P0128??? Thermostat? water gauge is dead, both cooling fans run non stop

[Linuxglobal]

Hi everyone, I need some help with my dad's 2001 Olds silhouette. Just recently his water temp gauge dropped and hasnt moved. It only moves when you turn the key, maybe about 1/8 inch and then drops again, so im guessing the gauge works.

It came up with an error on the obd2 reader. P0128 (coolant temperater below thermostat regulation). So we dont know whats going on with it, the heat and a/c work and the engine revs are normal. But the front cooling fans run non stop, both of them.

I went to the dealer and they said it may be the thermostat. Ive searched this forum on the montanas as well and some ppl have had success in chaning the thermostat and other have found other problems such as the intake manifold gasket>???

I bought the thermostat and I plan on installing it today. Im stuck out of ideas on how to get to it.

1. REmove the air tube
2. REmove throttle body
3. Remove some of the coolant
4. --- stuck... how do i get to the bottom screw of the thermostat pipe?
Theres some exhaust bypass with a shield. ANybody know the type of key/tool that i need to just loosen the bottom screw.

I also want to find out from other past experince how to truly tell a thermostat failure from anything else. (person with the intake prob had a p0128 come up)

Any advice on the procedure would be greatly appreciated.

Thank you,
Ciprian

[GregA]

Originally Posted by Linuxglobal

...the heat and a/c work and the engine revs are normal. But the front cooling fans run non stop, both of them.

Ciprian,

I was wondering if you had considered the Engine Coolant Temperature (ECT) sensor and any wiring to it?

Since your heat is "normal" and the system thinks your temperature is "low", I would suspect that sensor.

Here is a link to to how and why the fans turn on:

Engine Cooling Fans

And here is a link to some more information about the ECT, like where it is and how to test it:

Engine Coolant Temperature Sensor

Let us know what happens.

Take Care,

[Linuxglobal]

Thank you Greg,

About the sensor, i went to my dealer to buy the sensor (right beside the thermostat) and they told me if the gauge doenst work and P0128 comes up its the thermostat, not the sensor. I originally wanted to replace the sensor. I measured the sensor and it reads 5V when the engine is warm.

So i think its something else that has caused the gauge to stop working. Everyone seems to be hinting at the thermostat. I think the coolant has also been mixed (green + orange) is that bad? Ive been told its ok, but the corrosion factor is increased or something like that. Not too sure.

My dad bought one of those bent wrenches and we're gonna take the TB module off and see how it turns out. I hope its the thermostat, its surely a lot of work just to get it out.

I just hope it fixes it, then ill see if the fans still run, is there any way that you can tell if the current thermostat is broken in the car, in or out of the motor? Just so i know at least when i have it all apart.


Thanks,
Ciprian

[Linuxglobal]

BTW: The car interior heat and ac work as they always did. its just the gauge that doesnt do anything so i no longer know if the engine temp is ok. It doesnt show any signs of overheating and its cool to touch, but the fans worry me. Other than that no other physical factors are visible.

Thansk again,
Ciprian

[GregA]

Originally Posted by Linuxglobal

Thank you Greg,

About the sensor, i went to my dealer to buy the sensor (right beside the thermostat) and they told me if the gauge doenst work and P0128 comes up its the thermostat, not the sensor. I originally wanted to replace the sensor. I measured the sensor and it reads 5V when the engine is warm.

So i think its something else that has caused the gauge to stop working. Everyone seems to be hinting at the thermostat. I think the coolant has also been mixed (green + orange) is that bad? Ive been told its ok, but the corrosion factor is increased or something like that. Not too sure.

My dad bought one of those bent wrenches and we're gonna take the TB module off and see how it turns out. I hope its the thermostat, its surely a lot of work just to get it out.

I just hope it fixes it, then ill see if the fans still run, is there any way that you can tell if the current thermostat is broken in the car, in or out of the motor? Just so i know at least when i have it all apart.


Thanks,
Ciprian

Ciprian,

You have 5V at the sensor? What about at the other wire?

The 5 Volts is coming from the PCM. The other wire should be something less than 5 volts. The sensor is just a "Thermistor" that changes resistance according to the temperature.

If you have 5 Volts on BOTH sides (wires), I would make a "logical guess" and say that the wire that carries the signal back to the PCM is OPEN. That would be why the gauge doesn't move and the PCM thinks the engine is cold.

As for the FANS running all the time:
The cooling fans are controlled by the computer (PCM). It will keep the fans ON all the time if it thinks there is a problem (your Error Code), and will keep them that way until the code is cleared.

I believe the thermostat is working, because you say your heater is fine and there is no overheating of the engine. If it was stuck closed, the engine would probably overheat. If it was stuck OPEN, AND the fans are always running, I don't think you would have much heat from the heater.

BTW, you can test the thermostat by putting it in a pan of water and bringing it to a boil. Watch to see that it OPENS around 195 degrees F. Take the pan off the stove and start mixing in cold water. It should CLOSE again.

Let us know how it goes.

Take Care,

[Linuxglobal]

Took out thermostat, replaced and reassembled the entire unit. Fans are OFF and the gauge works.

The only problem i ran into is the coolant. How do you purge the system? I dont think the water is flowing through it since i opened the radiator cap and nothing came out even after the car ran for some time. It also doesnt overheat but i think it will since the coolant is not being circulated.

Some tips on the procedure would be very helpful.

Thanks in advance,
CIprian

[Linuxglobal]

GOT it guys. All fixed. Temp stays below the normal line and the car runs fine. No more fans !!! I found out how to leak the coolant with the bleeders.

Thanks everyone, the thermostat was the culprit.

Ciprian

[tanker33]

I have just ran into the same problem with a friends Venture. I just replaced the thermostat. And attempted to bleed the system. Everything seems to be fine. Except...... The temp gauge is still not moving and the SES light is still on. I think we are going to go ahead and replace the cooling sensor. But I was more interested in seeing if you remembered the sequence of bleeding the system. I may have held my head at the right angle or lifted the wrong foot.
Thanks ahead of time for any assistance.

[Linuxglobal]

to purge the system you just have to remove the radiator cap and keep on topping up the coolant level through the rad.

Then open u the bleed screw on the waterpump side (not the thermostat) and wait for the level to rise. Give it a few minutes and the coolant will start to pour through the little bleeder.

Then you can close the bleeder and start the car. See if the rad level drops and top it off if it does. Occasionally open the small bleeder to check if its still a solid stream. Close it before turning off the engine or it will take in air.

Open the thermostat bleeder while the engine is running and check for the solid stream and then close it up again.

After a few minutes the engine should warm up and the thermostat will open up, you will be able to tell since the rubber hoses will weaken up.

The temp gauge should work after the sensor and thermostat replacement.
I just played around with it and left out all of the air at the waterpump bleeder. I did have to replace the waterpump a while back since the car lost a lot of coolant in a deer accident. The new pump isnt as good IMO... but the same procedure worked... make sure the engine is not overheating when you do this, get someone to watch the gauge, if its working.