Does it have a lower radiator hose? Have replaced the upper. Still leaking antifreeze when engine is hot.

This is actually not too difficult.
I recommend replacing the upper, and lower radiator hoses while you are replacing the radiator if they are getting old.
1. Disconnect the battery.
2. Remove radiator fan (Some had two 10mm bolts at the top, and slots at the bottom, others had two more 10mm bolts on the bottom.) - And unplug the electrical connector.
3. Disconnect transmission lines (you will loose a bit of fluid)
You may also have two engine oil cooler lines that need removing (Also may loose some oil)
4. Remove upper and lower radiator hoses, and the overflow jug hose.
5. Unbolt radiator (should have two 8 or 10mm bolts connecting it to the radiator support near the top of the radiator)
6. Pull radiator up and out.
7. Reverse for reassembly
8. Refill radiator, I usually leave the top radiator hose loose while filling to remove air bubbles in the engine. - reconnect upper hose when fluid starts to get close to the radiator inlet. Some of these engines have a small brass air bleeder near the thermostat housing to accomplish this in a different way. Also fill the overflow jug about half way.
9. Check transmission, and engine oil. - Run engine, and watch for any leaks. - Recheck antifreeze just to be sure. Obviously don't open the radiator cap when the engine is hot.

Check this procedure to REMOVAL & INSTALLATION
(1.8L and 1.9L Engines)

CAUTION Never open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant. Also, when draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantities. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.

1. Disconnect the negative battery cable.
2. Place fender covers on the aprons.
3. Raise and safely support the vehicle. Drain the cooling system.
4. Remove the right and left-hand front splash shields.
5. Disconnect the lower radiator hose from the radiator.
6. If equipped with an automatic transaxle, disconnect the lower oil cooler line from the radiator. Remove the oil cooler line brackets from the bottom of the radiator.
7. Lower the vehicle.
8. If equipped with an automatic transaxle and air conditioning, remove the seal located between the radiator and the fan shroud.
9. If equipped with an automatic transaxle, remove the upper oil cooler line from the radiator.
10. If equipped with the 1.8L engine, remove the resonance duct from the radiator mounts.
11. Unplug the cooling fan motor electrical connector and the cooling fan thermoswitch electrical connector.
12. If necessary, remove the cooling fan thermoswitch for clearance.
13. Remove the three fan shroud attaching bolts and remove the shroud assembly by pulling it straight up.
14. On some 1.9L engines equipped with A/C, remove the upper radiator air deflector from the radiator and set it aside.
15. Remove the upper radiator hose and the two upper radiator mounts.
16. If equipped, remove the fluid cooler tube bracket bolts and coolant overflow hose from the radiator.
17. Remove the radiator from the engine compartment by lifting it straight up.

2.0L Engine
(1997 MODELS)

1. Remove the fan motor, blade and shroud assembly.
2. Raise the car and support it with safety stands.
3. Unfasten the left-hand splash shield bolts and remove the shield.

CAUTION Never open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant. Also, when draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantities. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.

1. Drain the cooling system into a suitable container.
2. Disconnect the lower radiator hose and if equipped with an automatic transaxle, the lower oil cooler outlet tube.
3. If equipped with an automatic transaxle, Unfasten the oil cooler tube bracket bolts.
4. Lower the car and disconnect the upper radiator hose.
5. Remove the radiator cap and disconnect the radiator overflow hose.
6. If equipped with an automatic transaxle, disconnect the upper oil cooler outlet tube.
7. Unfasten the four radiator bracket bolts and remove the radiator from the engine compartment.

To install:

1. Install the radiator and tighten the bracket bolts.
2. If equipped with an automatic transaxle, connect the upper oil cooler outlet tube.
3. Install the radiator cap and connect the radiator overflow hose.
4. Connect the upper radiator hose, then raise the car and support it with safety stands.
5. If equipped with an automatic transaxle, tighten the oil cooler tube bracket bolts.
6. Connect the lower radiator hose and if equipped with an automatic transaxle, the lower oil cooler outlet tube.
7. Fill the cooling system with the specified amount and mixture of coolant.
8. Install the splash shield and tighten the bolts.
9. Lower the car and install the shroud, blade and fan motor assembly.
10. Start the car and check for coolant leaks.

Hope helps (remember to rate this asnwer).

