My car’s warning system started flashing a few weeks ago warning AdBlue was running low.

I found an unopened 5l bottle I must have purchased well over 2 years ago when they were going cheap (why?) in Tesco. I probably bought 4 or more as we have 2 diesel cars. Like many I suspect we did much less mileage during the pandemic.

I’d never really considered it before but does the stuff really ‘go off’ if unopened or in the AdBlue tank?

After a search I’ve seen estimates of it deteriorating 18 months to 3 years after manufacture.

I can’t see any manufacturing or use by date on the 5l bottle, nor any warning that it should be used within a certain timeframe. For the sake of a few quid however I’ve just topped up with some ‘new’ AdBlue, prices seem to be almost double for the same brand (Redex). Although it’s technically only concentrated urea, I’m not sure again after a search it’s environmentally safe to simply pour it down the loo or into a drain.

Furthermore, it seems that unless you’re doing very high mileage it would be better to top up ‘fresher stuff’ in smaller quantities more frequently than risk the AdBlue in the AdBlue tank deteriorating over time.

I am unaware of deterioration of AdBlue upon storage, though (as a chemist) I would be surprised if a pure solution of urea kept clean and in the dark (or opaque bottles) at ambient temperature were to suffer any significant decomposition in only a couple of years. However this is not something I have studied so is not definitive. Once transferred to a vehicle tank there may be greater potential for contamination and decomposition.

As for disposal, given that urine normally contains somewhere in the region of 1-2% urea (about 1/20th of the strength in AdBlue), I would not expect any adverse effect whatsoever on the sewage system from the odd bottle of AdBlue put into it, though if you live in a location where sewage volume is likely to be small it would probably best to limit the quantity at any one time, spreading 5 litres over several days and with plenty of water to dilute it.

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Those were pretty much my thoughts - the plastic container is not opaque but a sort of off-white similar to those large containers for screen-wash.

I can’t actually remember the last time I topped up before today so will dispose of that old 5l ‘just in case’ as some sites say that if the urea has degraded there’s a risk of damage to the catalytic converter. If this is the case I find it surprising there are no clear warnings that the stuff should be used within a certain timeframe even if unopened.

My advice would be to dilute it 20:1 and add to your compost … as an aside I have anecdotal evidence to suggest that ‘compost enhancer’ is best when fresh!


Great idea!

What a great suggestion. It would probably be quite acceptable less dilute, certainly 1 to 10.


It deteriorates with time and crystallizes, causing the ad blue injector to clog and maybe worse. It cost me $400 for running expired Ad Blue, to have the tank and the rest of the Ad Blue system cleaned out.


Was this risk something you were unaware of until a problem arose?

AdBlue has a shelf life of around 18 months when stored between 0c and up to around 35c.

Being of a Corrosive nature it must be disposed of in a safe manner at an approved disposal point.

It should be kept in the supplied container and ensure that no AdBlue or AdBlue container is used for topping up cooling systems as it can cause extensive engine damage.


No wonder urine was used to cure leather …, and @Project-G ‘compost accelerator’ also deposits crystals if it’s not used fresh.

Aqueous solutions of urea slowly decompose to ammonium bicarbonate and ammonia.


Now why did I not think of my chemistry background …?

Our car tells us that it can only run 100km until it runs out of ureum. I wonder if it still starts in 2 days time.

If it’s run out then AFAIK the vehicle computer will refuse to start the engine.

Hmm service is next week. I think I’ll run to the shop then to add a bit myself. Never done that before.

It’s fairly easy to do. I topped up at around 600 miles worth left having been prompted for weeks.

Some bottles have a supplied pipe/nozzle (eg Redex 5l) which fits into the bottle to allow relatively mess free topping up.

Our VW dealer did a ‘courtesy’ AdBlue top up on Mrs AC’s car when it was last serviced I think - are you likely to do 100km before the service? Could they do it for you, amount roughly based on what you expect to do annually (I suspect a lot of cars have ‘old AdBlue’ in the AdBlue tank if their owners did very little mileage during pandemic lockdowns.)

Might be worth checking the manual to see at what level the car will refuse to start just in case it won’t allow it to go completely empty (though I suspect they may flag the AdBlue tank as empty with a small amount remaining in practice).

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