The volume of the tank on your GLE SUV W166 is 8,5L or 24,5L.
In case the level of AdBlue® drops to the reserve level of 3.0L, which corresponds to a mileage of 1500 miles, the message “Add AdBlue® see instruction manual" will appear on the dashboard. The warning message disappears 1 minute after fill up if you drive faster than 10 miles/hour. If the level reaches its minimum, the message "top-up AdBlue® mileage: ...km" is to be seen on the dial switch indicating to you your remaining mileage.
As soon as you see the AdBlue® warning light, you should refill your AdBlue® tank so as to be able to restart the engine. If you do not fill up with AdBlue®, the message "top-up AdBlue® , restart impossible" is to be seen on the dial switch to fill up. Pour at least 3,5L to switch the warning off, turn the key in the ignition for about 60 seconds and then start the engine.
This information can vary on some vehicles of the same model in relation to the options chosen by the manufacturer.