How do you replace the radiator coolant on a 2005 Honda Odyssey

locate the coolant temperature sensor nearto the thermostat housing. Unplug, loosen then plug back up. To bleed, loosen slightly to release trapped air. Once air is relieved, only liquid will come out at this time the air bleeding is done.

Find the leak for the radiator and fix it. Do not drive the car without coolant - you will destroy the engine.

Did you change out the thermostat? I would also change out top and bottom radiator hoses if they feel soft. They should have firm sides.

Drain the radiator by removing the drain plug on the lower right side. If the coolant is fairly new, save it and reuse it. While the radiator is draining, find the code for the car stereo. It should be in with the owner's manual or sales paperwork. (You will need this code later because you are going to disconnect the battery and remove it for access to the thermostat.) Remove the battery. Follow the lower radiator hose to the engine to locate the thermostat housing. Loosen the hose clamp and detach the hose. If it feels stuck, try to twist it first--then pull it off.Remove the thermostat cover bolts and detach the housing cover. If it is stuck, tap it with a soft-face hammer to jar it loose. Be prepared for some additional coolant to spill when the gasket seal is broken. Remove all traces of the old gasket. Install a new rubber seal over the new thermostat and install into the housing. Make sure the jiggle valve is on top and the spring side of the thermostat is directed into the engine. Replace the housing cover and bolt up. Replace the radiator hose. Replace the battery. Refill with coolant. Use the stereo code to get the radio to work.

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Removal & Installation

1. Note the radio security code and station presets.
   
2. Disconnect the negative battery cable.
   
3. Drain the coolant from the radiator, into a suitable container.
   
4. Remove the timing belt. Refer to the Timing Belt replacement in this section for specific details.
   
5. On Odyssey models with the V6 engine, remove the timing belt tensioner. Refer to the Timing Belt replacement in this section for specific details.
   
6. Remove the bolts that attach the pump to the cylinder block.
   
7. If available, locate the two 6.0 mm x 1.0 mm threaded holes opposite from one another on the outer perimeter of the water pump.
   
   • Install by hand, two 6.0mm x 1.0mm bolts at least 1 in. (25mm) long, until resistance is felt.
     
   • Simultaneously turn each bolt one turn at a time until the water pump can be released from the engine block.
     
8. Remove the water pump.
   

Exploded view of the water pump mounting-be sure to replace the O-ring during assembly

If available, use the two 6.0 mm x 1.0 mm threaded holes on the water pump to release the pump from the engine block

Make sure the water pump O-ring is fully seated in the water pump. Using a non hardening gasket sealant will help to hold the seal in place during assembly

To install:

1. Inspect and clean the O-ring mating surface on cylinder block.
   
2. Install a new O-ring on the water pump. Apply a non-hardening gasket sealant between the water pump O-ring and the pump to hold the O-ring in place during assembly.
   
3. Install the water pump onto the cylinder block and tighten the bolts to 106 inch lbs. (12 Nm).
   
4. On Odyssey models with the V6 engine, install the automatic timing belt tensioner, with the tensioner fully retracted using the special tool 14540-P8A-A01 or equivalent. Refer to the Timing Belt replacement in this section for specific details.
   
5. Install the timing belt.
   
6. On 4-cylinder Odyssey models, open the cooling system bleed bolt located on the thermostat housing.
   
7. Set the heater to the full hot position.
   
8. Refill the radiator with a coolant mixture containing 50% antifreeze. Use only antifreeze formulated to prevent the corrosion of aluminum parts. Fill the radiator with the coolant solution.
   
9. On 4-cylinder Odyssey models, fill with coolant until the bleed bolt is free of air bubbles. Then, tighten the bleed bolt to 88 inch lbs. (10 Nm).
   
10. Install the radiator cap loosely.
    
11. Reconnect the negative battery cable.
    
12. Run the engine until the cooling fans cycle two times.
    
13. Turn the engine OFF and top off the cooling system as necessary.
    
14. Install the radiator cap and check for coolant leaks. Be sure the cooling fan turns on.
    
15. Recheck the coolant level and add more if necessary.
    
16. Enter the radio security code.
    

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There is only one drain point. Drain the coolant from the system at the radiator. This will remove coolant from the engine. Be sure and have the heater set to hot. Flush the system with a water hose. Fill the system with a 50/50 mix of antifreeze and distilled water. Do not use tap water. Start the engine with the radiator cap off and keep adding coolant until it will take no more and you see no more air bubbles escaping from the radiator. If there are schrader bleed valves on the engine cooling system use them to remove any more trapped air. Put the cap on and start the engine and let it run for 15 minutes while you check for leaks. I would replace the thermostat at this time as it is just good preventive maintenance.

Lower right or lower left side (between radiator and engine) of the radiator itself.

Follow the lower radiator hose from the radiator up to the thermostat cover. Remove the electrical connector that is on the cover (to the radiator fan switch) and then remove the 2 bolts holding the cover to get to the thermostat.
How to install thermostate:
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. Note the radio security code and station presets.
2. Disconnect the negative battery cable.
3. Drain the engine coolant into a sealable container.
4. Remove the fasteners from the thermostat housing, then remove the thermostat.

To install:
See Figures 1, 2, 3 and 4
Fig. 1: A thermostat can be tested by placing it in a suitable container filled with water, and heating the water with a hot plate while monitoring the temperature with a thermometer Fig. 2: The thermostat should open when the water reaches the correct temperature Fig. 3: The coolant bleed screw is located near the thermostat housing on Odysseys with 4-cylinder engines Fig. 4: Always install the thermostat with the small pin at the top. The rubber thermostat seal is installed around the thermostat

1. Install the thermostat using a new seal. If the thermostat has a small bleed hole, make sure the bleed hole is on the top.
2. Apply an anti-seize compound to the threads of the fasteners.
3. Reassemble in the reverse order of disassembly.
4. Set the heater to the full hot position. Set the heater to the full hot position.
5. On Odyssey models with 4-cylinder engines, locate the coolant bleed valve near the thermostat housing and open the valve 1/2 turn.
6. Top off the cooling system and overflow reservoir with a 50/50 mixture of a recommended antifreeze and water solution, and bleed the system to remove any air pockets as necessary. Simultaneously squeeze the upper and lower radiator hoses to help push any captured air pockets out of the system.
7. Inspect all coolant hoses and fittings to make sure they are properly installed and if previously opened, close the bleed valve.
8. Connect the negative battery cable.
9. Install the radiator cap loosely and start the engine. Allow the engine to run until the cooling fan has cycled two times, then turn the engine OFF and top off the cooling system as necessary.
10. Install the radiator cap and inspect for leaks.
11. Enter the radio security code.

WARNING The manufacturer does not recommend using a coolant concentration of greater than 60% antifreeze. When mixing a 50/50 solution of antifreeze and water, using distilled water may help to keep the cooling system from building up mineral deposits and internal blockage.

This is the original link for more info
http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c152800b0b84
Please let me know if you need more info. I am here to help.
Good Luck

Honda recommends that the cooling system be topped up with coolant four times as part of the refill process. When the engine is fully cold open the radiator cap and add coolant until full. Run the car until fully warm with heater at maximum. Let it completely cool down. Remove radiator cap and top up with coolant. Repeat this process two more times. This helps purge the air out of the nooks and crannies in the cooling system.

-T

The water pump is located along the left side of the engine underneath the plastic covers. You coolant leak is most likely a radiator hose.