W124 Coolant low light staying on

[Addbhp]

My coolant low light is staying on, after topping up with the proper 50/50 mix. Any ideas? Car is a 90 300e.
Started the day after sitting in an extreme traffic jam for 1.5 hrs where the temp creeped up to 110 (temp outside was about 20C/70F). So next day added additional coolant mix, light went out for a bit, then back on. So added a bit more, but light continues to stay on. Temp is now staying just above 80 which seems good.
I never did hear the fans come on during the traffic mess, but didn't have air conditioning on, as my interior fan isn't working. Not sure if that has any impact. Will get to replacing what I believe to the resistor under the blower motor when I have more time.
Mark