Last night it dropped to -5 where I am, and this morning I put more washer fluid in and noticed the coolant level was under the minimum, maybe 5mm under.

I check the coolant during the milder weather and with the car cold the coolant always sits slightly above the minimum coolant. I've been running with the heat on obviously recently. Could it be a combination of the coolant just having reduced in volume due to the sub zero temps and having the thermostat open full?

Cheers.

4 hours ago, Nismex said:

...Could it be a combination of the coolant just having reduced in volume due to the sub zero temps and having the thermostat open full?

Asked, and answered...

1 hour ago, StephenFord said:

having reduced in volume due to the sub zero temps

of course when the coolant freezes it will most definitely increase in volume - it's the Titanic effect 😉

2 minutes ago, unofix said:

of course when the coolant freezes it will most definitely increase in volume - it's the Titanic effect 😉

Absolutely correct, when liquid freezes, it expands, hence why pipes burst in winter. I try my best but some days I'm really off my game! 

On 12/14/2022 at 7:12 PM, StephenFord said:

Absolutely correct, when liquid freezes, it expands, hence why pipes burst in winter. I try my best but some days I'm really off my game! 

To be really pedantic. Water contracts like most other materials when it cools,  until it gets to +4C, then it expands below that temperature.

It's the only liquid that is known to do this. I'm not sure what happens when water is mixed with anti-freeze.

 

21 minutes ago, Blatto said:

To be really pedantic. Water contracts like most other materials when it cools,  until it gets to +4C, then it expands below that temperature.

It's the only liquid that is known to do this. I'm not sure what happens when water is mixed with anti-freeze.

 

Correct and it does the same above 4C. The Rubber hoses will also expand and contract as they  react to the increase or decrease in pressure in the system as well and the liquid may also react to changes in Atmospheric pressure too.

Liquid bismuth also expands upon cooling. That, together with a very low melting point

is why it was used for printing type.

Well the temperatures are warmer, 5C and it still sits below the minimum line, it's only a smidge higher than where I marked it during the cold spell.

I'll take it into the garage tomorrow for them to advise I think. Can't say I am noticing any issues in the oil when I have a look, nor any leaks/smoke.