-- I usually like to avoid aluminum fittings on the engine altogether,
-- but at least avoid aluminum fittings that are built away from the
-- block by extensions, nipples, etc.  


I hear people state that we shouldn't use aluminum fittings on the
engine...

I don't get it - Lycoming uses many aluminum fittings on the engine.  
Why is it okay for them to do it but not us?  Is their aluminum
better?  Are the locations less likely to cause fatigue?  One person
tried to tell me the fittings could melt.  That would be very
problematic, since many of the engine and block components are made
of aluminum (or even lower melting point materials) and I would guess
that most of the engine would have melted by the time those fittings
melted.  

So oil lines near the turbo shouldn't be aluminum?  Well, there are
aluminum parts ON turbos (I don't know specifically about aviation
turbos, but I do know about race car turbos and older F1 turbos).  
The oil flowing through those lines can't be more than about 280
degrees - and aluminum can handle temps that are a multiple of
that (and the oil would act as a coolant to any radiated heat from
the turbo).

Aluminum fittings on my Lycoming (non-turbo) include:
* oil return / drains from cylinder heads
* prop governor fitting (the line is SS, not the fitting)
* breather hose
* dipstick housing (actually, I think it is plastic)
And I am fairly certain that the parts that come with an FAA
approved spin-on oil filter kit include many aluminum fittings.

I agree it is important to support the hoses and pipes that lead from
any fitting - but where is AL okay and where is it not okay?  Do the
engine manufacturers have any published comments on this?

Thanks,

Matt