We replaced the water pump and radiator - leaking coolant

A worn water pump is the most likely. If the coolant is going down, the water is going somewhere.

The most common reasons an Oldsmobile Alero is overheating are a coolant leak (water pump, radiator, hose etc.), the radiator fan, or a failed thermostat. Coolant leak (water pump, radiator, hose etc.)

Oldsmobile Alero Overheating - RepairPal

Videos on overheating. You probably have air in the system from when you replaced the thermostat. The coolant system needs 'burping' of air.

https://www.google.com/search?q=2000+Oldsmobile+Alero+running+ho

Burping

https://www.google.com/search?q=burping+coolant+system

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then replace it

I would check the vanes on the water pump and the inside of the radiator. Both can cause this.

SOUND LIKE HEAT CORES LEAKING ANTIFREEZE INSIDE DASH.

CHECK AROUND WATER PUMP AREA.AND THERMOSTAT HOUSING FOR LEAKS.THE MECHANIC WHO PUT THE WATER PUMP ON MAY FORGOT TO PUT SEALANT ON BOTH SIDES OF THE WATER PUMP GASKET CAUSING LEAKS.LOOK AROUND THERMOSTAT HOUSING FOR LEAKING.IF THERMOSTAT SEAL WAS DAMAGE DURING INSTALLATION IT WILL CAUSE LEAKING.IF ALL LOOKS GOOD CHECK FOR COOLANT LEAKS AROUND RADIATOR .CHECK RADIATOR TOP AND BOTTOM HOSES FOR LEAKS AND CHECK HEATER PIPES AND HEATER CORES HOSES FOR LEAKS.IF ALL HOSES GOOD.CHECK FOR LEAKING CORE PLUGS.

ouch. leaking fluid and no signs of leak. check engine oil. if it appears milky, you are leaking into the cylinders. this means you'll need a new head gasket.

Sometimes the pipe that runs under the intake will leak. Can you smell antifreeze burning while you are driving? Another way to tell, is to let the vehicle run with the cap off. IF you get alot of bubbles out of the radiator, you have a cracked head, or a bad head gasket which is also a fairly common problem. It will push the antifreeze out of the radiator, and cause it to overheat.

the leak may be a water pump. the fan only comes on when the ac is used or the temp passes a pre determined number. so with no ac the fan will run once in a while....not always......

Your radiator efficiency has been reduced by (what is called) blossoming. Blossoming is electrolytic growth of crystals inside radiator duct passages. This typically occurs in the older Troops as gradual overheating probs cause the vehicle to run low on coolant, then water is being used to top off system repeatedly, acid levels in cooling system rise as the coolant protectants degrade and the inside of the radiator ducts 'blossom' with small crystalline growths that reduce the radiators flow and ability to cool the engine. Flushing and blowing out the radiator are temporary fixes. Replacing the radiator is the permanent fix. You did the right thing by replacing the water pump, tstat and radiator cap. An old, original water pump usually fails soon after the radiator is replaced. New Trooper radiators are fairly cheap, $85+. The replacement can be done by any backyard mechanic or DIYer in under and hour. You know the typical warnings about the toxicity of antifreeze and the deadly affects on pets who drink improperly disposed coolant. Good luck to you. It's an easy remove and replace. Your Trooper will thank you with many cool running miles. -Geoff

You can have it repaired at a radiator shop, or replaced with a new one. Are you sure it's the radiator that's leaking, sometimes it's the water pump or a hose that drips down onto the radiator. It can be difficult to locate due to air circulation of the fan and driving which spreads the leaking fluid around. I assume u top off the coolant often, since u say there are no issues w/ it overheating or running hot. If this is the case, the leak will eventually get worse, and adding coolant constantly gets expensive. Good luck, let me know what u decide to do, or if u have any other questions. Curt