What are the hoses that are located behind the plenum, and go through the firewall on an '03 Montero Sport 3.0L V6? If they are the heater core hoses, what do they attach to at the lower end?

There's is 2 hoses behind the engine connected to heater core disconnect them and connect it together
Any auto part sales heater hose bypass tube

SECTION 412-02: Heating/Defrosting 1998 Explorer/Mountaineer Workshop Manual REMOVAL AND INSTALLATION Heater Core Removal

1. NOTE: If a heater core leak is suspected, the heater core must be leak tested before it is removed from the vehicle. For additional information, refer to Section 412-00 .
   Drain the radiator. For additional information, refer to Section 303-03 .

1. Remove the heater water hoses.
   1. Squeeze the clamps and pull the hoses off.
   1. Disconnect the vacuum hose from the water control valve.

1. Remove the instrument panel. For additional information, refer to Section 501-12 .

1. Remove the A/C evaporator core housing. For additional information, refer to Section 412-03 .

1. Remove the A/C evaporator core housing. For additional information, refer to Section 412-03 .

1. Remove the powertrain control module (PCM). For additional information, refer to Section 303-14 .

1. Remove the PCM heat sink.
   1. Remove the ground strap screw.
   1. Remove the heat sink.

1. Remove the heater air plenum nuts from the engine side of the dash panel.

1. Remove the heater core.
   1. Remove the heater core cover to air plenum screws.
   1. Lift off the cover.

1. Remove the heater core (18476).

Here are the instructions with a diagram. If you need to enlarge the diagram save it to your picture files and then enlarge it there.

1. Disconnect battery ground cable, then drain cooling system. See: Engine, Cooling and Exhaust\Cooling System\Service and Repair

2. Disconnect heater hoses from heater core. Plug heater hoses and core fittings to prevent coolant spillage.

3. Remove bolt located below windshield wiper motor, attaching left end of plenum to dash panel.

4. Remove nut attaching upper left corner of evaporator or heater case to dash panel.
5. Disconnect vacuum control system supply hose from vacuum source, then push grommet and hose into passenger compartment.

6. Remove all instrument panel retaining screws and pull instrument panel back as far as possible without disconnecting any wire harnesses.
7. Loosen right door sill plate and remove side cowl trim panel.

8. Disengage temperature control cable housing from bracket on top of plenum. Disconnect cable from temperature blend door crank arm.

9. On models w/Automatic Temperature Control (ATC) , remove cross body brace and disconnect wiring harness from temperature blend door actuator and disconnect ATC sensor tube from evaporator case connector.
10. Disconnect vacuum harness at vacuum connector near floor air distribution duct.

11. Disconnect white vacuum hose from outside recirculating air door vacuum motor.
12. Remove two hush panels.

13. Remove one plastic push fastener retaining floor air distribution duct to left end of plenum. Remove left screw and loosen right screw on rear face of plenum. Remove floor air distribution duct.

14. Remove two screws from rear side of floor air distribution duct to plenum. To remove right screw, it may be necessary to remove the two screws attaching lower panel door vacuum motor to mounting bracket.

15. Remove push fastener attaching floor air distribution duct to left end of plenum, then remove floor air distribution duct.
16. Remove two nuts located along lower flange of plenum.
17. Carefully move plenum rearward, so that heater core tubes and plenum case upper stud clear openings in dash panel, then remove plenum from vehicle by rotating upper portion of the plenum forward, down and out from under instrument panel. It may be necessary to carefully pull lower edge of instrument panel rearward while plenum is being removed from behind instrument panel.
18. Remove retaining screws from heater core cover, then the cover from plenum assembly.

19. Remove retaining screw from heater core inlet and outlet tube bracket.

Heater core removal and installation diagram.






20. Pull heater core and seal assembly from plenum assembly.
21. Reverse procedure to install.

Section 12-03: Air Conditioning System 1992 Town Car/Crown Victoria/Grand Marquis Workshop Manual REMOVAL AND INSTALLATION Plenum Removal

1. Disconnect battery ground cable.

1. Disconnect the heater hoses from the heater core tubes. Plug the ends of the heater hoses to prevent coolant loss.

1. Plug heater core tubes securely to prevent coolant leakage from heater core during plenum removal.

1. Remove three nuts located below the windshield wiper motor retaining the LH end of the plenum to the dash panel (Fig. 15).

FIG. 15 Plenum and Air Inlet Duct Removal

1. Remove one nut retaining the upper LH corner of the evaporator case to the dash panel.

1. Remove LH and RH lower instrument panel insulators.

1. Disconnect two vacuum supply hoses from vacuum source. Push grommet and vacuum supply hose into passenger compartment.

1. Remove all instrument panel retaining screws and pull the instrument panel back as far as possible without disconnecting any wire harnesses.

