Can a warped or cracked head cause an external coolant leak underneath the waterpump and pulley area. I just had the water pump replaced and it is still leaking from the same spot. I was told by an expert that a warped head could compromise the seal on the water pump, but isn't the water pump attached to the block not the head? By the way there is no coolant in the oil, no white smoke out of the exhaust and the engine is running perfect.

Kind of doubtful the water pump is faulty, then. Three ways a water pump is bad: If an internal seal gives way, water will come out the front of the pump and drip down. Or if an internal bearing goes out, the pump pulley will be wobbly or the pump will make a howling noise. The last way and less common is when the internal impellers that push the water get corroded (or rusted if metal) and then they deteriorate to the point they don't push water good enough. This last way is caused by neglect of the coolant system, like not ever changing the coolant for a long, long time.
So if you are over heating without an external leak, or a wobbly, noisy pump pulley, then it is doubtful the pump is at fault. But look at your coolant. If it is very dirty, you might need a new pump. If you are having to add coolant, you need to find the leak, or it could be an internal leak, like into the oil sump.
If not having to add coolant, then you have to check the flow from engine to radiator and back into the engine. Radiators can get blocked, or they can get debris and leaves on the outside and not cool the water well enough. Then if the flow or circulation is good, you need to check for a head gasket leak or a cracked cylinder head.
Good luck.

Check your exhaust pipe when running. Do you see a lot of white smoke? If so, you most likely have a blown head gasket and are losing the water into the cylinders. This will cause overheating with no apparent leaking. If there is no white smoke, then you could be losing water from the "weep hole" under the water pump. This water often hits the engine block and evaporates (causing steam). Once you turn off the engine, the leaking often stops. Look carefully at the underside of the water pump for a small hole where the pulley shaft enters the pump. If you see traces of coolant (or signs that coolant ran down from the hole), you need to replace your water pump.

Water pump is Timing belt driven. It is below the Camshaft sprocket, in the timing case. If you want to repair/replace it here are the instructions.
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COMPONENTS

REMOVAL

1. Using the drain plug, drain the coolant.
2. Remove the drive belt and the engine coolant pump pulley.
3. Remove the timing belt cover, the auto tensioner and idler pulley.
4. Remove the water outlet fitting, the thermostat case and the water pump fitting.
5. Remove the engine coolant pump mounting bolts.

1. Remove the engine coolant pump assembly from the cylinder block.

INSPECTION

1. Check the engine coolant Water pump for cracks, damage or wear, and replace the pump assembly if necessary.
2. Check the bearing for damage, abnormal noise and sluggish rotation and replace the pump assembly if necessary.
3. Check the seal it for leaks and replace the pump assembly if necessary.

INSTALLATION
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1. Clean the gasket surfaces of the engine coolant pump body and the cylinder block.

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1. Install the new engine coolant pump gasket and pump assembly. Tighten the bolts to the specified torque. Tightening torque

Engine coolant pump bolt:
Head mark "7": 17 - 22 Nm(170 - 220 kg.cm, 12 - 16 ft. lbs.)

1. Install the water pump fitting, the thermostat case and the water outlet fitting.
2. Install the auto tensioner and timing belt. Adjust the timing belt tension, then install the timing belt cover.
3. Install the drive belt, coolant pump pulley and then adjust the auto tensioner.
4. Refill the coolant.
5. Run the engine and check for leaks.

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Possibly blew a head gasket allowing combustion gases to enter the cooling system and force coolant out of the overflow tank. This can be verified by doing a compression check on each cylinder.

you should have a block test done. there are different names for it but it requires a special tool that you set over the radiator or reservour cap opening and a special fluid changes colors if exhaust gases are detected in the coolant. this usually signals that you have a warped head or crack in the cylinder head. your car may also have a warped intake manifold. these 3.8 liter intakes warp in the EGR passage area and allow coolant to drain into the crankcase and into your oil pan mixing coolant with the oil. does your oil level seem a little high or is the oil a funny color? btw there are a couple of plastic coolant (elbows) under the alternator area that always leak coolant. you might take a mirror and try to look down there for a leak.

Possible leak areas waterpump, heater core, intake manifold gasket, radiator or hoses. Waterpumps have what they call "weep holes" which is an early warning system to prevent major damage when pump fails. The weep hole needs to be inspected from below and is usual behind waterpump pulley. If it's your heater core, you should smell anti freeze inside truck and in most cases windshield will fog up. Radiator could be pin hole to front side of radiator (which is buried behind AC condenser & grill) and if it was head gasket, intake manifold symptoms would be coolant in oil OR lots of white smoke from exhaust. Try parking it on a clean dry surface and see if you can narrow down area where leak is coming from.

The most likely leak on any engine is the water pump, go under the car and look at the bottom of the water pump are there coolant stains or dips on it?

More than likely the water pump seal has failed. You will have to replace the waterpump to get this fixed. It takes quite a while for water to start circulating due to the thermostat which blocks water from flowing into the radiator when it is still cold (less than 90deg celsius). Due to the overheating the thermostat may also have been damaged and stuck in the closed position. It is not expensive so have it replaced along with the waterpump to be safe. A cracked head will not leak water outside the engine. (In 25 years I've not seen this once)

sounds like the water pump bearing is worn out and has detroyed the water pump shaft seal.
coolant is leaking thru the seal area ,due to the bearing worn out --hence throwing the water pump pulley out of alignment.
The water pump pulley runs of the timing belt.---hence the knocking --either from the pulley or belt chaffing against the timing cover or even throwing the engine timing a few degrees off.
Need to replace water pump and timeing belt and anything else that may be damaged.
That's why, when ever you do a timing belt always do the water pump too.

Did you just do the work and it is over heating or has the work been done for a while? Usually waterpumps get noisy and leak. If work was just done you may have a air lock in cooling system which is making it overheat