TO CHANGE RADIATOR FIRST YOU TURN OFF RADIO FIRST TO KEEP FROM LOSING RADIO CODE.DISCONNECT NEGATIVE BATTERY CABLE.RAISE FRONT OF VECHICLE SUPPORT ON JACK STANDS.REMOVE THE LOWER SPLASH SHIELDS.NOW YOU NEED TO DRAIN THE COOLING SYSTEM.CATCH COOLANT IN A LARGE DRAIN PAN.REUSE COOLANT IF ITS FAIRLY NEW.IF COOLANT VERY OLD CHANGE IT.PUT OLD COOLANT IN SOME EMPTY CONTAINER TAKE TO A GARAGE OR WHOEVER DISPOSE IT.DONT POUR ON GROUND.HARMFUL TO THE ENVIRONMENT.MOVE THE AIR INTAKE DUCT PASSES OVER THE TOP RADIATOR HOSE.NOW WHEN ALL COOLANT DRAIN OUT.LOOSEN UPPER AND LOWER RADIATOR HOSE CLAMPS.THEN DETACH THE RADIATOR HOSES FROM THE FITTINGS.IF THEY ARE STUCK GRASP EACH HOSE NEAR THE END WITH A PAIR OF ADJUSTABLE PLIERS AND TWIST IT TO BREAK THE SEAL THEN PULL IT OFF REMOVE SMALL COOLANT SURGE LINES FROM TOP OF RADIATOR THAT GOES TO THE OVER FLOW RESERVOIR..DISCONNECT COOLING FAN ELECTRICAL CONNECTOR.THEN REMOVE THE COOLING FAN.REMOVE DISCONNECT AUTOMATIC TRANSMISSION COOLER LINES GET READY TO CATCH TRANSMISSION FLUID THEN PLUG LINES. NOW UNSCREW THE FOUR BOLTS TWO ON EACH SIDE OF THE RADIATOR THAT ATTACH RADIATOR TO THE AIR CONDITIONER CONDENSOR CAREFULLY TIP TOP OF THE RADIATOR SLIGHTLY TOWARDS THE ENGINE.REMOVE THE UPPER RADIATOR SEAL AND LIFT RADIATOR FROM THE ENGINE.NOW IS THE TIME TO REPLACE THE UPPER AND LOWER RADIATOR HOSES WITH NEW ONES SINCE ALL COOLANT REMOVE I WOULD REPLACE THERMOSTAT AND RADIATOR PRESSURE CAP.NOW WHEN YOU GET READY TO INSTALL NEW RADIATOR USE SHEETS OF CARD BOARD PROTECT RADIATOR FINS AND CORES FROM DAMAGE WHILE SITTING RADIATOR BACK IN PLACE.ONCE YOU GET UPPER AND LOWER HOSES IN PLACE ALSO PLACE SMALL SURGE HOSES FROM THE OVER FLOW RESERVOIR TO RADIATOR NEW THERMOSTAT AND TRANSMISSION COOLER LINES ALL HOOK UP. START POURING ANTIFREEZE IN THE RADIATOR OR OVERFLOW RESERVOIR IF RADIATOR DONT HAVE RADIATOR CAP ON IT.POUR A FULL GALLON ANTIFREEZE AND A HALF MORE IF LONG AS THE COOLANT STAYS ON THE COLD LEVEL MARK ON OVERFLOW RESERVOIR DONT OVER FILL.IF YOU POUR ANTIFREEZE IN RADIATOR KEEP POURING ANTIFREEZE UNTIL LEVEL STOP DROPPING AND LEVEL OFF AT RADIATOR TOP.START ENGINE CHECK FOR LEAKS. LET ENGINE RUN UNTIL IT WARM UP TOP RADIATOR HOSE GET HOT.WATCH COOLANT LEVEL IN RADIATOR OR COOLANT OVERFLOW RESERVOIR WHEN THERMOSTAT OPENS COOLANT LEVEL WILL DROP.ONCE YOU HAVE ENOUGH COOLANT IN THE SYSTEM COOLANT LEVEL WILL STOP DROPPING.THEN YOU READY TO GO.LET ENGINE SIT A LITTLE WHILE CHECK COOLANT LEVEL AGAIN.COOLANT LEVEL IN THE OVER FLOW RESERVOIR SHOULD BE AT HOT MARK FOR HOT ENGINE AND WHEN ENGINE COLD COOLANT LEVEL SHOULD BE AT THE COLD MARK.IF POUR ANTIFREEZE IN THE RADIATOR COOLANT LEVEL SHOULD BE AT TOP OF RADIATOR BELOW PRESSURE CAP.

