Help! 300e coolant light comes on in morning?

[Miles81_240d]

Hello all,

my 92 300e (2.6) has been doing an odd symptom as of recently- it appears that the amber "low coolant" indicator (I think thats what it is- has an icon of a radiator on it) has been coming on every other day, seemingly only after my car has sat overnight , only during the first 15-45 seconds of driving... Yet, I freak out and go check the resevoir, and it has plenty of coolant present... could this be a sensor issue of some sort? (is there a coolant level sensor?)
Odd, that it doesnt happen every day, just every _other day_ or so.. and only during the first minute or so of driving the car. The rest of the day, the light will never come on. Weird!

Any suggestions?

Thanks so much for any and all of your help!

Miles
92 300e 2.6 126k