Fox Low Coolant Light Problem

Discussion in '1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-' started by normando219, Feb 25, 2014.

  1. 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?
  2. 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.
    jcgafford likes this.
  3. 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.
  4. i'm thinking about getting a new pigtail connector. maybe the old one is bad, corroded or something.
  5. 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.
  6. Mike,
    you are correct. unplugging the connector turns the light off.
    Mustang5L5 likes this.