# Coolant sensor

**URL:** <https://community.cartalk.com/t/coolant-sensor/41109>\
**Category:** Maintenance/Repairs\
**Tags:** mercury, mystique\
**Created:** [December 21, 2009, 8:28pm UTC](https://community.cartalk.com/t/coolant-sensor/41109 "2009-12-21T20:28:25Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![mlaw66](https://avatars.discourse-cdn.com/v4/letter/m/c77e96/32.png) [@mlaw66](https://community.cartalk.com/u/mlaw66)\
**Post date:** [December 21, 2009, 8:28pm UTC](https://community.cartalk.com/t/coolant-sensor/41109/1 "2009-12-21T20:28:25Z")

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The coolant sensor light in my 6 cyl. 98 Mercury Mystique stays on all the time even though the coolant level is full.  
  
  
  
 Can I fix it or do I need a new sensor??

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**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\
**Post date:** [December 21, 2009, 9:32pm UTC](https://community.cartalk.com/t/coolant-sensor/41109/2 "2009-12-21T21:32:34Z")

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Unplug the coolant level switch connector to make sure the connections are clean. If that doesn’t solve the problem, then most likely the coolant level switch requires replacement.

Tester

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**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://community.cartalk.com/u/GreasyJack)\
**Post date:** [December 21, 2009, 10:10pm UTC](https://community.cartalk.com/t/coolant-sensor/41109/3 "2009-12-21T22:10:50Z")

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Where are you checking the coolant level? If you’re just eyeballing the plastic overflow reservoir, the coolant level can still be low in the radiator itself (which is where the sensor is). A faulty radiator cap can cause this, as could blockage in the lines from the reservoir to the radiator.

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**Author:** ![cigroller](https://avatars.discourse-cdn.com/v4/letter/c/c68b51/32.png) [@cigroller](https://community.cartalk.com/u/cigroller)\
**Post date:** [December 21, 2009, 11:24pm UTC](https://community.cartalk.com/t/coolant-sensor/41109/4 "2009-12-21T23:24:30Z")

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If you check your coolant level on a regular basis - both radiator (while car is cool!) and reservoir, then you can safely ignore that light. Or replace the sensor.

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**Author:** ![mlaw66](https://avatars.discourse-cdn.com/v4/letter/m/c77e96/32.png) [@mlaw66](https://community.cartalk.com/u/mlaw66)\
**Post date:** [December 22, 2009, 12:24am UTC](https://community.cartalk.com/t/coolant-sensor/41109/5 "2009-12-22T00:24:24Z")

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The sensor appears to be in the plastic overflow reservoir??

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**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\
**Post date:** [December 22, 2009, 12:26am UTC](https://community.cartalk.com/t/coolant-sensor/41109/6 "2009-12-22T00:26:46Z")

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Yes. The coolant level switch is in the coolant reservoir.

Tester