First you should drain the antifreez by opening the drain plug located by the lower radiator hose. Then take the upper radiator hose off. Then take the 2 bolts out that hold the housing on. Remove the housng and there is your thermastat. Accordind to VW they want you to put antifreeze on the o-ring I use RTV a little extra help sealing just don't put a lot on. The book says to put thermastat in housing and turn 1/4 turn to right. I'm not sure why but thats what it says. TIP If you close the drain plug now and put as much antifreeze in as you can makes it easyer to get air pockets out later. Mount your therrmostast housing back to block and tighten bolts. Again put as much antifreeze in that you can them put upper radiator hose back on. Again put as much antifreeze in that you can. Now come the hard part sometimes getting all the air out of the cooling system. Put the radiator cap on but loose run the engine till the cooling fan kicks on but keep checking the coolant level. WARNING ANTIFREEZE WILL GET ABOVE 200 DEGREES
both upper and lower radiator hoses should be hot and radiator full. If both hoses aren't hot you have an air pocket that you have to get out. To do this run the engine a couple minutes after the fan kicks on then turn engine off for 5 or 10 minutes and start over keep doing this till both hoses get hot and the air the fan is blowing is hot. Once this is doe yout ready to go. I hose off any antifreeze that got one car so if you see antifreeze under car you know something is leaking and not what was spilled.

BUY YOUR RADIATOR HOSES FIRST MAKE SURE NEW HOSES MATCH THE OLD HOSES. BUY NEW RADIATOR CLAMPS AND HAVE EXTRA GALLON OF ANTIFREEZE. MAKE SURE ENGINE IS COOL IF YOU GOING TO CHANGE TOP RADIATOR HOSE REMOVE RADIATOR CAP OR OVER FLOW JUG CAP IF YOUR RADIATOR DONT HAVE RADIATOR CAP FIND RADIATOR DRAIN PLUG.PLACE A CATCH PAN.OPEN RADIATOR DRAIN PLUG CATCH ANTIFREEZE. DRAIN HALF ANTIFEEZE IF YOU GOING TO REPLACE TOP HOSE AND DRAIN OUT ALL ANTIFREEZE IF YOU GOING TO CHANGE LOWER COOLANT HOSE TO WATER PUMP.WHEN DONE CLOSE DRAIN PLUG.PUT ANTIFREEZE IN A SAFE PLACE FROM PETS AND KIDS UNTIL JOB DONE. WHEN YOU REMOVE COOLANT REMOVE WATER HOSE CLAMPS THEN REMOVE RADIATOR HOSES PUT NEW RADIATOR HOSES AND CLAMPS ON HOSES TIGHTEN HOSE CLAMPS DONT OVER TIGHTEN. POUR ANTIFREEZE IN RADIATOR.CRANK ENGINE UP CHECK FOR LEAKS.CHECK COOLANT LEVEL WHEN THERMOSTAT OPENS ADD MORE COOLANT AS NEEDED.

Nissan Car 350Z & Maxima 1999-06 Radiator - Removal & Installation

1. Before servicing the vehicle, refer to the precautions in the beginning of this section.
2. Drain the cooling system.
3. Remove or disconnect the following:
   Negative battery cable Coolant reservoir tank and bracket Upper mounting bracket Upper radiator hose Oil cooler lines, if equipped Lower radiator hose Cooling fan and condenser fan Fan motors and shields Radiator

To install:

1. Install or connect the following:
   Radiator Fan motors and shields Cooling and condenser fans and torque the bolts to 44 inch lbs. (5 Nm) Lower radiator hose Oil cooler lines, if equipped Upper radiator hose Upper mounting bracket Coolant reservoir tank and bracket and torque the bolt to 44 inch lbs. (5 Nm) Negative battery cable
2. Fill the cooling system to the proper level.
3. Start the vehicle, check for leaks and repair if necessary.

WARNING Do not remove radiator cap when engine is hot. Serious burns could occur from high-pressure engine coolant escaping from radiator. Wrap a thick cloth around the cap. Slowly turn it a quarter of a turn to release built-up pressure. Carefully remove radiator cap by turning it all the way.

