So, if the idea is to use steel where the result of failure is catasrophic, then how do you explain rubber tubing on the drain lines??? Are you implying that losing oil pressure in 20 minutes (and NEVER SEEING any warning indicators on a gauge) is better than losing it in 30 seconds from an oil line failure (where it will likely be indicated on the oil pressure gauge) ???

Matt,

 

I'm not implying any such thing.  I said that if you feel more comfortable with all steel fittings go right ahead, then there is no uncertainty.  In either of the cases you mention above, the oil pressure may not drop until there is no oil left to pump around.  Note that there is a restrictor in the steel oil pressure sensor fitting on my engine.

 

I have seen aluminum fitting used on other Lyc engines in the places I mentioned.  I have never seen aluminum fittings used in the other locations.

 

I can explain the use of the rubber tubing connectors as standard Lyc practice and because cylinder heads expand as they are heated - thus if complete hard lines were used they could be worked to failure. 

 

As another contributor noted, on a 320 with a rear mounted prop governor the hard high pressure oil line from the steel fitting near the front journal back to the governor is itself stainless steel - not aluminum.

 

Finally, many people have successfully used reinforced rubber lines for fluid connections in the engine compartment.  Of course, the recommendation is that they be changed every 5 years or fifty billion gallons, whichever comes first.  The 1973 Skymaster I flew had a brittle line failure in 1992 (about 2500 hrs TT) in lines that were manufactured in 1971, merely 21 years of use.  Luckily the fuel line failure was observed on the ground with the cowling off.  I learned from that experience and every flexible fluid line in my Lancair engine compartment is Teflon encased in SS braid and fire shielded.  Oh well, I traded weight and money for safety and no known life limit.