Where is the fan censor located

The cap that holds pressure inside the cooling system -- whether located on the plastic water reservoir or the radiator -- could be bad, even if it looks OK. Buy a cheap replacement online.
Also look for cracks in the rubber overflow line from the radiator to the reservoir -- they often go bad.
If the main water hoses between the engine and radiator haven't been changed, replace them (even if they look good). Many times, when old hoses are removed, they start leaking when they're replaced because the stiff rubber doesn't seal properly -- and your radiator hoses were probably removed when they changed out the water pump.
Also,
--search online forums for your year/model to see if others have same problem.
--if all else fails, drive the car until the engine is good and hot, support the front of the car with jack stands or wheel ramps (NEVER only with a jack), turn on the engine and let it idle. As pressure builds, if there's a leak you should be able to see it dripping. (Don't confuse, though, with condensate dripping from the a/c condenser, which is normal.)

You have a vapour lock. The coolant isn't flowing. The remaining water is not cooling your engine evenly so you could crack your engine block. The water that isn't circulating turns to steam. The water pump could need replacing if the impeller failed. You may need a new thermostat. Get someone knowledgeable enough to fill your radiator properly and then keep the overflow resevoir filled to half. Check that bottle at least every week.

replace thermostat.then bleed coolant system, this is how you do it.fill the cooling coolant system with 50 / 50 dexcool and water to raise boiling point,straight water will evaporate boil away cause engine to overheat catch fire thats why you need 50 / 50 mixture antifreeze and water.to bleed coolant system first fill coolant system until coolant stay at the full cold mark on the the coolant overflow jug,then you start engine allow it to idle,place the heater and ac control in any ac setting except max and the temperature control to the highest setting,run engine until lower hose to water pump is hot. with the engine hot run the engine speed up to 3000 rpm and allow it return to idle, repeat this 5 times. slowly open the bleed valve on the thermostat housing or look for bleed valve at the water pump heater hose.open bleed valve for 15 seconds to expel any trapped air.then top off the coolant as necessary,and when top radiator hose hot thermostat open up.keep adding cooling to overflow until coolant level stop at full cold mark dont over fill coolant.if engine seem like overheating while looking at cooling gauge turn off engine wait a while until cool off add more coolant until coolant level stay stable and dont drop any.when open radiator overflow cap use large rag over the radiator cap to keep from getting scald open radiator cap a little at a time but dont open radiator cap until engine cool down first.replace the radiator overflow cap, thermostat,and engine coolant temperature sensor and check the cooling fans fuses and relays see what happens.

losing a lot of water thru the resevoir overflow tube the only thing I havent done is this sensor. The sensor wouldn't have anything to do with it . Cooling fans like Jeremy mentions or a blown head gasket . A weak radiator cap would also do it ,but you replaced that . your best bet ,take it to a qualified repair shop .

Javier, have you checked the coolant overflow tank for holes, cracks, or loose hose? When the engine in your car heats up, the coolant expands. The coolant overflow tank (located near the radiator) takes up any coolant that is forced out of the radiator. If the tank is damaged or not connected to the radiator correctly, the coolant will not siphon back into the cooling system when the engine cools off.

Both the 4.0L and 4.7L engines use 195� thermostats for all model years from 1999-2004. When replacing a thermostat it is very important to install one with the same temperature rating (the only exception might be with certain performance modifications or chips that recommend or require a different temperature thermostat).

4.0L engine - Draining the cooling system WARNING: DO NOT REMOVE THE CYLINDER BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR DRAINCOCK WITH SYSTEM HOT AND UNDER PRESSURE. SERIOUS BURNS FROM COOLANT CAN OCCUR.

1. DO NOT remove radiator cap first. With engine cold, locate radiator draincock on the right lower side of radiator facing to rear of vehicle.
2. Attach one end of a hose to the draincock. Put the other end into a clean container. Open draincock and drain coolant from radiator. This will empty the coolant reserve/overflow tank. The coolant does not have to be removed from the tank unless the system is being refilled with a fresh mixture. When tank is empty, remove radiator cap and continue draining cooling system. To drain the engine block of coolant, remove the cylinder block drain plug, located on the side of cylinder block below the exhaust manifold.

4.0L engine - refilling the cooling system Coolant recommendations and cautions: The recommended mixture is 50/50 ethylene-glycol and low mineral content water. Never use pure antifreeze. Only Mopar Antifreeze Coolant, 5 Year/100,000 Mile Formula (glycol base coolant with corrosion inhibitors called HOAT) is recommended. This coolant offers the best engine cooling without corrosion when mixed with 50% distilled water. Antifreeze mixture must always be at least 44%, all climates year round. Maximum protection (-90d) is provided with a 68% mixture protection. If the percentage is lower than 44 percent, engine parts may be eroded by cavitation, and cooling system components may be severely damaged by corrosion. CAUTION: Mopar Antifreeze/Coolant, 5 Year/100,000 Mile Formula (MS-9769) may not be mixed with any other type of antifreeze. Mixing of coolants other than specified (non-HOAT or other HOAT), may result in engine damage that may not be covered under the new vehicle warranty, and decreased corrosion protection.

CAUTION: Do not use coolant additives that are claimed to improve engine cooling. 4.0L coolant capacity: 1999-2000: 13.0 qts. (including 2.3 qts. for resevoir) 2001-2004: 15.0 qts. (including 1 qt. for resevoir)

1. Tighten the radiator draincock and the cylinder block drain plug(s) (if removed).
2. Fill system using a 50/50 mixture of ethyleneglycol antifreeze and low mineral content water. Fill radiator to top and install radiator cap. Add sufficient coolant to the reserve/overflow tank to raise level to FULL mark.
3. With heater control unit in the HEAT position, operate engine with radiator cap in place.
4. After engine has reached normal operating temperature, shut engine off and allow it to cool. When engine is cooling down, coolant will be drawn into the radiator from the reserve/overflow tank.
5. Add coolant to reserve/overflow tank as necessary. Only add coolant to the reserve/overflow tank when the engine is cold. Coolant level in a warm engine will be higher due to thermal expansion. To purge the cooling system of all air, this heat up/cool down cycle (adding coolant to cold engine) must be performed three times. Add necessary coolant to raise tank level to the FULL mark after each cool down period.

For more details, you can refer to the Jeep WJ Service Manual Section-07-Cooling-System-Ewj7

Hope helped.

the engine is overheating or u have a defective radiator cap

You would need to check out the different cooling components. The radiator cap, thermostat, fan for radiator (car should run at 195 degrees), is anything blocking the face of the radiator, are any of the cooling hoses kinked or collapsed, is the water pump circulating the coolant, is thw belt still on the water pump?

Yes, there is another one. The one you replaced is the coolant level sensor. The ECT (ENGINE COOLANT TEMP) sensor is located near the thermostat housing. It has a 2 pin plug on it.