C8 underside view, what is this case thing please!

[PeteC8]

Had an exploratory crawl under my "new" 2004 C8 diesel auto, the purpose was to have a leetle look at the gearbox oil colour after 79k. Got distracted by a coolant weep from the very corroded webasto heater pipes, then noticed this object. Totally new to all this here modern stuff, could some kind soul enlighten me as to its function?

Many thanks in advance, Pete.

[wheeler]

Looks like your Eolys reservoir to me.

[PeteC8]

Looks like your Eolys reservoir to me.

Said I was new to this modern stuff!! Never heard of Eolys until this moment, I will now educate myself as to what if anything I need to do to replenish it!

Many thanks for the lead!

[GiveMeABreak]

It's your DPF additive tank. It uses the Eolys fluid to dose the diesel tank with a metered amount of additive whenever you put diesel in the car. The additive reduces the temperature required for regeneration of the particle filter from about 550 °C to about 450 °C.

When it need topping up, you should get a message telling you the additive is low. It should then be topped up using a gravity feed with the correct additive fluid (there are lots of types and some cannot be mixed) and the engine ECU or the additive ECU on earlier vehicles will need to be reset once it has been topped up, which requires a dealer-level diagnostic tool.

This is an older video for earlier systems, but shows the regeneration operation:

[wheeler]

Said I was new to this modern stuff!! Never heard of Eolys until this moment, I will now educate myself as to what if anything I need to do to replenish it!

Your in for a treat
Good luck when it comes time to top it up. Early systems were very problematic when it comes to resetting it after refill & sometimes requires replacement of the additive ECU.

[GiveMeABreak]

Yes, Pete has the DW10ATED4 110 engine, so shows up with the separate ECU for the additive function, so these where typically problematic to reset as Wheeler says. I had no issues on my MK II C5 with the separate unit, so it's not a guaranteed fail, thankfully.

[PeteC8]

Said I was new to this modern stuff!! Never heard of Eolys until this moment, I will now educate myself as to what if anything I need to do to replenish it!

Your in for a treat
Good luck when it comes time to top it up. Early systems were very problematic when it comes to resetting it after refill & sometimes requires replacement of the additive ECU.

Thanks! I'll sideline that one and move onto the matter of linking out the webasto as the pipes are 'orribly corroded...

Followed rapidly with a dash of gearbox...

[PeteC8]

It's your DPF additive tank. It uses the Eolys fluid to dose the diesel tank with a metered amount of additive whenever you put diesel in the car. The additive reduces the temperature required for regeneration of the particle filter from about 550 °C to about 450 °C.

When it need topping up, you should get a message telling you the additive is low. It should then be topped up using a gravity feed with the correct additive fluid (there are lots of types and some cannot be mixed) and the engine ECU or the additive ECU on earlier vehicles will need to be reset once it has been topped up, which requires a dealer-level diagnostic tool.

This is an older video for earlier systems, but shows the regeneration operation:

Thanks for the explanation. My head got fried by all the 3 letter abbreviations when I was trying to determine how it worked that was different to the Adblu system!
I now understand

[GiveMeABreak]

Yes the Selective Catalytic Reduction (SC) system treats the NOx in the Cat using UREA (Adblue), before the DPF Diesel Particulate Filter traps the particulate matter which it regularly regenerates to burn off the soot.

Earlier vehicles may just have a DPF, whilst later vehicles from about 2013 have both systems. They perform different functions and are totally separate from each other.

Here is how the later systems work, also referred to as Blue HDi.