My 91 has an intermittent low coolant message and the coolant level is OK. Where should I look?

 

An air bubble maybe?

 

How do you know?
Has coolant system been " burped" to clear air pockets?

Coolant level sensor in the radiator ; pass side below radiator cap

 

This is a common problem, I've had the same thing happen on both my '87 and '86. On both cars, it was an air bubble in the coolant that needed to be "burped". If you're not losing any coolant (on the ground or burning it), the system probably just needs to be burped.

I have never been able to find a bleed port in the system, so I do it as follows. Start the car when it's cool and open the radiator cap. You'll see it full of coolant. Rev the engine to about 2k RPM and wait for the thermostat to open. When it does, the coolant level will drop significantly in the radiator and the low coolant light will come on (if it is working). Top off the radiator with 50-50 green coolant/water mix. Replace the cap and go drive it. Afterwards, let the car cool down completely and repeat several more times. After each drive, check the coolant overflow tank and ensure it is at the proper level.

My driveway is sloped, so when I burp it, I park the car on the slope with the radiator on the high side. Not sure how much this helps push out the air, but it makes me feel smart.

I've heard of people trying to bleed it through the coolant hose on the throttle body (highest point in system), but I have never tried that.

 

Just to clarify.
Add the coolant while holding the revs up and replace the cap before letting the revs drop so as to "pack" the coolant in
If you let the revs drop before the cap is on ,the coolant you just added will blow back out in your face

 

That was the highlight of my day the first time I attempted the packing procedure....

 

Proper protective gear would help to

There are a few parts in the block that seem to always cause air pockets. The freeze plug is sometimes the culprit and some sensor that I cannot remember on the bottom drivers side?

Running while pouring helps. The first thing I do is squeeze the coolant tubes with the motor off. I've pulled more than a few bubbles out that way.

 

Or....the sensor could be bad.

 

Here is a good How To write-up. Also, make sure that you drill the relief holes in your thermostat and you will never have to deal with this problem again.

FWIW

 

That did the trick. Thanks for the help.

 

You're welcome

 

And thank YOU for posting the follow-up so we know what it was. Sometimes someone will ask a question, get a bunch of suggestions, and that's the last we hear of it. Always good to know the actual diagnosis.

 

 

Just thinking out loud and a question to everyone. Am I correct to say the burping procedure only applies to 1989 or earlier C4's that does not have a surge tank arrangement. The surge tank arrangement was designed to eliminate air pockets in the previous system.

From what I know, the surge tank on 1990/1991 cars are mounted at the highest level of the radiator system so any air will be automatically purged out once the thermostat is fully opened.

I can understand an air pocket developing before the thermostat opens, but once the thermo opens the air will be pushed to the surge tank and out to through the vent to the over flow tank.

Is my analogy correct?

 

Your making way to much sense there.

 

I just replaced my opti and water pump. Refilled with 2 jugs of 50/50 antifreeze. Low coolant light came on, bought another jug used 1/2 of it 5 days ago.

I drove 3 hours today and got the low coolant light again. I added the remaining 1/2 jug, the light intermittently comes on.

The car is not overheating, I dont see a leak anywhere.

Checked the oil, its normal! The tranny oil is also normal.

Its my daily drive (my only vehicle), what is it? I did not burp the system; however, I think 3 jugs is a bit much.

Please help!

 

LT1 's have bleed screws that you use to get the air out of the system

http://forums.corvetteforum.com/c4-t...procedure.html
http://forums.corvetteforum.com/c4-t...on-an-lt1.html
http://forums.corvetteforum.com/c4-t...ng-system.html
http://forums.corvetteforum.com/c4-t...em-93-lt1.html

 

Still losing coolant! I am at a loss. I have about a 1/4 of the 4th jug left now. Still no froth like oil or tranny fluid.

 

Do the 90 and 91 L98 cars have a Low Coolant sensor for sure ? I have a 91 and do not see a sensor on the right or left side of the radiator and I have looked for one many times.

 

I have a 1991 and wonder about this (surge tank question) also.

XR_Strider_GuY,

I can not find a low coolant sensor on my 91 radiator. Do you see one on your 90 and if so , where is it?