93 Geo metro overheating

I have a Metro with the 3 cyl. engine. It started overheating about two months ago. I replaced the thermostat, both temperature sensors, tested the fan switch (which worked), flushed the radiator and refilled it. Now, it will run fine around town about 5-10 miles and then the overflow tank will boil over and then because there is not enough coolant in the radiator it will overheat. I use a 50/50 mix. I have run the heater at full blast for miles and then stop and open (carefully) the radiator cap. When I rev the motor the level of the coolant rises in the radiator. HELP, I don’t know how to stop it from overheating. Previous to this I bought the car two years ago with a new motor and it had run perfectly until this started happening. Thanks, Dave

Take a good look at the radiator. Are any of the cooling fins missing or look like dead leaves?

But what you can’t see is what’s happening on the inside. If the this old radiator has restricted cores where enough coolant can’t pass through to rmove the heat from the engine when it requires it, the engine will overheat.

The quickest way to determine if it’s a radiator problem is, point an infra-red thermal gun across the radiator cores as the engine begins to come up to operating temp. Those cores that are restricted will show a much lower temp than the cores that have full coolant flow.