1. Before servicing the vehicle, refer to the Precautions section.
2. Drain the cooling system.
3. Remove or disconnect the following:
   Negative battery cable Coolant reservoir tank and bracket Upper mounting bracket Upper radiator hose Oil cooler lines, if equipped Lower radiator hose Cooling fan and condenser fan Fan motors and shields Radiator
   

To install:

1. Install or connect the following:
   Radiator Fan motors and shields Cooling and condenser fans and torque the bolts to 44 inch lbs. (5 Nm) Lower radiator hose Oil cooler lines, if equipped Upper radiator hose Upper mounting bracket Coolant reservoir tank and bracket and torque the bolt to 44 inch lbs. (5 Nm) Negative battery cable


2. Fill the cooling system to the proper level.
3. Start the vehicle, check for leaks and repair if necessary.

WARNING Do not remove radiator cap when engine is hot. Serious burns could occur from high-pressure engine coolant escaping from radiator. Wrap a thick cloth around the cap. Slowly turn it a quarter of a turn to release built-up pressure. Carefully remove radiator cap by turning it all the way.


Fig. Exploded view of radiator and components

1. Before servicing the vehicle, refer to the Precautions section.
2. Drain the cooling system.
3. Remove or disconnect the following:
   CAUTION Do not damage or scratch the A/C condenser and radiator core while removing.
   CAUTION Because A/C condenser is onto the front-lower portion of radiator, moving to rear direction should be at minimum.
   Negative battery cable Engine cover Air duct and air cleaner case assembly Bracket mounting bolt for anchoring A/C piping Reservoir tank and bracket Upper and lower radiator hoses Radiator cooling fan assembly On A/T models, A/T fluid cooler hoses. Plug hoses to avoid leakage Cover, then two A/C condensing mounting bolts located in the upper part of the radiator Rotate two radiator upper mount brackets 90 degrees in the direction shown in the illustration and remove
   
   Fig. Removing A/C condensing mounting bolts
   
   
   
   Fig. Rotating radiator upper mount brackets 90 degrees
   
   
   
   Fig. Removing radiator
   
4. Remove the radiator by performing the following:
   CAUTION Lifting A/C condenser should be minimum to prevent a load to A/C piping.
   With lifting and pulling radiator in a rear direction, disassemble lower mount from radiator core support center. Lift A/C condenser up and remove radiator after disengaging the fitting as front-bottom surface After removing radiator, put A/C condenser on radiator core support center to prevent a load to A/C piping, and temporarily fix it with rope or similar means

To install:

1. To install, reverse removal procedure.
2. Check radiator cap for any leaks.
3. Start and warm up engine. Check for engine coolant leaks and A/T fluid leaks.

Hope this help (remember comment and rated this).

First you have to figure out where it is leaking from.
The usual suspects would be the upper or lower radiator hoses, and after that, the radiator itself.
Hopefully it's a hose, they're usually relatively simple to get at and relatively inexpensive.
However, in order to replace them you will have to at least partially or fully drain the radiator, depending on whether the upper or lower hose is the culprit.
My last leak was from the hose running from the engine block to the heater core.
Let me know what you find, and where.

first check your antifreeze level.

This is how I like to do it. Make sure the car is parked with the front end at an upward angle. Drain the coolant from the petcock at the bottom of the radiator. Remove the upper and lower hoses at the radiator. Remove the thermostat housing, and the heater core hoses at the fire wall. Flush out the radiator by pouring fresh water into the overflow, and the hole where the thermostat was. Flush the heater core as best you can by pouring fresh water into the heater core hose connections.
Let all the water drain out, then button everything back up and replace the thermostat with a new one. Refill the rad and engine by filling the coolant reservoir with a mix of 50% water and 50% antifreeze, or buy the premixed stuff from the auto parts store. (Buy 4 jugs of premix or 2 of straight antifreeze)
Run the engine until it reaches operating temperature and the upper rad hose gets hot. Rev the engine a little to help get the air out of the cooling system. When the thermostat opens, the coolant level will drop in the reservoir, so top it up and replace the cap.
Check for leaks, and check the coolant level for the next few days, and check for leaks.
Dispose of the old coolant responsibly

It should have a lower hose also. Or you could check around the water pump, they have a weep hole on it and they usually leak if the pump is bad.