My low coolant light flashed on after starting my car up yesterday. This morning, I checked it and the radiator was full and the resovoir level is where it should be. I started it up today and the low coolant light came on and stayed on? Again, the levels look fine.

Before I assume it is the sensor or wiring, is there something else that would cause this?

 

C5 - Curious as to your outcome; I get it once or twice a year with the same check = full as you.
Vaguely remember pressing the Reset button to clear the alarm.

 

To clear codes, I believe you dissconec the negative battery terminal for 15 minutes then reconect it. Mine did that before with the low coolant coming on during driving and it was a bad coolant sensor. Might be your issue.

 

Had similar problem at thanksgiving. temp climbed up near over heated climbing mountains for hours at 0-10 mph in traffic. Then a few days later lowcoolant light would come on till car warmed up. Plastic overflow tank was was OK but reservoir near fire wall was empty. Iwas surprised because everrything had recently been checked. So I filled the black tank near firewall and everythhing has been fine for about 3-4k miles. Knock wood. I still have an uneasy feeling about this. car has125k mls. Pls advise as to outcome.

 

Theres a coolant tank near the firewall? Are you sure? What is it beside any details? Mine might be empty.

 

On my 91 It is inthe pass side corner by the wind sheild when you open the hood. It black with a radiator cap. It should be full of coolant.

 

I dont think I have that on my model. Ill have to check into that though just to be on the safe side.

 

hmm... I dont think I have the black tank either (I have to double check)? I have the off white resovour tank by pass side front tire. Is the black tank a LT-1 thing?

 

'91 L-79. Lt1 I wish. Overflow in front of pass front wheel and blk tank by pass side hood latch. Blk tank has radiator pressure cap and 2 heater type hoses going into it.

 

Could be you need to "burp" the system. Sometimes you get an air bubble in the system.

Do a search on burping the system. Simple and fast.

 

I think i know what's wrong, mine did the same thing, check the sensor it's on the pass side of the rad toward the engine, it's about 2/3 of the way up, on mine the wire was loose and it would light up in the car, to be sure i you have the right wire unplug it and start the car the light will be on steady, just make sure you have the proper connection and your good to go.
J-P

 

The black tank is called a surge tank, it seems. Do a search, like elefkow suggests, using "burp" and "coolant". There are plenty of pictures, instructions, explainations and refernces. This forum is great. Let us know how it turns out.

 

It's called a surge tank and your 86 doesn't have one.

 

Can't really burp an 86. You can pack it, however.

 

The low coolant light sensor is just a blade of metal that's immersed in the water. Un-plug it, and the light goes on. The sensor can never go bad, it's just a blade of metal.
If the light keeps coming on, ground it and drive the car around the block and up to speed. If it still comes on, it's the light circuit, not the water in the radiator.
If it doesn't come on, wait till the car is dead cold, get a new jug of antifreeze, start the car with the hood open, open the radiator cap, increase the speed of the engine with your left hand to about 1500 RPM, with your right hand, add the coolant. when it's full, with your right hand again, put the cap back on, THEN let the car idle.
Put the coolant sensor wire back on, and sit in the driver's seat, and watch. The low coolant light should not be on.
Take a drive, the problem shouldn't return. If it does, and the water level in the white overflow bottle in front of the right front tire is getting fuller, you need a new 5/16 hose that goes from just under the radiator cap down to the white overflow tank.
Then burp it again, (from dead cold) and see if it goes away.
When you service the cooling system, the temp will be out of sight! That's because there's water in the head next to the sensor, and you need to revv it a little to get the water flowing up into those air pockets.

 

Either the wiring is bad, connection is bad, the sensor is dirty or faulty, or the cooling system needs to be burped to let the air out. Disconnecting the battery won't clear that warning light, since it doesn't come from the ECM.

 

the early L98 level sensors are junk. The design is poor... the sensor is too high, in relation to the natural level of the engine, so it throws false readings.

more than likey, the sensor needs replaced. They get more and more troublesome as they age.

 

The 84-96 has a coolant overflow reservoir tank (white/clear) in the passenger side headlight area by the radiator. On the 84-89 coolant is added driectly to the radiator where as the 90-96 the coolant is added to the surge tank.

 

Thank you for all of your replies. This is what I did. I "played" with the sensor wire (turned, pulled, and then pushed and made sure it was in and set as far as it will go. I then disconnected battery. After about ten min I reconnected the battery and started the car up. No more light.

I drove it for about an hour and still no light. So far, so good. Hopefully that is the end of it

 

I will bet major sums of money that the work on the harness connector fixed it. The coolant level (as mentioned above) is NOT an ECM generated code, as such, it cannot be effected by disconnecting the battery.

These connectors are prone to wear. I would think the tang inside has worked a little loose. I would go into it and pry it down a little so it makes better contact. Also, a little contact cleaner would not be a bad idea.