Coolant warning / no heat

[DarronCarnall]

Amber coolant warning light has come on and off tonight with the temperature needle suddenly dropping from 90 to 80 but returning as quick as it dropped. Happened on and off for the 10/15 minutes drive. Had been in some traffic but been on empty road for good 5 minutes. Just been back out to check and the heating selection lights up but nothing comes out.

2014 C220 CDi Auto Sport Coupe

Any thoughts?

 

[Phil1968]

Check your coolant level?

 

[DarronCarnall]

Check your coolant level?

Thanks for the tip .

Yes, coolant was ever so slightly down. Topped up but still no heat. Car gets to normal temperature….will have another look in the daylight

 

[Diesel Benz]

This is not for a Mercedes but many of them are equally made:

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[DarronCarnall]

Can’t see into the coolant tank to see. Started ok this morning and when cold fans work, as the car gets warmer the fans slowly loses heat and stops functioning….

 

[Gbrowncls55]

interior or exterior temperature sensor, but could be lots of things. Best get it on STAR rather than chasing the fault.

 

[DarronCarnall]

Had Greenflag out to look at it, saying it’s most probably the internal heater motor.

 

[Diesel Benz]

Can’t see into the coolant tank to see. Started ok this morning and when cold fans work, as the car gets warmer the fans slowly loses heat and stops functioning….

Previously I thought the HVAC fan was fine, if the fan does not spin, the coolant level or silica leak would make no difference. As above, if the motor does not spin, it is the heater motor, the regulator or sometimes the HVAC control unit.

 

[Justintyme]

Are the coolant water jackets to the radiator very hot to the touch? If not, I'd be thinking thermostat. ( one will be cooler that the other of course...the one feeding back into the engine, and I think that's the lower one )

 

[mcgee]

@DarronCarnall I'm presuming the internal heater motor suggestion was based on a diagnostics scan by Greenflag? If not, if you can get hold of a scanner, that would be my first port of call to get to the bottom of it as quickly as possible.

 

[suty455]

I would say check the coolant again you may have been lower than you thought and its got an airlock in the heater matrix, the sudden drop in temp could have been either a stuck open Stat or a sensor sitting in a void due to lack of coolant, get it warm and the park it so the radiator/ exp[ansion is the highest point and let it cool down any air should work its way to the high point, its probably not a problem on newer cars but cars of old were plagued by this type of issue usually because the matrix was higher than the rad and air always rises.
The heater motor will not normally run until you are up to temp, if you hit the windscreen button however the fans will work irrespective if the fans work its not the blower .