Oh dear! How bad is bad? My 405 was flashing coolant low every time so I popped the bonnet and put a cupful of water into the reservoir. Oh no! It was the yellow cap Dynamic Response tank! Have not started engine, vehicle at home. Any advice gratefully received. Thanks

Ok, so now I have drawn all of the liquid from the reservoir using a syringe and short tube. It was dark oil at the top and clear water below, so probably water has gone down the tube, or is there some kind of valve at the end? Anyway, is it worth topping up now with the correct fluid and crossing my fingers that I’ve got it all out?

My son did exactly the same on his in a hurry, had to have it drained and flushed through three times to remove the contamination, although he did top his up with antifreeze!

Been fine since for him. 2013 Range Rover Autobiography 4.4 SDV8
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I echo Dave G's comments. Prior to my ownership mine had apparent been topped up with Ad-blu. The dealership flushed it several times, took them 3 hours. They said it was the 3rd one they seen. The two fluids had emulsified, so needed flushing.

As you’ve not run your engine and therefore the pump, you may have gotten away with sucking out the contamination. If that is the case, you may be able to get away with a single fluid change.

The funny thing is, that I’ve not noticed a difference before and after. It was however put to me that you’d only notice it with "spirited" driving.

Heard of this happening a lot! Why did JLR put that lid on it?

I would be wanting to flush the lot out ASAP as you know water is heavier than oil and some of that water you just know will go where you dont want it. Potential corrosion etc etc emulsifying and major loss of performance 2018 SE SDV8 4.4 Byron Blue

Thanks for your comments everyone, kinda nice to know I’m not alone in this silly mistake. Anyway, I syringed as much fluid out as quickly as possible, then removed the tank and cleaned it out, syringed liquid out of pipes also and used a vacuum oil change pump to draw more. I’ve now topped it back up with the correct stuff and all seems well, no fault codes and seems fine going around roundabouts etc. So I’m keeping my fingers crossed for having saved an expensive dealer bill! Thanks for all the input guys.

Hopefully you’ve been lucky. Give it a check in a week or so, depending on how much you use it, to check for emulsification.

Lucky man! Might i suggest you change the fluid after 100 & 1000 miles just to be safe?