Low Coolant Light
Thread Starter
Burning Brakes
Joined: Dec 2014
Posts: 1,038
Likes: 44
From: Pensacola Florida
Low Coolant Light
This little guy has been popping on and off since I bought the 89 last September. I've replaced it and the radiator but it still comes on and off, the level is fine and doesn't lose a drop.
Any ideas?
Rick
Any ideas?
Rick
Race Director
Joined: Mar 2015
Posts: 15,926
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My 94 did the same thing mine has two brass bleeders by the thermostat any air there will set your light off they are a pita and have to becarful not to get the opti wet I just jack up the right rear of the car as far as safe and fill the tank at the radiator cap and let the air bubble out worked great 
Last edited by antfarmer2; Apr 16, 2015 at 12:56 PM.
Racer
Joined: Sep 2014
Posts: 429
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From: Brooklyn, MI
My 94 did the same thing mine has two brass bleeders by the thermostat any air there will set your light off they are a pita and have to becarful not to get the opti wet I just jack up the right rear of the car as far as safe and fill the tank at the radiator cap and let the air bubble out worked great
Race Director
Joined: Mar 2015
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or use the bleeders as designed
Last edited by antfarmer2; Apr 16, 2015 at 01:36 PM.
Le Mans Master
Joined: Jul 2002
Posts: 5,818
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From: Alive and well in Burlington NC
Sounds like air bubbles in the coolant. There was a process used many moons ago called packing the coolant. Start with a cold vehicle, remove the radiator cap and fire it off. Wait for the level to drop (thermostat opens) then top it off. Let it run for a few more minutes. This next part takes a little finess, increase RPM untill the coolant fills the remaining area and cap the radiator. Later C4s have the valve on the housing to help bump the air out.
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Safety Car
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From: Poughkeepsie New York
Sounds like air bubbles in the coolant. There was a process used many moons ago called packing the coolant. Start with a cold vehicle, remove the radiator cap and fire it off. Wait for the level to drop (thermostat opens) then top it off. Let it run for a few more minutes. This next part takes a little finess, increase RPM untill the coolant fills the remaining area and cap the radiator. Later C4s have the valve on the housing to help bump the air out.
Drifting
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From: NE Ohio
2024 C4 of the Year Finalist - Unmodified
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Burning Brakes
Joined: Dec 2014
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From: Pensacola Florida
Advanced
Joined: Aug 2013
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Low Coolant Switch
There is a small sensor on the passenger side of the radiator. It has a single green wire going to it. Try to carefully remove the sensor and clean it. If you leave the radiator cap on, very little coolant will escape. Be careful not to break the plastic tabs holding the sensor in place.
If this does not cure the problem a new switch can be had from Rockauto.com for $16 plus shipping or locally from O'Rilley for $22 plus tax.
If this does not cure the problem a new switch can be had from Rockauto.com for $16 plus shipping or locally from O'Rilley for $22 plus tax.
Burning Brakes
Joined: Jun 2014
Posts: 1,020
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From: Connecticut
I am going to take a stab at this issue. Don't shoot me if I am way off as I don't have a book for this year car and I don't have this sensor on mine.
From the description of your problem, it sounds as if this sensor is a low voltage ground sensor. What I mean is; when the sensor "senses" water (sensor tip gets wet) it completes the circuit to a ground or pulls a high DC TTL mark to a low DC TTL mark (basically a one to zero). Hence the single wire sensor. If the sensor is dry, then it cannot ground or complete the circuit (DC TTL logic high mark or one) which then tells the computer to turn on the low coolant light.
Now, if the wire that goes to the sensor is damaged or even partially broken or frayed, then the low coolant light could light sporadically as the computer believes the sensor is not wet.
Again, this is a shot in the dark.
From the description of your problem, it sounds as if this sensor is a low voltage ground sensor. What I mean is; when the sensor "senses" water (sensor tip gets wet) it completes the circuit to a ground or pulls a high DC TTL mark to a low DC TTL mark (basically a one to zero). Hence the single wire sensor. If the sensor is dry, then it cannot ground or complete the circuit (DC TTL logic high mark or one) which then tells the computer to turn on the low coolant light.
Now, if the wire that goes to the sensor is damaged or even partially broken or frayed, then the low coolant light could light sporadically as the computer believes the sensor is not wet.
Again, this is a shot in the dark.