Do I have to remove the fan first from thermal fan clutch before removing? Also, where exactly is the water pump located, and how do I remove and replace from my 2000 Astro Van.

just did one today on my shop truck so its fresh in mind , 1st block under wheels so vehicle cant roll over you , then carefully drain the coolant (it might be hot!!) from drain plug next to bottom outlet to radiator hose into a large pan (save it ) locate top hose connection and remove it (one end only) then when coolant stops flowing out , remove one end of bottom hose , if equipped remove the auto trans cooler lines in middle of radiator too , cap them off to save fluid !! when its all unhooked remove holddown bolts from radiator (4) and remove it from vehicle some addl unhooking of fan shroud might be needed to do this , locate fan clutch (if equipped ) and using a band wrench , unscrew it , (left hand thread) that means turn it left to right remove fan and clutch/ drive belt pulley as an assembly , locate /remove water pump holddown bolts , there should be several of them (truck had 10) note the lengths of each bolt (different) as you;ll need to reinstall them exactly as you take em out when all out using a rubber mallet give the pump shaft a sharp blow, this will break the seal of gasket and if got all the bolts out pump will come off engines front ,remove it , clean all the old gasket from the engine face (don't get gasket pieces in coolant passages) install new gasket onto new pump and reinstall to engine , use new same length bolts if old ones look too nasty !! use same thread/ length bolts or you could damage engine block!!! torque the bolts to 19 to 25 inch pounds !! reinstall fan and clutch right to left this time , give the fan one tap with rubber mallet to seat it after contact , reinstall radiator and reconnect hoses (trans too), skim off any non coolant looking stuff from you pan with paper towels an refill the radiator with it , top off with fresh coolant to level , start engine and allow it to come to normal temp (20 minutes) look for any leaks or forgotten bolt holes , this is a simplified version of how to change a rear wheel drive or 4 wheel drive car/lite truck water pump , your exact details maybe different than these

I don't have experiance with this exact model, but all the bolted on fan blades that I have removed f required removal of the belt; then remove four bolts on the front of the fan located in the center of the fan blade

Thermostat...



Fig. The location of the thermostat and its housing on the 3.7L engine


Water Pump...

1. Remove or disconnect the following:
   Negative battery cable Fan and clutch assembly from the pump Fan shroud and fan assembly. If you-re reusing the fan clutch, keep it upright to avoid silicone fluid loss! Lower hose Water pump (8 bolts)
2. Installation is the reverse of removal. Tighten the bolts, in sequence, to 40 ft. lbs. (54 Nm).
   
   
   

   Fig. Water pump tightening sequence-3.7L engine
   

I hope helps (remember to rate this answer).

Engine Fan REMOVAL & INSTALLATION 3.8L Engines

1. Disconnect the negative battery cable.
2. Remove the radiator upper sight shield.
3. Disengage the electrical connector, then remove the integrated relay control/constant control relay module assembly located on the radiator support.
4. Disconnect the fan electrical connector. Fig. 1: Disengage the fan electrical connector
   
   
5. If necessary, remove the air bag crash sensor.
6. Unbolt the fan/shroud assembly from the radiator and remove. Fig. 2: Unbolt the fan assembly from the radiator
   Fig. 3: Remove the fan from the engine
   Fig. 4: Slide the fan as an assembly up and away from the radiator. Be careful not to dislodge the mounting stud on the left side.
   
   
7. Remove the retainer and the fan from the motor shaft and unbolt the fan motor from the shroud.
8. Installation is the reverse of the removal procedures. Tighten the fan shroud retaining bolt to 23–33 inch lbs. (2.6–3.7 Nm). Tighten the fan shroud retaining nut to 71–106 inch lbs. (8–12 Nm). Fig. 5: Constant control relay module location — 3.8L engines
   

4.6L Engine

1. Loosen the fan clutch-mounting shaft from the water pump hub.
2. Loosen the fan shroud from its radiator mounting and remove the lower hose from the shroud.
3. Lift the fan and clutch assembly and the fan shroud from the vehicle.
4. If necessary, remove the fan-to-fan clutch retaining bolts and separate the fan from the fan clutch. CAUTION
   Closely examine the fan for cracks or separation, to avoid the possibility of personal injury or vehicle damage. To install:
   
