heater core??

Ok I see it's a pain lots of info on that so before I jump in I just wanna make sure. My 94 olds bravada seems to be shooting coolent gas out of the defrost mostly in the rain, higher elevation, cold weather, and/or longer trips. Seems to blow warm air when on. I just had the cooling system blown out good. Seems to be useing coolant so I put straight coolent in. Any info or opinions would be great before I tare into it thanks.

The switching vents is a (lack of) vacuum issue. Trace your vacuum lines and replace any that are nasty or brittle or cracking.

Is there a puddle on the passenger side floor? Can you smell coolant inside the truck? If not, it might not be the heater core.

If you're losing coolant, you need to find the leak. Could be the weep hole on the water pump, could be the intake gaskets, could be the head gaskets or the head...

I can smell it I haven't noticed a puddle I did notice one outside under the pass. seat and thought it was the coolent bottle over filling I've looked for a leak and not found one but it's hard sometimes. The vacume lines? under the dash or under the hood? Thanks

Moisture on the windshield just above the defrost outlets when the heat is on generally indicates a leaky heater core.

Moisture there with the air conditioning on generally indicates a cold windshield and condensation of humidity.

Just above the passenger floorboard, under the dash, is some plastic ductwork. Wipe the bottom of it with your hand then see if your hand is wet.

Ok cool thanks I don't use the ac since it's never worked. I'll go check it out in a bit

I found a wet spot on the floor and the rad. is down to the heater hose so I geuss it's the heater core I might cap it off/bypass it till I get a new one would that be ok?

I found a wet spot on the floor and the rad. is down to the heater hose so I geuss it's the heater core I might cap it off/bypass it till I get a new one would that be ok?

Good move.
Coolant is poisonous, even in a vapor form, so if you cannot fix it right away, at least bypass the core for now, so you do not breathe the stuff in.

The easiest way is to remove both heater hoses and hook them together using a 5/8 inch hose coupler and hose clamps from a hardware store.

Good point I had a car that got really bad and I'd start feeling sick on longer drives. Another reson for safty sake is vision even if I put towles over the defrost vents it fogs up and that stuff dosen't just wipe off it smears and fogs up twice as fast. Nasty stuff.

Ok thanks guys for al the help got it in and done worked great (Except I didn't hook the mirror swtich back up) for about a week or so and now the fan dosen't work puts out hot air but no fan. Is there a relay that fries out alot or go straight for the fan?

Good work, thanks for the update beatdr,

It might be the fan motor. With the fan switch turned on/keyswitch on/engine off, tap on the fan motor under the hood and see if it starts or growls.

Well I got a new one in only $26, easy to do. The new one was diferant has a gasket flange thing made it hard to get the screws through and had to dig up a screw to ground it, be nice to have longer ones make it alot easier couldn't get one in. Also the power plug was on top and the vent tube? was offset quite a bit barely able to use stock hose might have to figure something differant out. Anyway thanks agin for the help.