But then the very few airlines that bought the PW-powered "dog" were not being very "wiley" even on "3".
The DC-10 with the Pratts was made available to those airlines who thought that it might be useful to have a common power plant with their 747 fleet.
Northwest Orient ordered them. They were originally designated as DC-10-20s by MDC but Northwest did not want to be behind those operators who had already ordered the GE-powered DC-10-30 and so it was that MDC were quite happy to re-designate the PW-dog as the DC-10-40 just to keep the customer happy.
Only NW and the Japanese bought the Dash 40 and it grossed out way below the Dash 30 and it also suffered from coked-up bleed valves just like its 747 equivalent.
You can always tell a Dash 40 by the fact that it has a "tulip bulge" on the intake to the centre engine.
The other piece of DC-10-40 folklore is that NW had the infinitely-variable flap setting system on the DC-10 removed and only had fixed flap gates.
For those of you who are not familiar with this particular piece of genius let me explain;
For every given runway and every possible meteorological condition there has to be just one exact optimum flap setting. Most aircraft just have some fixed flap settings available so all performance figures are a compromise.
Mr Douglas fitted the DC-10 with a generous amount of fixed flap settings but also had a large wheel (like an elevator trim wheel) which moved a hidden variable detent which was set on a vernier scale to the nearest 1/10th of a degree.
Such witchcraft was too much for NW so they had it removed! In later life they had to eat humble pie when they started to buy DC-10-30s.
They are now about the only major in the world (apart from Biman) still operating this wonderful aeroplane in the passenger role as far as I am aware.