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I would run it with the cap off the radiator. It may overflow on you a couple of times till finally the thermostat is fully open. Once it is fully open and you see water flowing through the radiator, top it off and you should be good. Sounds like you have air in the engine.
If you want to try to prevent this or minimize this in the future, when filling the radiator take one of the heater hoses off the engine, preferably the higher one. Don't take them off the heater core, too easy to crack that. Then fill it till coolant comes out of the place you disconnected, and then quickly reconnect and keep filling. It will still have some air in it but not as much as it does now.