I have a 2003 Kia Spectra. Just replaced the radiator. The car does not overheat when running, no fluid leaking. However, car is very sluggish when accelerating. Rpm goes up but car jerks into movement. There is light white smoke once car is fully warmed up. I did not have this problem at all prior to replacing the radiator. I've read in a few places it could be an airlock so I tried running the car with heat on high and cap off radiator. The heater blew hot air as it should but once I replaced the radiator cap and tried driving it's still sluggish. I should mention I have only driven it at lower speeds through the parking lot and not on the highway. Should I drive it at higher speeds for longer distance to remove airlock? I don't want to blow up my engine. Please help.