1. Loosen the RH door sill plate and remove the RH side cowl trim panel.

1. On manual systems, disengage the temperature control cable housing from the bracket on top of the plenum. Disconnect the cable from the temperature blend door crank arm. On ATC systems, remove cross body brace and disconnect wiring harness from temperature blend door actuator and disconnect the ATC sensor tube from the evaporator case connector.
   

1. Disconnect the vacuum jumper harness at the multiple vacuum connector near the floor air distribution duct.

1. Disconnect the white vacuum hose from the outside-recirculating door vacuum motor.

1. Remove two hush panels.

1. Remove one plastic push fastener retaining the floor air distribution duct to the LH end of the plenum. Remove LH screw and loosen RH screw on the rear face of the plenum (Fig. 14), and remove the floor air distribution duct.

1. Remove two nuts from the two studs along the lower flange of the plenum.

1. Carefully move plenum rearward to allow heater core tubes and the stud at the top of the plenum to clear holes in the dash panel. Remove plenum from vehicle by rotating the top of the plenum forward, down and out from under the instrument panel. Carefully pull lower edge of instrument panel rearward as necessary while rolling the plenum from behind the instrument panel.

Installation

1. Route the vacuum supply hose through the dash panel and seat the grommet in the opening.

1. Position the plenum under the instrument panel with the register duct opening up and the heater core tubes down. Rotate the plenum up behind the instrument panel and position the plenum to the dash panel. Insert the heater core tubes and mounting studs through their respective holes in the dash panel and the evaporator case.

1. Install three nuts on the studs along the lower flange and one on the upper flange of the plenum (Fig. 15).

1. Install three nuts below the windshield wiper motor to attach the LH end of the plenum to the dash panel.

1. Install one nut to retain the upper LH corner of the evaporator case to the dash panel.

1. Position floor air distribution duct on plenum. Install two screws and plastic push fastener.

1. If removed, position panel door vacuum motor to the mounting bracket. Install two retaining screws.

1. Connect the white vacuum hose to the outside-recirculating door vacuum motor.

1. Connect the vacuum jumper harness to the plenum harness at the multiple vacuum connector near the floor air distribution duct. Install floor duct.

1. Connect the ATC sensor tube to the evaporator case connector on ATC equipped vehicles.

1. Install the cross body brace and connect wiring harness to the blend door actuator on ATC equipped vehicles.

1. Connect the temperature control cable housing to the bracket on top of the plenum and connect the temperature control cable to the temperature blend door crank arm. Adjust the temperature cable as outlined under Adjustments.

1. Install the bolt to attach the lower RH end of the instrument panel to the side cowl.

1. Install the RH side cowl trim panel and tighten the RH door sill plate retaining screws.

1. Install glove compartment door and check arms.

1. Connect vacuum supply hose to vacuum supply.

1. Install RH and LH lower instrument panel insulators.

1. Install two hush panels.

1. Unplug the heater core tubes and connect the heater hoses to the heater core tubes.

1. Fill the cooling system with coolant to replace coolant lost during removal of the plenum.

1. Connect the battery ground cable. Check the system for proper operation.

Does it do this all the time or only while running the air conditioner? There are two possibilities. One, when the a/c is running, water condenses on the evaporator and it has to drain out of the box via that hose, this is normal. Two, your heater core is leaking and this is where the water is coming from.

Removal & Installation

Exploded view of the blower motor housing and the heater air plenum assemblies

1. Disconnect the negative battery cable. Allow the engine to cool down. Drain the cooling system to a level below the heater core fittings on the firewall.
   
2. Disconnect the heater hoses from the heater core tubes and plug hoses.
   
3. Remove the five nuts that secure the blower motor housing to the firewall.
   
4. Pull the housing away from the firewall. Disconnect any wire harness plugs which inhibit the housing.
   
5. Remove the remaining nuts which secure the heater air plenum (inside the passenger compartment) to the firewall.
   
6. In the passenger compartment, remove the instrument panel. Refer to Section 10.
   
7. Pull the heater air plenum rearward from the firewall and remove it from the vehicle.
   
8. Remove the heater core from the heater air plenum.
   
9. Inspect all air seals on the components and firewall and replace any that are damaged.
   

1. To install:
2. Install the heater core into the air plenum chamber.
   
3. Position the heater air plenum against the firewall from the passenger compartment.
   
4. Under the hood, install the plenum retaining nuts.
   
5. Install the blower motor housing to the firewall and install the attaching nuts.
   
6. Connect the heater hoses to the heater core tubes at the dash panel in the engine compartment. Do not over-tighten the hose clamps.
   
