My FFRR 4.4 nearly overheated today, rather ironically. I think it got a bit chilly overnight, and the radiator partially froze up. I was getting no heat from the vents either. I pulled over to let it cool down, then restarted it, and started to get some heat. It was still going up near the red zone before falling though, so I gently limped on to the Indy, where I was headed anyway due to the front door locks being frozen solid.

I've been getting coolant level warning bongs despite the level being fine, so I concluded that it would be a good idea to replace all of the coolant and get it replaced to factory spec, and hopefully it will be a lot more frost resistant, and also get rid of the false warnings.

I'm wondering if it was particularly cold here, I think it may have gone down to -15.

Cheers,

David Range Rover-less at the moment - Pining!

The coolant level sensor also checks the "weight" of the fluid ie the mix of antifreeze in there. If it is less than around 60/40 you will get a message on the dash. As per your owners manual

Also the temperature gauge gets its feed from the temperature of the coolant - if the coolant isn't moving due to the rad being flowing then this wont be able to give an accurate reading. So although you may have got to 3/4 on the gauge, more likely you were well into the red.

Fingers crossed you haven't done any serious damage by continuing to drive it (which I really cant fathom why you would do this when a replacement engine is going to cost half the value of the car)

Coolant should be changed every 2 years to keep the antifreeze mix effective. Personally I change it yearly to avoid sludge. 

I had the same last week.
I had it drained down and refilled no probs since. 15MY SDV8 Vogue SE