Low Coolant Light On
Thread Starter
Burning Brakes
Joined: May 2010
Posts: 941
Likes: 10
Low Coolant Light On
Took my 87 Vette out for the first time in 6 weeks. She has been getting paint, interior etc. It ran great. Temperature was in the low 90's. At highway speed, engine was running between 182 and 190. In the village with weekend traffic, engine temp went to 219 and cooled right down when I got out of the village. Drove her about 25 miles. I am really impressed with her handling.
Brought it home and parked it. A few hours later I went to move it in the shop. The Low Coolant light came on. I checked the radiator and it was full right up to the cap. The coolant overflow tank is half full.
Your thoughts on what is causing the Low Coolant Light to be on ?
Thanks
8Valve
Brought it home and parked it. A few hours later I went to move it in the shop. The Low Coolant light came on. I checked the radiator and it was full right up to the cap. The coolant overflow tank is half full.
Your thoughts on what is causing the Low Coolant Light to be on ?
Thanks
8Valve
Instructor
Joined: Aug 2009
Posts: 146
Likes: 0
From: Broadway Virginia
On my '88 I had a similar thing happen. It was not low, but it did have a bit of crud on the sensor which sticks into the radiator tank. The dealer removed the sensor, cleaned it off, and reinstalled. That fixed it until the next time it did it. The second time it was due to air in the system and not being packed/purged properly.
Thread Starter
Burning Brakes
Joined: May 2010
Posts: 941
Likes: 10
On my '88 I had a similar thing happen. It was not low, but it did have a bit of crud on the sensor which sticks into the radiator tank. The dealer removed the sensor, cleaned it off, and reinstalled. That fixed it until the next time it did it. The second time it was due to air in the system and not being packed/purged properly.
8Valve
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
Thread Starter
Burning Brakes
Joined: May 2010
Posts: 941
Likes: 10
8Valve
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
The sensor is just a piece of metal poked into the coolant. When the water drops below the sensor, it biases a transistor to turn on the light. When it comes on, the water pump is pushing enough water flow to compress the air out of the engine, and push it into the radiator. then the water level goes down.
In order to get that light to stay out, you have to "pack" the water.
First, let the car cool off untill it's dead cold as much as the temp of the day will allow. Get a jug of antifreeze, remove the cap, and put it near the right front marker light on the bumper.start the car, and remove the radiator cap, and pick up the jug. Rev the engine until you look in the radiator, ansd see the water level go down. add antifreeze to the top. do not let go of the throttle with the cap off, or the air in the system will push out the antifreeze you just added.
put the jug down, stick your finger in the coolant to determine it's warmed up, and then double check the level, and reinstall the cap.
let go of the throttle, and let it idle.
close hood, get on the freeway, and the light should stay out. If it doesn't, you have to do it all over again......let it cool off, etc.
If the light keeps returning, and the overflow bottle keeps making antifreeze, you have to do a little detective work.
1. check the hose that goes from the radiator to the overflow bottle. check the ends for cracks. if any, replace the hose.
2. see if you can rotate the hose on the nipples. if you can, replace the clamps.
3. check the cap. if the cap has been on the car for 3 years or longer, replace it.
4. check the radiator tube the hose goes on. if it's cracked, use JB weld to seal up the crack.
5. Check the overflow bottle for cracks, loose clamp, bad hose, etc.
The purpose of the hose and bottle and the cap is to seal up the water path from the bottle to the radiator. when the car cools down, the water contracts, creating a vacuum, drawing the water back into the engine... If the path is exposed to air, the water cannot be drawn back into the engine, and you get lower and lower on antifreeze until the low coolant light comes on.
I personally hate that light because it takes usually checking all the areas, and then some before it finally goes out.
Next year when I remove the radiator to clean out between the radiator and the air cond. condenser, the fight will begin all over again.
In order to get that light to stay out, you have to "pack" the water.
First, let the car cool off untill it's dead cold as much as the temp of the day will allow. Get a jug of antifreeze, remove the cap, and put it near the right front marker light on the bumper.start the car, and remove the radiator cap, and pick up the jug. Rev the engine until you look in the radiator, ansd see the water level go down. add antifreeze to the top. do not let go of the throttle with the cap off, or the air in the system will push out the antifreeze you just added.
put the jug down, stick your finger in the coolant to determine it's warmed up, and then double check the level, and reinstall the cap.
let go of the throttle, and let it idle.
close hood, get on the freeway, and the light should stay out. If it doesn't, you have to do it all over again......let it cool off, etc.
If the light keeps returning, and the overflow bottle keeps making antifreeze, you have to do a little detective work.
1. check the hose that goes from the radiator to the overflow bottle. check the ends for cracks. if any, replace the hose.
2. see if you can rotate the hose on the nipples. if you can, replace the clamps.
3. check the cap. if the cap has been on the car for 3 years or longer, replace it.
4. check the radiator tube the hose goes on. if it's cracked, use JB weld to seal up the crack.
