Bad thermostat or???

[xring]

My wifes 01 Grand Am GT lost heat and the SES light was on, I checked the code it was P0128. So I figured that the thermostat was stuck open. I replaced it, filled the coolant, ran it to temp with the cap off. It seemed fine so I took it for a drive. While driving it It lost heat and started to over heat.

I'm thinking that I have a bad thermostat.

Do you think I on the right track or is there something else I should be looking at.

Thanks,

Scott

[jonnythan]

What do you mean by "lost haet"?

Did you thoroughly bleed the system after you filled it back up?

[xring]

When the car is at temp, the inside heat does not blow hot, it did right when I replaced the thermostat, but then it stop working. I may have air in the system.

What is the best way to bleed the system, I have always just ran my cars up to temp with the cap off, should I do something else?

Thanks

[jonnythan]

Apparently the "run with the cap off" trick works great for the 2.4L but not the V6 engines.

I'm going to steal a page out of rixGAphx's playbook and do some copy/paste. Here's what he has to say on the subject:

"You MUST bleed the air out of your V6's cooland system.
The inside of the engine (the intake manifold in particular) is above the fill location, so air remains trapped there.
On the back of the waterpump, there's a vertical metal tube with a couple other tubes welded to it.
The top of the vertical tube ahs two brass hexhead screws, one inside the other .
Hold the larger (outer) hex still with one wrench, and twist the smaller (inner) counterclockwise the way you bleed brakes.
Fill the reservoir.
Coolant will seep out the bleeder as soon as the reservoir level reaches the proper level.
Close the bleeder.
close the reservoir (only tighten the pressure cap as tight as an average woman can easily do one-handed. Any tighter nad you will damage or distort the delicate rubber sealing washer the contains the 14 or 15 psi pressure).

Drive the vehicle to operating temperature, so the coolant flows out of the radiator.
Return home, and allow system to cool.
REPEAT the bleed to procedure, to remove air that *might* have been trapped in the radiator when you did the original bleed."

[97BLKGAGT]

This actually happened to my buddys jeep. you might have an air pocket that the coolant cant get around try pressure testing the system and see if it holds

[rixGAphx]

Y'all are on the right track, and jonnythan is spot-on.

This V6 under the low GA hood MUST have the coolant system bled, and GM is so paranoid about this issue that they installed the special bleeder assembly.
GM has never spent a DIME for something that they didn't have to, so you better believe it's a necessary feature.

Doesn't matter if you've driven Jeeps or Jags, VW's or Volvos.
Doesn't matter if you've beld Ferrarri's by leaving the cap off.

THE 60*V6 IN THE GA MUST BE BLED THIS WAY.
Be careful with those fragile brass screws, they like to 'SNAP'!

Yes you have an air pocket, and no, it won't go away by itself.
It will hold pressure during a test just fine, the air pocket has nothing to do with that.
* * *
P0128 = Coolant Thermostat Malfunction
Since the heater wasn't blowing hot air, you were right to suspect and change the t-stat.
But, there are other problems that would cause the same symptoms, and the PCM (Powertrain Control Module, the engine-tranny 'puter) that reported the code is pretty stoopid. It never really KNOWS if the t-stat is malfunctioning, it just knows when there's a problem that SEEMS like it's t'stat-related.
That's what it was reporting.

The original problem may still be there, unaffected by the replaced t-stat OR the 'air pocket'.

Certainly, the 'symptom' of 'no heat in cabin' remains.

Let's back up a bit.
Prior to the t'stat replacement:
1. What temperature was being indicated on the gage, when the engine was warmed and running?
2. When you first opened the reservoir cap, how low was the coolant level?
3. This is a 7-yr old car, so about 85k miles; is this the original coolant?
After the t'stat replacement, you took it for a test and said "While driving, it lost heat and started to over heat." What do you mean by 'started to overheat':
* The needle started climbing on the gage; say, past 220*F?
* About how high did the needle go?
* Was there actual 'boilover', of liquid bubbling out the pressure cap?

I'm really concerned about this, since the V6 is so [EXPENSIVELY] prone to cooling system problems, and your experience (LOSING cabin heat, + P0128 code) is so unusual (I have never read on this site of ANYBODY getting that code, despite about a 100 GA V6's having cooling system issues in the past 4 years).
Specifically, you could be in the early stages of a LIM gasket failure, and all this is merely masking your true symptom (the Mysteriously Disappearing GM Coolant).

