Well look at the reservoir and see if the coolant is where it should be. There should be an arrow or line on it somewhere. On the SDL's you fill them to the seam.

When it gets colder they can just come on. The SDL's comes on at random times on the highway, will stay on for 10 minutes than go off. Replacing the switch didn't fix it. German electronic's.

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2006 CL500
2009 C300 4matic
1969 280SE
2023 Ram 1500
2007 Tiara 3200