Ok. I picked up a Stant Superstat part # 65849 and the thermostat seal part # 27277 that the Stant book calls for. I defiitly don't remember seeing this seal in there when I changed the thermostat before.

Do you know if this seal is supposed to go on top of the thermostat? It definitly will not fit on the bottom side of the thermostat. I hav't pulled the old one out yet so I cant tell how it'* supposed to go together. Also the Stant catalog did not have a listing on the oring for the outer diameter of the goose neck which would be GM part # 12337901.

I also called my GM dealer and he said there was a note in the parts catalog to remove the seal. Seems opposite of what the Stant catalog is saying. Go figure.

Guess I won't know until I get into it.

The primary cause for poor heat (as long as there'* SOME heat) is not the airmix acutator (this is regarding 87-99 Bonnevilles).

The most common problem is a clogged heater core. The procedure in techinfo will restore most systems to their greatest potential. My 93 increased airflow by 30% or so by doing this.

A little carb cleaner and a garden hose will restore airflow through the heater core in a way you can't imagine.

Is it possible that your cleaning method can go a ways for flushing the coolant? It seems that the coolant would be clean until I turned the heat on. Even if I flushed it with the heat on, it didn't seem to flush it clean. I know a bit of crap in my cooling system is the least of my worries at this point, but i'm just curious

And that seal goes ontop of the tstat, and should make the tstat sit in the housing. If you can make it fit with it in the housing [nice tight seal], then do so. If not, place the tstat in the hole [without the seal], then place the housing in with the seal properly mounted in the housing. Either way, the seal MUST be in the housing.. otherwise it may end out somewhere you don't want it [like your radiator].

feel the inlet and outlet heater hoses to the heater core.
One should be hot the other luke warm.

Hi I have same problem only cool air coming out of defrost or floor,its driving me nuts,spent days on this.
therm changed
new aircondition,rad last summer
top rad hose hot
cleaned evaporator and took out heater core and flushed it,heatig up nice
checked all vaccuum hoses fixed one near intake manifold
checked hvac programmer vaccuum hoses seems ok
blower blows well
acuator is moving left to right just fine.
I disconnected actuator arm and manually blocked ac with air mix door ac coolness was prominent over heat
Display is not blinking,everything seems fine but no hot heat,if I put blower on lower speed it will be warm but not enough to heat car,put blower speed high and turns to cool.
so there is heat there just a/c is over powering it
I went into so much detail because it is driving me crazy,what can it be,could it be the actual dash control module or something
I would appreciate any help and thank you so much before hand ,this sight has taught me alot
1990 BONN SSE DIGITAL CLIMATE CONTROL 3800

Seems lik my problem is cured thanks to Opensourceguy.

I removed the goose neck (water Outlet) in order to inspect the thermostat for the seal. There was no seal in there at all. I procured a seal at my local chevy dealer and a my local VIP store. Now I have two seals. One for a spare. I replaced the thermostat with a new one while I was in there just for the sake of it. I put in a Stant Superstat
( part# 65849). I don't believe there was anything wrong with the thermostat. I'll keep it as a spare.

The only thing I didn't like about the seal was trying to decide which way it went on. I tried it both ways and one way fit a little tighter but did not allow the water outlet to tighten down evenly. So I flipped the seal over, it fit a little bit looser, and I was able to get the water outlet to draw down in fairly evenly as I tightened the bolt. I just think that a water outlet with only one bolt on one side is not that geat of a design but then again it'* real easy to remove and install and it has never leaked. Go figure.

I now have much better heat and the gage on the dash reads up to the first line in about ten minutes at an outside temperature of 45 degrees.. Gage now will climb just beyond the first line and stay there. Sweet. Now the upper radiator hose gets hot to touch. It'* too hot to hold my hand on it for more than 5 seconds.

For those that are so inclined, here are the part #'* on the seals

Thermostat seal, Gm part# in group# 1.252 = 12337901, cost about .59 cents.

Same thermostat seal, in the Stant brand = 27277, cost me .99 cents.

Water outlet O Ring, GM part# in group 1.154 = 12337860.

Sweet, looks as though you are good to go. I apologize that I did not specify which way to install the seal, but it has escaped my memory. Either way, as long as you are happy with your heat, then that'* great.

Oh yeah, and the one bolt housing, is pretty retarded. But it does work, and as long as you keep it even [IE installing it completely before bolting down, and not over torquing], it won't leak.

jdq: if your sure your heater core hoses are hot and you are getting good airflow,
The actuator door must be stopping short allowing cold air to mix in.
check for obstruction in the door, or an out of adjustment linkage.
The right side of the linkage arm just snaps up out of its holder, then you could push the door lever all the way to the left while the HVAC is on 90 and re-snap in.

Thanx for the reply
IM going to double check again but I had it apart and was swinging door by hand (acuator)while heat was on and I could feel a dominant cold A/C.Even now I pulled relay and I have some heat but when blower ison high it cools,it seems like maybe my core isnt that great and blower coolness on high is stronger ,grasping at straws here.
thanyou JDQ

are the hoses to the heater core hot?
Maybe the core is not flowing or has an external obstruction.