Secret Coolant Leak

[misterRollsRoycer]

Got a secret-style coolant leak. It's behind the glove box, and what I'm guessing is the heater core. It's been secret because I haven't been able to locate it for months. Overflow reservoir keeps going down almost to empty but through pressure testing a couple of times and checking what I could in plain sight-upper and lower hoses, radiator and around UIM- I couldn't find anything. Then I started to notice carpet on passenger side floor was retaining moisture, getting a little soaked. The fluid was definitely coolant. But how? Thought I left a bottle in there and it spilled or something. Couple nights ago however, finally went to investigate further. Took off black plastic trim below radio, vents and glove box and saw a dripping of coolant on a wire. Looking closer, noticed a black box-like compartment that had small couple of beads of coolant gathering at the seam, or where the two halves of this black box came together as one. Box was about a foot long and six inches deep headed towards the firewall. Is that where the heater core is? Couldn't find any more to unscrew so this is where the mystery sits. I thought coolant just cycled through tubes, through the engine, the throttle even, through the radiator then the overflow container and back through the engine again. Any ideas as to what that area is and how to disassemble it? '98 Lesabre 3800 Series II. Thanks for any replies. Also, there is external drip which tipped me off originally. It's right below that same area of the car, but falling off the undercarriage. I want to say it's just forward of the ball joint but otherwise continuing vertically down from the firewall and going on to the ground.

 

[misterRollsRoycer]

I checked out a short video on you tube about this. Guy on video was replacing heater core. That basically looks like what is going on. He also stated, not many videos about this on internet but that Auto Zone had a good layout on repair guides for it. Went there and was compelling enough info about diagnosis that this was indeed my problem. Water and coolant mixture together on passenger side floor. Heater core is in little black box-like compartment above floor and behind glove box. Will have to remove A/C actuator valve (due to manual climate controls on dash) and then can get at heater core for inspection and most likely replacement. This of course after detach neg. batt. cable, disable airbag system, and drain coolant. If anyone has done this, would you suggest any kind of a reverse flush to the heater core? Or can you just pull out the unit by itself and spray out inside with a hose? That is, if it is just a flush that needs to be done. Also, at times when I needed to top off the overflow reservoir with coolant because of this leak, I might have noticed some gulping sounds. Air bubbles flowing into system? Could that be a primary cause of this leak down into passenger floor boards, and also around the heater core? Thanks for replies.

 

[DonP]

A back flush can help a clogged heater core (typical symptom - no/poor heat), but I would not expect it to help a core leak.
But using a stop-leak product to fix a coolant leak could lead to a clogged heater core under some circumstances
I would not expect air in the system to be the source of a leak either.

 

[Spriteman]

Would suggest draining your coolant as well as possible - then I would flush with clean water - that way when you do disassemble the evaporator/heater core you won't worry about spilling coolant all over your interior/carpet. Turn your heater lever to high so the maximum coolant/water will flow through the heater core while flushing. BTW - when I say flush I'm not talking about a high pressure shop flush - just take off the inlet hose to the heater core or the radiator hose and put your home water hose in that and turn on high - that will be enough cool water to keep the engine cool while you're getting all of the coolant out. And it will serve to remove any debris that might be in the system.

There's quite a bit of disassembly to do when doing this job so be ready for a good amount of time. If you can find some directions for your year vehicle that will help - maybe a good youtube video on the topic.