7. Install the instrument panel.
   
8. Check the coolant level and add coolant as required. Connect the negative battery cable.
   
9. Start the engine and check the system for coolant leaks.
   

If you'll need to remove the intake (or plenum) from the engine there are @ 8-10 No. 12 nuts and or bolts which hold this in place. There are also 1-2 bracket (check by the firewall) you'll need to unbolt too. Be certain to replace the gasket that is found between the plenum and the intake and do not over tighten these nut/bolts only 20ft pounds or so. If you do remove this you'll have to remove the air inlet, throttle cables and remove hoses from the throttle body, some of which carry coolant to properlly preheat the air before enteringthe engine. I have worked on several early 89-93 Monteros without having to remove this for plugs; perhaps different under the hood of the sport.
I hope this may have helped,
Tom

You can bypass the heater core, you just wont have heat anymore. On the firewall of the truck, behind the engine, you will see 2 rubber heater hoses that go into the firewall. They attach to the heater core. Disconnect them and get a plastic connector, and connect the 2 hoses together with clamps to hold them down. This will stop coolant from going into the heater core, and no more leak.

you have to remove the plenum case behind the dash. I will provide 94 gr marquis. don't have 84.



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Section 12-03A: Air Conditioning System—Manual A/C-Heater 1994 Crown Victoria/Grand Marquis. Workshop Manual
REMOVAL AND INSTALLATION Heater Core Removal

1. Remove the heater air plenum chamber assembly as outlined.
2. Heater Air Plenum Chamber Removal
   
   1. Disconnect battery ground cable .
   1. Disconnect the heater water hoses from the heater core tubes. Plug the ends of the heater water hoses to prevent coolant loss.
   1. Plug heater core tubes securely to prevent coolant leakage from heater core during heater air plenum chamber removal.
   1. Remove three nuts located below the windshield wiper motor (17508) retaining the LH end of the heater air plenum chamber to the dash panel .
   1. Remove one nut retaining the upper LH corner of the A/C evaporator core housing to the dash panel .
   1. Remove LH and RH lower instrument panel insulators.
   1. Disconnect two vacuum supply hoses from vacuum source. Push grommet and vacuum supply hose into passenger compartment.
   1. Remove all instrument panel retaining screws and pull the instrument panel back as far as possible without disconnecting any wire harnesses.
   1. Loosen the RH door sill plate and remove the RH side cowl trim panel.
   1. Remove cross body brace and disconnect wiring harness from A/C electronic door actuator motor (19E616) and disconnect the sensor tube from the evaporator case connector.
   1. Disconnect the vacuum jumper harness at the multiple vacuum connector near the heater outlet floor duct.
   1. Disconnect the white vacuum hose from the heater and A/C air inlet duct door vacuum control motor.
   1. Remove two hush panels.
   1. Remove one plastic push fastener retaining the heater outlet floor duct to the LH end of the heater air plenum chamber . Remove LH screw and loosen RH screw on the rear face of the heater air plenum chamber and remove the heater outlet floor duct .
   1. Remove two nuts from the two studs along the lower flange of the heater air plenum chamber .
   1. Carefully move heater air plenum chamber rearward to allow heater core tubes and the stud at the top of the heater air plenum chamber to clear holes in the dash panel. Remove heater air plenum chamber from vehicle by rotating the top of the heater air plenum chamber forward, down and out from under the instrument panel . Carefully pull lower edge of instrument panel rearward as necessary while rolling the heater air plenum chamber from behind the instrument panel .

1. Remove the four retaining screws from the heater core cover (18B300) and remove the heater core cover from the heater air plenum chamber assembly.
   
   Heater Core Removal
   
   
   
   
   
   Item Part Number Description 1 390092-S2 Screw (2 Req'd) 2 18658 Heater Core Case Seal 3 18476 Heater Core 4 18570 Heater Dash Gasket 5 18471 Heater Air Plenum Chamber 6 18B300 Heater Core Cover

1. Pull the heater core assembly from the heater air plenum chamber assembly.

Installation

1. Carefully install heater air plenum chamber assembly into the heater air plenum chamber assembly. Visually check to ensure that core seal is properly positioned.

1. Position the heater core cover and install the four retaining screws.

1. Install the heater air plenum chamber assembly as outlined.

I don't have that old of a shop manual but you usually have to open up the heater plenum case under the dash to acess the heater core. The disconnect fr the heater hoses is under the hood at the fire wall near the passenger side.

1996 version

Heater Core Removal

1. Allow the engine to cool. Observe the safety precautions in Section 03-03 .
   

1. Place a thick cloth over the radiator cap. Turn the cap slowly to its first stop to release system pressure. When the pressure has been released, tighten the radiator cap.
   

1. Disconnect the heater water hoses (18472) from the heater core (18476). Plug the hoses.
   

1. Remove the glove compartment.
   

1. From inside the passenger compartment, remove the seven screws that attach the heater core cover (18B300) to the heater air plenum chamber (18471).
   

1. Disconnect the vacuum source. Leave the A/C plenum vacuum harness (18C581) attached to the heater core cover. Remove the heater core cover.
   

1. Remove the heater core from the heater air plenum chamber.
   

good luck