Put this is the category of you don’t know what you don’t know…  The attached photo shows two fittings.

The top one (actually two) is from the bottom of a TSIO0550 oil cooler where it feeds the turbo’s (for cooling) - at least that’s what was on my engine and seems to reflect the diagram in the TCM manual.  The bottom one is functionally the same thing but is a single fitting that I got from a local hydraulic fitting supplier.

Is there a reason that TCM used two fittings when they could have got by with one?

It appears the original(s) might be brass and steel (plated).  I’ll re-check when I’m out at the hanger.  The new/bottom one is steel (plated).  Perhaps there is some issue with the steel fitting in the aluminum oil cooler housing (galvanic/seizing), or perhaps they intend the brass fitting to be softer when attempting to get it in/out (if it’s stuck), or ????

Anyone have any insight before I insert the new one?  I was going this way because I desired the shorter fitting for better hose clearance/alignment.

Also, some time ago, I replaced a 90 degree TCM fitting on the fuel pump with a 45 degree steel one.  Now, I don’t recall if the original was brass? and/or don’t know if that was a mistake for some reason.  I don’t recall anything in 43.14 regarding brass vs steel fittings in aluminum housings – but’s there’s plenty of stuff in there that I may have missed/forgotten.

Rick Titsworth