If you have an airlock, here's something I've done in the past that has worked on a couple of cars. Find a parking ramp with as high an incline as you can get. With the engine hot, turn the heater controls to high, put it in low and go up the inclines as fast as safely as you can. I did it off hours when there was no traffic and went up and down several times and at the end the air had pushed through to the radiator.
Good luck.
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