Standing by,
-Rick

[xring]

Here is some more info.

1. What temperature was being indicated on the gage, when the engine was warmed and running? The gage was on the very low end, I don't know the exact temp.
2. When you first opened the reservoir cap, how low was the coolant level? The coolant was at the correct level and not low.
3. This is a 7-yr old car, so about 85k miles; is this the original coolant?
The car actually has 160K on it and it is not the original coolant.
After the t'stat replacement, you took it for a test and said "While driving, it lost heat and started to over heat." What do you mean by 'started to overheat':
* The needle started climbing on the gage; say, past 220*F? The needle sat at 200* for a while then it went to 240*
* About how high did the needle go? I shut off the car before it got to 250*
* Was there actual 'boilover', of liquid bubbling out the pressure cap? It was not a "boilover" and there was no liquid bubbling out of the cap.

I should also clarify that the SES light came on last Wednesday and she lost heat this Monday. I don't know if the two are connected.

The car has never used any coolant that I know of. If the LIM gaskets need to be replace what issues would I be seeing?

I'm going to bleed the system tonight and I will post what I find.

Thanks for your help.

[rixGAphx]

I should also clarify that the SES light came on last Wednesday and she lost heat this Monday.
I don't know if the two are connected.

The car has never used any coolant that I know of.
If the LIM gaskets need to be replace what issues would I be seeing?

I'm going to bleed the system tonight and I will post what I find.The primary sign of LIM gasket failure is the mysterious loss of coolant (it leaks out the ends of the heads and evaporates, so you never see/smell anything, oher than needing to top-off the reservoir frequently.

Next sign would be a LIM gasket leaking internally, whence the coolant flows into the crankcase and the oil is homgenized into a chocolatey milkshake appearance.

Third sign would be inexlicable overheating, on top of mysterious coolant loss.

Since you don't have coolant loss, you have allayed my LIM gasket fears.
Since there wer no other untword events (boil-over, in particular) I think you'll be fine by bleeding it.

There's a *slight* chance that the new t'stat was pemanently damaged by being 'baked' in 240*F air (as opposed to being boiled in 240*F liquid); the result would be that it also sticks.
You won't know until you bleed and run the engine.
My feeling is all will be well.

Carry on. :D :D
-Rick

[xring]

Well, I bled the system and ran the car to temp. I had heat inside the car for a few minutes than it stopped. The temp also rose up to about 230*+. I shut off the car and let it cool for a while, when I started it up after the cool down, the Low Coolant light came on.

I think that tomorrow I will bleed it again. I think that I will get the thermostat figured out but I'm starting to wonder if my heat core is plugged.

Thanks for your help.

[xring]

Ok I replace the thermostat with a good one and it seems that the cooling system is plugged. I bleed the system, run it to temp and the cooland starts coming out the over fill. I'm thinking that I'm going to bring the car in and have the system flushed, do you think I'm on the right track or is there something else I should try first?

[rixGAphx]

On the right track as far as the entire SYSTEM having a plug; I doubt it's in the ehater core, however..
Your heater core may well be plugged, preventing heating of the cabin.
But that would have NO effect on the ability of the system to cool the engine.
You can litterally cut both heater hoses and plug them both, and the cooling system will run fine. In fact, if you're halfway passed nowhere and a heater hose or core leaks, that's exactly what you do.

You now have expressed 'coolant loss'.
My fears of LIM gasket leakage are getting very strong.

Have you replaced the pressure cap, and is it holding 14 psi (if the top of the palstic reservoir neck is damaged, then the cap's gasket won't seal)?
When you 'fill' the reservoir, you're leaving 1" or so airspace from the liquid to the bottom of the filler neck, for the cool liquid to expand into as it heats, right?

When you 'bleed' the system, you must do it TWICE:
Once to remove the air from the top of the engine; then warm the engine and drive, and allow it to cool.
Then REPEAT, since the air previously trapped in the radiator has now moved to the top of the engine.

BUT, it sounds to me like you have a complete FUBAR, and you really need to use some UV dye and find the leak point.
A complete chemical flush of the system would be in order IMO.

Good luck,
-Rick