W124 Coolant low light staying on
 

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

There might be a leak if you have to top up so offen. Check your garage floor :)

Get a new sensor. Mine went bad, they are cheap and easy to replace.

Chris

If you aren't losing copious amounts of coolant and the tank level looks fine, it's definitely the sensor.

The contacts corrode over time. You can try to clean the sensor contacts, but it will fix the problem only briefly.

As BadBenz94 stated cheap and easy to replace...15 minute job.

I would also be concerned about frequent topping off of coolant, as that indicates that you may have a breach somewhere in the system...

Besides cooolant level sensor, it might also be a windshield washer sensor going bad. I had that happen in '97 SL, where the low coolant light was on, but coolant level and sensor was OK - only because the circuit is paired w/ windshield level sensor, I was getting the annoying low coolant light. Easy and cheap to fix.

Must be coolant sensor, I unplugged it and light went out, plugged back in and light flickered a bit then on constantly. Had to be carefuly with sensor plug that thing is very brittle. Wll order a part tomorrow. Thanks for responses

Hi,
What does it mean if when you unplug the sensor and the light stays on?
1997 s420.

Senders usually fail in the closed position
 

A sender will almost always fail in the closed position, a fail safe as it were...

Temp Senders are usually a wax type sender or bi metal in a wax or silicone filled bath.

Oil pressure senders are designed to fail in the closed position.

The flicker was the sender showing it was attempting to read and then failed closed-light on.

If you cooked it you may have breeched the head gasket. Check the oil for coolant or have the local shop run it thru the basic emissions test and see what the readings are. I found I had a head waterjacket to gasket failure and a wee warpage via this method after doing the top off deal for a month after my ex squeeze overheated the engine by idling in traffic with the AC set to Antarctic in August!

when you unplug the sender the lite stays on to tell you either it ain't working or the wiring just fried, either way failsafe to a definate error message via the low coolant light.

I have started to have the same problem on my 93 320E, the coolant level is ok and the temp is ok. Can someone please tell me were to find the sensor. My car is a RHD model.
I really do not not much about cars and engines but I thought I would just check also the hoses on the radiator, there are no leaks, the top hose feels squishy when I squeeze it but the hose comming out of the side of the radiator is hard as though it has a coil inside it. Is this correct please. Thank you for your help.

The sender is attached to the coolant reservoir tank. It is black, residing near the front lower area, just below where the minimum fill level should be. Wires attached to it will give you a clue as that is the only electrical part attached to the tank.

Thank you, do I need to worry about the hose?
Phil.