I have a 1988 Ford Ranger XLT. The truck tends to overheat. I need a new radiator cap because it is leaking from under the cap. The overflow does not have a cap and it has been bubbling up and over flowing. I have it filled up half way. I also lost heat in the cab. First, does the overflow require a cap? Second, could this all be caused due to my thermostat or the water pump? I don't think it is my heater core because it isn't leaking under my dash. The radiator is 3 years old and all hoses are new. Any help or suggestions you can give would be greatly appreciated!