Angier, et al,

 

Interestingly, I have a mix of fitting on my engine - some aluminum and some steel.  I had to believe that the engine builder knew what he was doing.  If there are problems with the sealing of steel flare fittings, remember that one can obtain aluminum cone washers that work quite well in sealing such connections.

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I asked John Schwaner at Sacramento Sky Ranch about whether or not to use aluminum or steel fitting on the accessory case for oil lines. He encouraged me to use aluminum fittings, saying that you get a superior seal between it (softer) and the steel fittings (harder) on the ends of his hoses.

He further indicated that steel to steel connections results in a higher incidence of leaks