5. Assemble the fan and fan clutch. Tighten the retaining bolts to 15–20 ft. lbs. (20–27 Nm).
6. Install the fan and clutch assembly and the fan shroud. Mount the fan clutch shaft to the water pump hub and tighten to 37–46 ft. lbs. (50–62 Nm).
7. Slip the shroud into the lower mounting clips and install the shroud retaining screws. Fig. 6: Fan and fan clutch assembly — 4.6L engine
   

5.0L Engines

1. Loosen the fan clutch-to-water pump hub retaining bolts.
2. If necessary, remove the drive belt from the water pump pulley.
3. Remove the fan shroud upper retaining screws. Lift the shroud to disengage it from the lower retaining clips.
4. Remove the fan clutch-to-water pump hub bolts and remove the fan and clutch assembly and the fan shroud.
5. If necessary, remove the fan-to-fan clutch retaining bolts and separate the fan from the fan clutch. CAUTION
   Closely examine the fan for cracks or separation, to avoid the possibility of personal injury or vehicle damage. To install:
   
6. Assemble the fan and fan clutch. Tighten the retaining bolts evenly and alternately to 12–18 ft. lbs. (16–24 Nm).
7. Install the fan and clutch assembly and the fan shroud.
8. Install the fan clutch-to-water pump hub bolts.
9. Slip the shroud into the lower mounting clips and install the shroud retaining screws.
10. If removed, install the water pump drive pulley and adjust the belt tension; refer to Section 1.
11. Tighten the fan clutch-to-water pump hub bolts evenly and alternately to 15–22 ft. lbs. (20–27 Nm). Recheck the belt tension.

It is likely your fan clutch has gone bad and needs to be replaced.
Fan clutches are engineered to improve the vehicle’s cooling system efficiency. The clutch engages the fan at low speeds when additional cooling is needed. At high speeds the clutch disengages the fan, removing the load against the engine and allowing the engine to run more efficiently.
There are two types of fan clutches, non-thermal and thermal. Non-thermal fan clutches engage the fan based on the shaft speed of the water pump. Thermal fan clutches engage the fan based on a bi-metal thermostatic coil, which senses the under hood temperature.

It will look like this...

Locate water pump.. It's where the bottom radiator hose goes from the radiator. Remove any brackets or parts that are in your way. Remove water pump! Reverse procedure for installation. You have to remove the fan clutch from the water pump shaft and lift the shroud, fan and clutch all out together. remove two bolts in the center radiator support which let the radiator move forward an inch or so, loosen the fan from the clutch for a little more wiggle room to get it out. The shroud will have rubber splash shields hooked to the lower sides too, so be sure to unhook them or you will tear out the holes in the rubber shields.The fan clutch has to come off anyway because it's attached to the water pump. You don't need to remove the fan shroud. Just take out two bolts on the fan clutch and loosen the other two so you can push the clutch back a little (DON'T let the fan clutch fall). Then remove the water pump. It's a little tight, but much easier than removing the fan shroud.the only specialty tool that you will need is the water pumpt "grab" tool and the fan clutch wrench. These two items come together in one kit that you can rent from the Auto Parts store.
The "grab" tool holds the water pumpt pully firmly while you rotate the fan clutch retainer using the fan clutch wrench.

DO NOT attempt to use a break over bar or some other home-grown tool to hold the water pump pully while attempting to break the fan clutch free - you will mess up the heads of the four retainer bolts holding the pully to the water pump face. this will help.thanks.

The text below is from the GM Service manual 4.3L V6 Engine
Water Pump Replacement (4.3L)
Removal Procedure
Drain the cooling system. Refer to Draining and Filling Cooling System .
Loosen the water pump pulley bolts.
Remove the cooling fan and clutch assembly.

