Fox Low Coolant Light Problem

normando219 · Feb 25, 2014

Problem with the low coolant light staying on on my 1990 Mustang 5.0. It has plenty of coolant, is not overheating, not leaking (the system has been leak tested twice - good) and I've replaced the sensor in the coolant overflow reservoir. The only thing I can see wrong is the reservoir cap will not tighten up. Have you ever seen this problem?

mikestang63 · Feb 25, 2014

This is a very common problem with these sensors. Check to see if it's stuck in the tube. Usually it's the sensors are corroded.
The tank has metal electrodes at the bottom of the sensor.

Remove the sensor then let the electrodes soak in vinegar and then use some very find sandpaper to remove all the crud on the electrodes until its clean. Hopefully when you put it back together, the sensor will now work. If not, most guys end up solderingthe wire from the two terminals of the sensor to turn the light off.

normando219 · Feb 25, 2014

hehe. thanks Mad Mike. it's a brand new and clean sensor. i tried cleaning the old one - didn't work. i like the idea to solder the electrodes though.

normando219 · Feb 25, 2014

normando219 said:
hehe. thanks Mad Mike. it's a brand new and clean sensor. i tried cleaning the old one - didn't work. i like the idea to solder the electrodes though.

i'm thinking about getting a new pigtail connector. maybe the old one is bad, corroded or something.

Mustang5L5 · Feb 26, 2014

mikestang63 said:
If not, most guys end up solderingthe wire from the two terminals of the sensor to turn the light off.

That would turn the light on permanently. Unplugging it will turn the light off. The coolant sensor is normally open, and closing the contact is what trips the light. Soldering would complete the circuit and turn the light on. Simply unplugging it prevents any contact from ever closing it.

Early 5.0 LX's did not have a low coolant light. They have the wiring, but no sensor.

normando219 · Mar 1, 2014

Mustang5L5 said:
That would turn the light on permanently. Unplugging it will turn the light off. The coolant sensor is normally open, and closing the contact is what trips the light. Soldering would complete the circuit and turn the light on. Simply unplugging it prevents any contact from ever closing it.

Early 5.0 LX's did not have a low coolant light. They have the wiring, but no sensor.

Mike,
you are correct. unplugging the connector turns the light off.

Mindseye007 · Apr 10, 2023

Mustang5L5 said:
That would turn the light on permanently. Unplugging it will turn the light off. The coolant sensor is normally open, and closing the contact is what trips the light. Soldering would complete the circuit and turn the light on. Simply unplugging it prevents any contact from ever closing it.

Early 5.0 LX's did not have a low coolant light. They have the wiring, but no sensor.

what does it mean when the low coolant light flashes on a 1991 LX FOXBODY COUPE 5.0 EVEN though it's completely full to the level in the bottle.....??

Mustang5L5 · Apr 11, 2023

Mindseye007 said:
what does it mean when the low coolant light flashes on a 1991 LX FOXBODY COUPE 5.0 EVEN though it's completely full to the level in the bottle.....??

Issue with the sensor in the bottle. Nothing else trips the coolant light. Must be an intermittent connection with the sensor or some other bad connection.

Mindseye007 · Apr 11, 2023

Mustang5L5 said:
Issue with the sensor in the bottle. Nothing else trips the coolant light. Must be an intermittent connection with the sensor or some other bad connection.

I will get a new one of these no?

https://lmr.com/item/LRS-10968A/90-93-Mustang-Low-Coolant-Sensor

Mustang5L5 · Apr 11, 2023

Yes, short of any wiring issues which is probably not the case, then you need a new sensor.

I would start by cleaning the contacts in the sensor probe tip and at the connector first and try that.

Fox Low Coolant Light Problem

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Fox Low Coolant Light Problem

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