My car does not reach normal operating.

My car does not reach normal operating temperature while driving. Only if you let it set and idle will it eventually heat up and the fans kick on. I've replaced all kinds of stuff restoring this car including the water pump and thermostat. It's almost like the water is somehow getting by the thermostat maybe bypassed somehow. I don't see any out of place hoses or anything though. Could this possibly be because someone put a different radiator in it?