Tools Required
J 46406 Fan Clutch Wrench

Removal Procedure
Remove the upper fan shroud.
Remove the fan clutch from the water pump in a counterclockwise direction using the J 46406 .
Remove the fan clutch assembly.
Remove the drive belt. Refer to Drive Belt Replacement Remove the water pump pulley mounting bolts.
Remove the water pump pulley.
Remove the radiator outlet hose clamp from the water pump.
Remove radiator outlet hose from the water pump.
Remove the water pump mounting bolts.
Remove the water pump from the engine.
Remove the water pump gaskets.
Clean the water pump gasket mating surfaces.
Installation Procedure
Install the water pump gaskets.
Install the water pump to the engine.
Apply a sealer (GM P/N 12346004) to the bolt threads.
Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
Install the water pump mounting bolts.
Tighten
Tighten the mounting bolts to 41 N·m (30 lb ft).
Install the radiator outlet hose to the water pump.
Install the water pump pulley.
Install the water pump pulley bolts.
Tighten
Tighten the water pump pulley bolts to 25 N·m (18 lb ft).
Install the drive belt. Refer to Drive Belt Replacement in Engine Mechanical - 4.3L.
Install the fan clutch assembly.
Fill the radiator cooling system. Refer to Draining and Filling Cooling System .
Inspect the cooling system for leaks.

drain engine coolant.relieve belt tension .and remove the drive belt.remove upper fan shroud.remove fan or fan and clutch assembly.remove water pump pulley and coolant hoses from water pump.remove water pump bolts.then remove pump from engine.pay attention to bolts location because they are different lenghts.clean water pump gasket mounting surface dont scratch .or pump gasket wont seal and leak .apply sealant to water pump bolts.install water pump with new gasket.if gasket paper put a sealant on it.torque water pump bolts to 30 ft lbs.if you got a 2.2L engine torque water pump bolts to 18 ft lbs.install coolant hoses on pump .install water pump pulley.install fan and fan clutch assembly.install the drive belt .and the upper fan shroud.fill the radiator with coolant.then run engine to check for leaks.WARNING AS A SAFETY PRECAUTION REMOVE NEGATIVE BATTERY CABLE SO CAR WONT BE CRANK BY ACCIDENT. ALSOOOO DONT FORGET TO TURN OFF RADIO FIRST BEFORE DISCONNECTING BATTERY SO YOU WONT LOSE YOUR RADIO CODE.

4.9L SFI
SPECIAL SERVICE TOOL(S) REQUIRED Description Tool Number Fan Clutch Holding Tool T84T-6312-C Fan Clutch Nut Wrench T93T-6312-B
Removal

1. CAUTION: The large clutch assembly nut has a right-hand thread and must be rotated counterclockwise to remove it.
   Remove the fan clutch (8A616) from the water pump (8501) by turning the large nut, which is part of the fan clutch, using Fan Clutch Holding Tool T84T-6312-C and Fan Clutch Nut Wrench T93T-6312-B.
   

1. Remove two screws retaining fan shroud.
   

1. Remove the fan blade (8600), fan clutch and shroud.
   

1. If the fan blade and fan clutch have to be separated, remove the remaining bolts attaching the fan blade to the fan clutch
   

5.0L, 5.8L and 7.5L Engines
Removal

1. Remove screws retaining fan shroud (8146) to radiator (8005).
   

1. Remove four screws retaining clutch on water pump hub.
   

1. Pull fan clutch and fan blade off water pump pilot and remove fan clutch, fan blade and shroud from vehicle.
   

1. Remove four screws and separate fan clutch from fan blade.
   

Item Part Number Description 1 8509 Water Pump Pulley 2 57632-S Screw and Washer Assembly, 5/16-18 x .62 Hex 3 8600 Fan Blade (5.0 and 5.8L) 4 8600 Fan Blade (7.5L) 5 8A616 Fan Clutch 6 380288-S2 Screw and Washer Assembly, 5/16-24 x .88 Hex A — 16-24 Nm (12-18 Lb-Ft)

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This IS EXACT Procedure Bu The BOOK
REMOVAL

1. Drain cooling system.
2. Loosen fan clutch attaching bolts.
3. Remove fan shroud attaching bolts and remove shroud and fan.
4. Remove drive belt.
5. Disconnect lower radiator hose, heater hose and bypass hose from water pump.
6. Remove fan, spacer, water pump pulley and fan shroud.
7. Remove A/C compressor/power steering pump bracket and accessories to clear water pump stud bolt.
8. Remove water pump attaching bolts and the water pump.

INSTALLATION

1. Reverse procedure to install. Tighten water pump retaining bolts to 12-18 ft. lbs.

NOTE: All water pumps have a sealed bearing integral with the water pump shaft. The bearing requires no lubrication. A bleed hole in the pump housing allows water that may leak past the seal to be thrown out by the slinger. This is not a lubrication hole. If the pump is damaged and requires repair, replace it with a new pump or a rebuilt one.
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