Slightly off this topic but, this morning I thought as the car has not been run for over a week and it was covered in snow,I thought I would start up and warm up the engine as well as putting some charge back in the battery as I need to do a food shop.Started first time but after a few seconds the coolant hi-temp light came on and then started beeping,first thing I thought of was coolant level.I checked it and it was dead on the “min” level on the header tank.I let it run for 5 mins and it was still on.So I put just enough coolant in to take the level to half way.Still flashing on dash.Stopped the engine and restarted, light had gone off.

    So my question for the team is:  has anyone any idea at what level in the header tank does the “Low coolant level” light come on ?

Mine did it yesterday morning and my coolant tank is brand-new with new antifreeze.

It measures the resistance on the sensor prongs inside the tank. These prongs are easily contaminated and give false readings. Especially when left stationary for a while. Weather conditions can also affect the sensitivity of the sensor (cold most noticeably) this has to do with the anti-freeze properties of the coolant. If it freezes and the coolant is not up to standard. It could damage the prongs. A new coolant bottle is required in that case. Same goes with contaminants (though you could try to rinse it out with a bit of brake cleaner as a dirty cheap solution to see if it fixes it.) If the problem returns its most likely due to contaminants like oil. And you should get your waterpump system / headgasket checked.

To be fair the prongs are garbage to begin with. I've entertained the idea to figure its exact resistance curve and to retro-fit a different bottle with a better sensor and to make an adapter harness and a custom bracket to fit it to the fabia. But simply Shorting the prongs is easier. until you fix what ever is broken and then replace the bottle. If only it was to get rid of the anxiety of that annoying long beep every time you start the car.

Edited 31 December, 20205 yr by Xsr

   Thanks for your replies everyone,I am aware of how everything on the cooling system works as I am a retired diesel engineer,I was just curious if anyone had played with a header tank to see where the low level alarm came on.

       Happy New Year to all of the forum members, and let’s hope 2021 is better for everyone

@maccy it'll be variable depending on the conductance of the coolant, which will vary with age and contamination and probably temperature. Also any deposits on the probes will likely change the situation significantly.  Using tap water as opposed to de-ionised/distilled water to dilute the coolant seems likely to affect things too.  

 

If it helps at all, my investigations suggest that if the resistance on the end of the loom connector (i.e. normally the probes in the coolant) is more than about 60 kilohms, a low level alarm is triggered.  Below that and it isn't. (I didn't get more exact than finding a 56k resistor didn't give an alarm, but a 62k resistor did, when used to 'short' the unpugged loom connector).

 

Measuring resistance between the pins of the tank connector while adjusting the level could give you some idea of what level this is for your coolant, with your probes. 

 

 

Aah,so it works on a resistance reading and not whether the probes are immersed or not .Thanks.