bowl, combine oil, garlic, salt, pepper and thyme. Rub over surface of roast.
Place roast, fat-side-up, in shallow roasting pan. Insert ovenproof meat thermometer so tip is centered in thickest part of roast, not resting on fat. Do Not Add Water. Do Not Cover.
Roast in a preheated 350°F oven 1¾-2½ hours for medium-rare; 2-3 hours for medium.
Remove roast from oven when meat thermometer registers 135°F for medium-rare or 150°F for medium. Tent with aluminum foil and let stand for 15-20 minutes (temperature will continue to rise about 10°F to reach 145°F for medium-rare; 160°F for medium).
Transfer roast to carving board. Cut into slices.