Coolant light used to come on dim or bright and then go off, on it sown. Coolant level is fine. I replaced the sensor and everything worked fine. Wife drove in bad traffic and light came back on. Coolant OK still and temperature never got much above 80 on the gauge. Ideas?

In a recent post, either Donnie or Steve said to check for corrosion in the contacts of the reservoir coolant level sensor.

Sixto
91 300SE
87 300SDL
83 300SD

True. Usually its a corrosion problem.

Try some electrical contact cleaner and a stiff brush. The problem should go away.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car