1 - Does this sensor monitor coolant level in the reservoir or in the radiator?

2 - If the level is low in the radiator is the system supposed to pull from the reservoir or is the reservoir only there to hold overflow from the radiator?

I guess what I'm asking is this...does the coolant system run both ways using the reservoir?

Timeline:
Vehicle purchased May 2013
Radiator Fan assembly replaced; coolant flushed; t-stat replaced; upper and lower hoses replaced July 2013
Radiator replaced November 2013

Fan assembly replaced due to codes and failure of passenger side fan; decided on tstat and coolant flush and hoses to be on safe side

Radiator replaced due to hit and run on my monte. Radiator popped a seam (or something) enough to cause a serious leak. INS company wouldn't pony up for radiator (but that's another story). Replaced radiator out of pocket.

Issues:
-Temp gauge shooting up to redline (hit redline this AM for first time)
-Monitoring temp with Scanner and guage is accurate
-Low Coolant Level message intermittently
-Temp will spike intermittently
-Heat from vents most of the time but not always...intermittently blows cool air
-No leaks noticed...nothing on driveway or in parking spots
-Reservoir is full (overfull)


Neighbor has pressure tester...will test soon. Been 20~ degrees lately in Wash DC area.

2002 Monte SS
144000~ Miles

 

My first question is...
Is it loseing coolant? Have you ever changed out the coolant elbows?
at 144,000 miles its way past due to have them replaced. If its not loseing coolant via drip that you can see on the ground..it may also be time for upper and lower intake gaskets to be changed... Pull of the oil cap and see if it looks like a brown milkshake residue on it.... Is/does the resovoir show signs of a brown milky substance? .... Why did you have to replace the radiator? If the sensor is mounted on the radiator..its there to measure the amount of coolant in the cooling system. Are you having cooling issues? Is it running hot?

 

The sensor sits in the radiator right below the fill neck, so that's where it reads.

Sometimes they just get dirty and gunked up and can throw the light, doesn't mean you are actually low.

 

Edited original message with more information.

 

The radiator overflow does work both ways

You truthfully might be experiencing air in your system OR a blockage. When Dexcool isn't changed frequently it can build up into a crud.

Was the system completely flushed really well when the radiator was changed?

 

With the obvious over heating issue (redline) It could be a cpl of things.
1) Theres air in the system thus causeing overheating and a lack of heat...due to airpockets..
2) Since there is no obvious signs of leaks... have you ever noticed what would only be described as a "sweet" smell either in the car or from the exhaust?...
3) But since you had to replace the radiator im leaning towards an air pocket. and the intermitten low coolant light is possibly when theres a pressure change and due to the residual air in the system...
Have you tried bleeding the system?

 

I cannot ascertain 100% if the system was flushed when the radiator was swapped. I was not on site.

I can state with certainty that the flush was done well when I swapped the fan assembly in July. Water coming from the radiator was clear.

I have not noticed large clouds of white smoke either nor have I noticed a "sweet smell".

I am really hoping it is not a failing head.

One other item...the reservoir stays full...even overfull. The level of the reservoir does not change.

I have not tried bleeding the system yet. Nor did I do that when the tstat and fan assembly were swapped. And I am not certain if it was done when the radiator was swapped either.

What is the best method of "bleeding" the system? Can I do it today before I leave work...cannot risk sitting in traffic on my way home and do not want to wait until 8PM tonight before heading home to avoid traffic.

Failing water pump I can handle...failed head gasket I cannot. At least not until January.

 

There should be a nut/bolt on top of the thermostat housing.
That's the bleeder for the cooling system.... "donot" start the car during the bleeding process. you need to get it under pressure(warm it up to running temp).... then shut it off..
Carefully open the valve slowly and let the air seep out...it may take a few times to get it all... Its not a 1 time process.... Once the air escapes from the system a solid stream of water/coolant should be the end result of the bleeding process....things should return to normal if done correctly. You may have to repeat this process a number of times.... I would also recommend "after" you get the air out of the system.... to do a pressure test to be sure the cooling system is still a sealed system.

 

Well this is going to be fun.

I cannot get the bleeder valve to move and I'm reluctant to force it.

Plus cannot get the radiator cap off to check on level in radiator.

 

If you can get the bleeder open, jack up the front end of the car while bleeding, it seems to help the 3800s