Leak from heater core-or not?

[Skigirl]

I have a leak into the cab pass side floorboard close to the tranny hump. It's leaking with the truck off and parked, when it rains. The heater works, no smells or leak when heater running. No leak at the tranny hump seal, no leak at the windshield. The insulation on the lower part of the firewall just under the box that houses the heater core is wet, but all is dry above the heater box thing.

Can the leak be coming from a messed up seal that's holding the box to the firewall or the other box (evaporator?) inside the engine compartment? (Sorry for the lack of correct terminology... I'm a newbie)

 

[JimmyJuneau]

Your widnows arent fogged up? (all the time)

1985 GMC JIMMY

 

[Skigirl]

No fogging. The only time anything leaks is when it rains.

I read Grimmy's write-up and the rain is getting into the cab from somewhere around that area. But because there's no collant leak, and only leaking in the rain, I'm stumped.

 

[taterblazer]

If its the heater core it should have anti freeze in it. That's if you have anti freeze in your coolant? If your radiator level stays topped off and you don't have to add any that's a good sign also.

 

[Blazer_Boy]

Your tongue can tell you what it is. Suuuuure, you're not supposed to taste the stuff but just enough to get your finger wet and a little taste will tell you if its coolant of not. I had a similar problem, it was my winsheild gasket. When I pulled my winsheild out, the bottom of the frame had lots of holes rotted into it. Some were over 1" long. I cracked open a tube of fusor body glue and glued pieces in from behind and held them with a magnet till the stuff cured. Then a pinch of bondo to smooth things over and now you can not tell. I could have welded, but I'd probably burn through and I had some tricky angles to get the gun or grinder in to.

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[Skigirl]

Nope, not coolant.

Blazerboy, when your windshield leaked, did you have leaking only down at the bottom end of the big box that houses the heater core? That's the only place where it's wet, and it's wet all along the very bottom of the insulation stuff that's mounted to the firewall, but only at the bottom. None of the insulation at the top is wet at all.

 

[Blazer_Boy]

Well on mine when I pulled the glove comparment and the vent tubing, I could see the bad spot at the bottom of windshield frame. It was a big patch of rust and flaking paint. My guess on yours is that you've a leak somewhere in your cowl area and its collecting in your heater box. I would take off that box and have a look around. That way you can have some idea before you go as far as pulling your winshield or cowl panel...... D'oh I should have check your profile for what year truck you have. The cowl panel is easier on the '73-'80 'cause it just has a plastic screen covering the thing. The '81-'91 are a little harder because you have to pull wiper blades and take off that metal piece.


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[kilroy]

Check the firewall inside the engine compartment, where the 2 lines to the heater core pass through. There should be putty around both pipes. If not the water could be spraying up from the road into these gaps. You can get this putty from NAPA for $12.00 it is made by 3M. 3M part number :051135-08578

 

[Skigirl]

Thanks guys. Kilroy, it's wet just sitting in the rain not moving. Blazerboy, I have a 76. Underneath that plastic piece (I assume that the cowl is the space underneath that) there's sealer stuff at the edges, and of course the metal is slanted so that rain would pour away from the cab. If the seal in there is leaky, would that let water seep inot the heater box that's in the engine compartment and then drip into the cab from there?