I've been reading conflicting information on this. Anyone have experience know if it's bad for to fill the adblue tank to about 3/4 instead of full? If I buy 20 liters I end up wasting most of one of the containers, so I want to fill just 10L. It shouldn't be a problem right? I don't like being wasteful and I also don't like being stuck with chemicals I have to now dump safely. This way I also don't have to worry about filling too much as I've also read that filling all the way to the cap is bad too.
I'm also adding adblue anti crystallisation solution so am less worried about crystallisation (I'm also unsure how leaving air can cause crystallisation.. as this happens anyway for months as the tank slowly empties.. but that's a side point.).
I top mine up every 3 months or so.
I usually buy 15 or 20 litre containers and dose these up with Anti Crystallisation additive, so the mixture is just ready to add. They are good for storage for at least a year if kept in a garage.
To see the effect air has, all you need to do is spill a few drops out onto some plastic and it will crystallise very shortly.
I highly recommend keeping the tank reasonably full, but refer to your handbook as it may vary, but usually a minimum of 6 litres should be filled up (and also pay attention to the procedure after filling - with regards to waiting a certain time before switching the ignition on).
With regard to air, that's why the system reverses the pump shortly after you switch the vehicle off to suck back all the Urea into the tank to help prevent crystallisation that can lead to blockages in the supply pipe and injector - especially as the supply pipe won't be heated with the vehicle not running.
A search suggests Adblue is 32.5% urea dissolved in 67.5% water. When in air the water part evaporates leaving the urea behind as crystals. It is these that can cause blockages. The water seems to evaporate quite quickly if you spill a bit leaving the white crystals. Similarly, the crystals easily dissolve in water. In the Adblue tank crystals could form above the liquid level but when driving I guess the liquid splashes about so any crystals are more likely at the top of the tank if at all.
A search shows that at 32.5% strength it freezes at -11°C, other strengths are higher temperatures. At lower strengths it freezes at 0°C as water but at higher strengths up to 60% the freezing point goes up to 35°C.
And that's why I always keep mine topped up to lesson the chance of this happening with the combined anti crystallisation agent. Never had an issue to date.