5. Check the overflow bottle for cracks, loose clamp, bad hose, etc.
The purpose of the hose and bottle and the cap is to seal up the water path from the bottle to the radiator. when the car cools down, the water contracts, creating a vacuum, drawing the water back into the engine... If the path is exposed to air, the water cannot be drawn back into the engine, and you get lower and lower on antifreeze until the low coolant light comes on.
I personally hate that light because it takes usually checking all the areas, and then some before it finally goes out.
Next year when I remove the radiator to clean out between the radiator and the air cond. condenser, the fight will begin all over again.
Last edited by coupeguy2001; Jul 18, 2010 at 12:46 PM. Reason: spelling
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Melting Slicks
Joined: Nov 2007
Posts: 2,830
Likes: 147
From: Gainesville FL
Intermediate
Joined: Jan 2020
Posts: 27
Likes: 0
88 vette
The sensor is just a piece of metal poked into the coolant. When the water drops below the sensor, it biases a transistor to turn on the light. When it comes on, the water pump is pushing enough water flow to compress the air out of the engine, and push it into the radiator. then the water level goes down.
In order to get that light to stay out, you have to "pack" the water.
First, let the car cool off untill it's dead cold as much as the temp of the day will allow. Get a jug of antifreeze, remove the cap, and put it near the right front marker light on the bumper.start the car, and remove the radiator cap, and pick up the jug. Rev the engine until you look in the radiator, ansd see the water level go down. add antifreeze to the top. do not let go of the throttle with the cap off, or the air in the system will push out the antifreeze you just added.
put the jug down, stick your finger in the coolant to determine it's warmed up, and then double check the level, and reinstall the cap.
let go of the throttle, and let it idle.
close hood, get on the freeway, and the light should stay out. If it doesn't, you have to do it all over again......let it cool off, etc.
If the light keeps returning, and the overflow bottle keeps making antifreeze, you have to do a little detective work.
1. check the hose that goes from the radiator to the overflow bottle. check the ends for cracks. if any, replace the hose.
2. see if you can rotate the hose on the nipples. if you can, replace the clamps.
3. check the cap. if the cap has been on the car for 3 years or longer, replace it.
4. check the radiator tube the hose goes on. if it's cracked, use JB weld to seal up the crack.
5. Check the overflow bottle for cracks, loose clamp, bad hose, etc.
The purpose of the hose and bottle and the cap is to seal up the water path from the bottle to the radiator. when the car cools down, the water contracts, creating a vacuum, drawing the water back into the engine... If the path is exposed to air, the water cannot be drawn back into the engine, and you get lower and lower on antifreeze until the low coolant light comes on.
I personally hate that light because it takes usually checking all the areas, and then some before it finally goes out.
Next year when I remove the radiator to clean out between the radiator and the air cond. condenser, the fight will begin all over again.
In order to get that light to stay out, you have to "pack" the water.
First, let the car cool off untill it's dead cold as much as the temp of the day will allow. Get a jug of antifreeze, remove the cap, and put it near the right front marker light on the bumper.start the car, and remove the radiator cap, and pick up the jug. Rev the engine until you look in the radiator, ansd see the water level go down. add antifreeze to the top. do not let go of the throttle with the cap off, or the air in the system will push out the antifreeze you just added.
put the jug down, stick your finger in the coolant to determine it's warmed up, and then double check the level, and reinstall the cap.
let go of the throttle, and let it idle.
close hood, get on the freeway, and the light should stay out. If it doesn't, you have to do it all over again......let it cool off, etc.
If the light keeps returning, and the overflow bottle keeps making antifreeze, you have to do a little detective work.
1. check the hose that goes from the radiator to the overflow bottle. check the ends for cracks. if any, replace the hose.
2. see if you can rotate the hose on the nipples. if you can, replace the clamps.
3. check the cap. if the cap has been on the car for 3 years or longer, replace it.
4. check the radiator tube the hose goes on. if it's cracked, use JB weld to seal up the crack.
5. Check the overflow bottle for cracks, loose clamp, bad hose, etc.
The purpose of the hose and bottle and the cap is to seal up the water path from the bottle to the radiator. when the car cools down, the water contracts, creating a vacuum, drawing the water back into the engine... If the path is exposed to air, the water cannot be drawn back into the engine, and you get lower and lower on antifreeze until the low coolant light comes on.
I personally hate that light because it takes usually checking all the areas, and then some before it finally goes out.
Next year when I remove the radiator to clean out between the radiator and the air cond. condenser, the fight will begin all over again.
When doing these steps which you state. I suppose you do this with the engine cool?
I tried to let it warm first and well by time I could get the cap on it back up on me. I noticed on my the sensor clip was broke and it leaked so I replaced it as well the cap.
When the car is cool i rev the engine to 2500 rpm top it and put the cap on bring it back down to idle and let it warm up and all should be good correct?
The low coolant light used to only come up if i hit the gas a bit or took off a little fast . Now since I changed the sensor and the cap it seems to come on when idle. Thanks
