I was perusing the Velocity manual online (sorry, not a public site) and came across a statement with regards to AN fittings needing to be steel if they are situated ON the engine. This was in the context of the lycoming installation instructions, and plumbing the "per plans" oil cooler in the nose to the engine in the back.

The direct quote is "all fittings that are attached to an engine need to be steel fittings. Aluminum fittings are not acceptable." Its in bold.

Considering I am going to be sending the oil  into a fitting that is connected to an aluminum bypass block on the pedestal, in OUR (rotary)  situations is this a critical issue? And what is/was the rationale for not using AL fittings on the Lyc's? Dissimilar metals? Heat expansion stresses? Fatigue?

Dave