Can you help me find the source of this leak.

[Lvl99mounty]

I have a 1999 mercury mountaineer. when i pour water in the radiator it comes right back out. not from the radiator but from behind it beneath near the area where the glove box is. its kind of hard to pin point. i live in a small town and fortunately i can pour half a jug of water in it and make very short trips between home and work, almost 10 minutes so it rarely has time to overheat and i check the reservoir frequently but for some reason it always stays full even though the radiator wont hold water. I know it VERY risky driving like that but for the moment i dont have any other problems with it. i rather know what type of problem im facing before risking a trip to the autoshop and causing a bigger problem before i even get there. also i just had the water pump replaced. could this be a leaky hose? if not what type of damage could it be?

 

[1998Exp]

I have a 1999 mercury mountaineer. when i pour water in the radiator it comes right back out. not from the radiator but from behind it beneath near the area where the glove box is. its kind of hard to pin point.

Below the glove box? This sounds like a heater core leak, and the coolant running out through the A/C condensation tube - which is located on the firewall, about the spot you described. I understand that your system is now holding water, not coolant, but when it still had coolant did you notice a sweet smell in the cabin and/or oily fogging of the windshield? These would be sure signs of a leaking heater core.
PS: you already know it, but driving a vehicle with a massive coolant leak is asking for the engine to seize up. Don't do that if you can't afford a new engine - or a new truck.

 

[Lvl99mounty]

Not directly below it but in that area beneath the vehicle. Its hard to tell where its coming from exactly. Yes i can put water in it but it will flow right out. I tried a few times to pour coolant into but that did the same. No, at the time there was no smell or fogging that i was aware of. there was a gurgling sound from the glove box but that stopped after the water pump was changed.

 

[1998Exp]

Not directly below it but in that area beneath the vehicle. Its hard to tell where its coming from exactly. Yes i can put water in it but it will flow right out. I tried a few times to pour coolant into but that did the same. No, at the time there was no smell or fogging that i was aware of. there was a gurgling sound from the glove box but that stopped after the water pump was changed.

With a massive leak like yours, it should be very easy to spot where it's coming from. A flashlight and bit of crawling under the vehicle will help... You didn't say which engine you have, but the one I am familiar with has nothing but hoses leading to the heater core in that area. So it's either the heater core itself (you will see the water coming out of a little tube poking through the firewall or the floor right next to it) or one of those hoses. More likely the former.
The reason your overflow reservoir stays full is probably because the radiator never builds any pressure. It sucks the fluid from the reservoir when it cools down and the pressure drops. Also, the tube going to the reservoir may be clogged - but this is your minor problem. Good luck!

 

[RandomNerd2000]

My bets are on either heater core or hoses, it'll be blantantly obvious underneath the truck looking up which is the culprit.

 

[lobo411]

1. What engine?

2. Just because the needle doesn't read overheated doesn't mean it's not overheating. The engine temperature sensors work by measuring the coolant temperature. No coolant = no usable data.

 

[RandomNerd2000]

^That, I have a 4.0 SOHC truck I'm 99% sure blew the head gasket unknowingly from air in the system where the PO ignored a thermostat housing too long. The sensors can NOT read steam, the pressure in the system is a MUST for accurate sensor readings I've found.

 

[410Fortune]

a huge leak in that (firewall in engine bay, below heater blower motor) area is either the hoses to the heater core or the heater control valve (plastic vacuum controlled valve)
Heater core leak would be inside the truck

 

[koda2000]

If it's coming out of the same drain tube as the A/C condensation, then it's a hole in the heater core. Big job to change because you basically have to remove the dash to get at the heater core. A temp solution would be to bypass the heater core, of course if you don't replace the core before winter you'll be living w/out heat.

If the source of the leak is from the engine compartment on the passenger side, then it could be a leaking heater hose or heater control valve. These are pretty easy to replace and are inexpensive parts.

If the source of the leak appears to be be coming from the rear of engine it could be a rusted out freeze plug or perhaps a blown head gasket (but in my experience head gaskets don't usually leak so badly that the water will just pour out as quickly as you can pour it in). Have you overheated the engine yet?

 

[Turdle]

Dripping in the passenger side exhaust is usually a heater core. You can temporarily bypass it with a 5/8" double barbed nipple, run the 2 heater hoses going to the firewall into each other.

link and picture for reference only

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For the repair, you better do it yourself, because it is a very expensive repair, known to total an explorer. In fact, my present truck was sitting in the wholesale lot, traded in for this very problem. It is not real "hard" but it is tedious and time consuming.