Hi I do not mind comments at all, I freely admit that much of what I have said is speculative based upon little data.
Now as regards the mixing of DPX and EOLYS I will speculate that not only do I not know exactly what happens when these products are used together or interchanged BUT nor does PSA.
Why do I say this? let me explain.
PSA did not develop the original DPX system that was largely based upon work done by BOSCH, now did BOSCH specify the operational requirement of DPX or was the liquid an "off the shelf" product? Actually it makes little difference as the whole system Particulate Filter Fluid Engine Injection Parameters etc. would have been "tuned" to perform to an agreed specification and supplied to PSA as a package. Somewhere within the contract for this would be words along the lines of "if built to the specified requirements and operated with the specified fluids then the system will work as advertised, however we cannot be responsible if the system is changed or other than approved components are used"
PSA would in all of its documentation training etc maintain the same line, they have to it's one of the ways that they can avoid expensive litigation, standard operating procedure for any manufacturer
Now fast forward a little BOSCH or maybe some one else comes up with an improved system same thing as before build it like this run it using this fluid and it will work.
The thing that PSA won't do is to establish what happens if either components software or fluid are mixed between an early system and a late system, PSA likely don't have the facilitys to do this on their own account and if they go back to BOSCH and ask them to do that work then BOSCH will ask them for a lot of money to do the research. Why would PSA or BOSCH for that matter spend that kind of money doing research which from their perspective has no practical value?
It is far more sensible for PSA to take the line that the fluids are not compatible or no it is forbidden to run an engine with software for DPX42 on Eolys 176, they don't know how well it will work or even if it will work at all but they do know that it will affect the emission certification of the engine so they have to take the line they do.
Frankly I wouldn't believe anything PSA said on this issue, like I said I don't believe they know. For example " Eolys 176 has been designed to produce less ash post burning " again as a top level statement I believe that, but just how much less ash? Looking at the difference in injected quantities between DPX42 and 176 my gut feel is that the major improvement in filter life comes from less cerium content rather than reduced ash production, my gut feel on that statement is that the reduction of ash is a minor component of the improved filter life. Actually thinking about that further as I remember from the original BOSCH write up on the system operation they claimed the major source of ash was from residual lubricating oil burnt in the exhaust not from the combustion of modern low sulphur diesel.
According to PSA, the fluids are fundamentally different and so they are incompatible.
Well for reasons outlined they would say that, "Fundamentally different "is I suspect a bit of hyperbole given that both fluids work in systems whose operating ethos is essentially the same I would be surprised if they were fundamentally different. Would be interesting to ask PSA if they could provide results of test that prove they are incompatible suspect that you might be waiting a long time for that as well
Actually even if they were fundamentally different that doesn't automatically make them incompatible.
PAT fluid can't say I am surprised to do detailed trials is expensive and for reasons of emission certification could open a can of worms which could get very expensive. My feeling is that they could probably show that in terms of filter life it approximates the approved fluids and that at the end of the day is going to satisfy the vast majority of their users. If it achieves that the customer base is not going to complain so they can continue to maintain a low profile.
The only real way to prove some of these things is for some one to do it until then it is speculation, thought I might do some of it but my 2001 2.2 is going to be sold on so I probably won't