I have a 1987 AOD vette, I just replaced the rad and now the "low coolant" light keeps coming on off and on? And i checked the coolant it's at the right level... any suggestions?

Thanks!

Bryan

 

You got fooled because you did not check the coolant level properly. You truly have a low coolant level. In C4's, the engine is lower than the radiator top and air gets trapped in the top of the engine. When the engine heats up and the thermostat opens and coolant begins to flow, the air bubble moves out of the top of the engine and the coolant level drops turning on the ,"low coolant" light. You have to , "burp" your 87, here is how. Starting from cold (never open a rad cap with a hot engine because the coolant will suddenly boil and hot coolant will squirt out and scald you), loosen the rad cap to its first stop and let the engine idle until it gets to the thermostat opening temp. Remove the rad cap and pull on the throttle stop at the front of the MAF to race the engine slightly. When the engine speed increases you will see the coolant level drop in the rad filler and then you fill the rad to the top of the filler, replace the rad cap and then let the engine back down to normal idle. Sometimes you have to burp more than once.

 

Check the connection at the sensor just below the rad cap. Or just follow jfb's advise, it's usually right on target.

 

Ok, I am having the same problem with my '92. I have done everything jfb recommends and still have the Low Coolant light.

I don't see the wire for the sending unit to check...where exactly is that?

 

On my 93 I think? the sender is in the tank up at the passenger side, just under the windshield.

 

Make sure all the hoses are tight. I had a problem on my 89 where the coolant would be low after I had driven it. After I tightened all the hose clamps it went away. It couldn't develop the vacuum necessary to suck the coolant out of the overflow tank back into the radiator when it cooled down.

 

I had this problem myself. Now all but a memory...thank God!

 

Alright gang, hoses are tight, I have purged/burped 1/2 dozen times now (and now I get nothing but fluid), added a bit more coolant (1 cup maybe?) and I still have a light. Temp gauge is constant 180 running down the road, no leaks, no funniness except that low coolant light stays light. I'm also getting a flat spot on my forehead.

 

JFB is correct. this method does work!!!

 

the low coolant sensor in the radiator is a little blade of metal that's immersed in the coolant. The water in the radiator completes a ground to a circuit that's looking for a ground to cancel the light.
unclip the low coolant sensor, and ground the wire.
If the low coolant light does not go out, you have a wire that's either cut, or your low coolant circuit is bad.
try it and seee. then tell us what you get.
just taking the wire off the sensor is the same as no water in the radiator so you have to ground it.
If the light goes out, check your engine grounds.
If there's no grounding cable or twisted wire braids to ground the engine/trans combo, they are "above ground", and you need to address the negative path through your engine. If the ground path is not there, your car can do wierd things.
there is a ground path cable at the back of one of the heads. try adding a battery cable ( 0 dia. battery cable) to one head, and ground it to the frame.
The sender is on the right side of the radiator, stuck in the tank, inbetween the upper and lower trans cooler lines with a green wire (i think it's green)attached to it.
DO NOT TRY TO TAKE THE SENDER OUT OF THE RADIATOR. It is just a little blade of metal encased in plastic with a o-ring to seal it. What happens is , the tangs that hold this sensor in the radiator break off, and you need another sensor that nobody sells, and an o-ring nobody has a part number for.
(don't ask)
all you need to know is the wire needs to be grounded to make the light go out.
I will be happy to sell you a radiator that doesn't have a sender in it that's absolutely fine for $90

 

Going to start a new thread, so my issues won't keep Bryan from getting his sorted. Sorry about the hijack.