I know it's too late, but when I do the coolant I drain it in to a big plastic tub like thing and then pour it back in to empty gallon water jugs. Then I know how much I have to put back in to get back to where I was (if I drain three and half gallons and only put back three gallons I know I've got an air bubble). Do you have a heater? If so, that can be a trouble spot along with the intake manifold and upper corner of your radiator. Eventually, most bubbles make their way out to the surge tank. Loosening up the heater hose and a fitting on the intake manifold can help, along with parking your car on a big incline (watch your
oil pressure, though
). Do you happen to have a bleed screw, maybe on the top of your radiator? Just keep cracking fittings and clamps and eventually your bubble will work itself out.