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Never Fill the AdBlue Tank to the Brim

Model: (Various brands) Various
Part: Checks and maintenance

Video tutorial

The video explains an important and little-known concept regarding the maintenance of the AdBlue system, which is not just a simple fuel tank, but a closed hydraulic circuit under pressure. This is drawn from a pump, sent to the injector on the exhaust, where only a tiny part is injected; the majority of the fluid returns through a return pipe.

If the tank is filled to the cap, the return fluid has nowhere to go, causing a dangerous increase in pressure inside the tank; moreover, the continuous circulation of the fluid raises its temperature. High pressure and high temperature can lead to damage to the tank itself, damage to the pump, and degradation of the fluid (which crystallises more easily when overheated).

The suggestion is to frequently top up with small amounts: do not wait for the tank to be empty, but do not fill it to the brim either; add 5 litres at a time to leave the necessary headspace for fluid circulation.


Posted on 29 March 2026 by ScegliAuto


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by ScegliAuto

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