1994 Ford Aerostar Coolant leak

My 1994 Aerostar sprays coolant all around the side of the engine compartment by the heater fan. No coolant smell in the interior when heater is on though. Happens intermittently (hard to predict), when engine is hot and radiator is full. Is there some kind of high pressure relief valve there? Suspect I filled radiator to top, instead of adding to reservior. Also, temp gauge cycles up and down about a third of it's travel over a period of 20-30 seconds. Is there too much coolant in the radiator, too little? Level is down maybe an inch below top of fins right now, and that is when the coolant gauge cycles.