What is the best way to tell if your water pump is not working, if there is not leaks apparent?

Stop leaks as you describe are oil based and it wouldn't be a good idea to add it to a water-based cooling system. Because water is present there is no guarantee the substance would have the intimate contact with the rubber seal it would need to work - if indeed the water pump has a rubber seal.
Older water pumps could have a carbon seal or a gland seal.

Reconditioning the water pump or replacing it seems the best solution.

It is the water pump, i would buy a new thermostat also, you can buy a water pump that comes with a new stat and housing, that is the best way i think and that is the way i do them.

These water pumps are big looking but are very easy to replace, i will tell you that when they leak it is very, very hard to see the weep hole, the area you say yours is leaking is the pump so sure, this waterpumps leak at the mating gasket where the pump meets the block or weep hole, any way it is the waterpump.

you will see the new one , how they put the weep hole it flows through the housing to leak out when bad but hard to see.

hope this is helpful.

Check for water laying in the heater core box.Most likely the heater core is leaking.

If it's leaking that bad, open the hood take off radiator cap and fill with water (without making a mess and spilling a bunch. Then simply watch for where the leak is at, if it's leaking from a hose, the radiator, or from around the area where the belt is located on the passenger side of the engine compartment. If it's leaking from the passenger side around the belt area your water pump is the most common cause. They are made so when the bearing wears out around the shaft the pulley bolts, it has what are called weep holes and the water just runs out to tell you to replace the water pump.

sometimes it makes noise But uselley you can tell by leaking and the owner's manual always tells yout to replace it around 60.000 to 90.000 that means when you are changing the timing belt as well.

Temporarily.... but products like stop leak can also block your in-car heater matrix. They are temporary get-you-home measures. yes, it may work, but at the end of the day if the water pump leaks the best solution is to fit a new one.

You will have to see it. There are dentist type mirrors available in auto parts strore that will allow for you to see it, PLEASE do this when the engine is relatively cool. e.g. start-up. The coolant generally travels straight down, although this is not always the case it is a good indication as to the locatioon of the leak. It is impossible for the coolant to leak from between the block and pan. It appears so as the coolant travels along the rim of the oil pan on its way to the ground. If you can get a thin cardboard strips in there you can tell where the wet starts and stops

Check your bottle cap, ensure that cap is tight. If it is, replace cap. Cap is not holding pressure.

0k moon wizard, is the water pump leaking? There is a 'weep hole' under the pump. When it is on the way out (needs replacement) it will start to leak antifreeze there, and it will get worse. If u can get a small mirror and look under the center of the pump, it would be obvious if it was leaking or not. If the pump is going bad, u will see the leak, or evidence of it (corrosion, an obvious path of the leak, actual antifreeze leaking. If the pump isn't leaking or making a lot of noise (bearings shot), then it's not the water pump. There is antifreeze manufactured now that will work in GM (dex cool) vehicles and all others (the green stuff). If u don't see an actual leak, the thermostat was installed properly, the gauge shows it's in the normal zone, I'd have the temp sending unit checked since it's apparently not working properly, and that leaves the radiator. It probably is the problem, it could be plugged up w/ rust and corrosion, which would diminish the cooling ability. Let me know what u find. countrycurt0