93 Cutlass Supreme - overheating, low coolant

I have a 93 Cutlass Supreme S with a 3.1 and it is driving me insane. I have replaced the thermostat (3 times actually) and the water pump and flushed the radiator but still I cannot figure what is causing it to overheat. The low coolant light is always on and the coolant level is not low. Some times the car will run fine but usually on any cross town trip it will either 'boil' when I shut it off or it will shut off at a red light on its own. When it shuts off, it will restart but as soon as I put it in drive (or reverse) it shuts off again. I am out of ideas, out of money and out of patience.
Somebody Help!

:banghead:

Welcome to AF netjunkie2 !

Did you bleed the cooling system of any air?

Air can get trapped in the system and your water pump cant really pump air, so it heats-boils over.

The low coolant sensor could hav an air bubble on the sensor, it'll giv the low level light.
Tap or hit the coolant resivour to see if it'll clear the bubbles.

It could also just be bad and need replaced.

Also with the overheating,
it very well could be something else causing this.

Hav you seen any milky looking stuff in the oil?
That would indicate you probly hav a LIM gasket leak.

Just make sure that you did not put the thermostat upside down or wrong direction.

Does your radiator fan working?

Start your vehicle and let it IDLE, around 7-15 minutes of Idling, the radiator fan should kick in and if not then your radiator fan needs to be checked.

Sometimes the coolant sensors might just need to be removed and cleaned as they have full of crud which prevents it from doing it's job.

Thanks for all the responses. I am going to condense the answers to all the questions in one short note here...

I have checked the fan, it does kick in...
No milky stuff in oil or radiator...
Thermostat right-side-up...
Bled air out of valve on top of thermostat housing (hoping that was the right way) mostly just spewed coolant mixture...
Not sure where to find the coolant level sensor. Tried to find it but not exactly sure what I'm looking for.
One other note... when I went to bring my car home the other night (after it's overnight stay on the side of the road) I cranked the heater up full blast (yeah, in Alabama in August) and made it home fine with no over-heating, boiling, bubbling etc. The radiator cap was not even too warm to touch. Significant? Helpful?

Sounds like thier still might hav been air trapped in the heater core.
Might try bleeding the air, but this time tuen on the heater :thumbsup:

To get to the coolant sensor, its located on the coolant resivour. You will most likly hav to remove it to get to the sensor.

Good Luck

Also, check for collapsed hoses around your cooling system. Start your vehicle and let it idle for 15 minutes or so. It should be enough for the radiator fan to kick in and then check the hoses to see if any one of them have collapsed.