Hey guys, did a quick search here before posting, couldn't find anything relevant to my model (at least nothing I haven't already tried). Here goes:

I live in lake Tahoe, and as you know this time of year it gets pretty damn chilly. A couple weeks ago I discovered that my heater wasn't working very well, but I attributed it to a low coolant level since my radiator was leaking. I would top it off and the heater would blow *warm* air for a while, but it was intermittent and seemed to only work when I revved the engine slightly.

I then figured it wasn't simply a low coolant level, so I tried flushing the heater core with a garden hose. No problem there either. After talking with my dad some, we each figured it might be the thermostat.

I checked the thermostat, and lo and behold, there *wasn't* one. I got a replacement and put it in, and it helped tremendously. The engine would warm up much quicker and the heater function was more consistent.

Next I got a new radiator, since stop-leaks are a no no. I filled it up with new fluid, checked for leaks, found none, and figured I was good. But I wasn't.

As I said, the heater works way better than it did before the thermo and rad replacement, but it still doesn't blow HOT air, and the passenger side vents still seem to blow COOL air.

I bled the cooling system by running the engine with no rad cap, partly because the cap is the highest point but mostly because the bleeder screw was stripped out (and it's one of the ones that's recessed, so vice grips aren't gonna work either).

I'm wondering what I should check next. How critical is it to open the bleeder screw to purge air? Does the "running with no cap" method work just fine? At this point I'm thinking it's either air still in the system, the heater control valve, a malfunctioning vent door, or maybe the water pump. Or the car's just so damn old the heater's as good as it's gonna get...

Any advice you guys can offer is appreciated. Thanks, and sorry for the lengthy read

 

Usually, the cooling system will bleed itself of air by going through several warm-up and cool-down cycles. Leaving the cap off is unnecessary and counterproductive.
If you got a good flow of water through the heater core with the garden hose, then we can rule out a plugged core as the source of the problem. Incidentally, exercise extreme care when attaching a garden hose to your cooling system as city water pressure can be as much as 90 psi whereas the cooling system was designed to operate at about 16 psi, so there's a potential for doing some serious damage.
Anyway. there's a door within the heater plenum called the "blend door" that opens and closes to mix more or less outside air with heated air to control the temperature. If that door isn't operating properly, performance can suffer. See if you can get a shop manual like a Haynes that descrribes the operation and repair of the heater. Parts may be hard to come by for that old a vehicle.

 

Thanks for the input Cotter! I'll consult my Haynes manual and see if I can check the blend door, seeing's how it seems relatively simple and likely the problem at this point. I guess worse come to worse I can live with what I got now, since the vents blow warm enough to defrost the windshield Thanks again! I'll keep you posted.