CactusMan said:
The garage are telling me it's only supposed to register half way on the dipstick. Apparently you fill the engine. Some of the oil goes to the dpf filter leaving half way up the stick. I've never known a car run this way.
I don't seem to have any signs of a leak so maybe they're right.
That is not (technically) correct.
Engine oil and "DPF oil" are two different things.
The lubricating oil in the engine can be anywhere between MIN and MAX. It can be on MIN, it can be on MAX...these are the specified MIN and MAX quantities that engine needs to operate without damage to your engine. Anything less or more will cause damage.
If the oil level is between MIN and MAX then it is ok. If the level moves down over short duration - time or mileage - then you have an issue and will require investigation.
DPF oil used to be fitted to older Peugeots/Citroens (called EOYLS) and was a small pouch of sticky oily liquid that was injected into the Particulate Filter on diesels and was used as a catalyst to burn off the sooty exhaust particles and containments. Your HDiBlue uses a more modern variant of this called AdBlue which can be maintained by the owner and is a blue liquid held in a tank under the rear spare wheel well. The fluid is injected into the exhaust again to catalyse pollutants and particulates.
If the Engine oil was injected and used in this instance you would likely have a very smelly and smoky exhaust amongst creating other issues.