Lycoming IO540 unknown fitting on back of engine
 

I've posted a top down and from left rear view of my Lycoming io-540 (van's purchase). If you look at the top picture, just in front of the oil filter is a brass fitting for my oil temp. The large red cap is for the tach which will be closed off. The blue 8d fitting to the left over the magneto is an oil cooler line fitting.
The one I can't figure out is the 6D male fitting (green arrow)(with red cap on)
thats coming up from directly below the breather tube.

Any suggestions. I've seen pictures of some other io-540s and this was a plugged off area. Is there a plug I can get somewhere?




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My Lycoming, that I bought through Van's, had a manual with it. In the back of the manual, they had accessorie case drawings of many different flavors and pointed out all of the connections. Have you looked there?

yep. Went through the manual. It isn't listed as an opening or fitting for the D engine
Tom

End of the main oil passage up from the pump. You have a choice about where to connect the line out to your oil cooler. Since you've chosen the other location (the blue -8 fitting below the filter assembly), the mystery location gets (1) a plug and crush washer if you have an oil filter adapter with vernatherm, or (2) a plug, crush washer, spring and plunger if you have an oil screen (which ain't likely these days).

See the illustration here:

http://www.vansairforce.com/communit...9&postcount=14

Unknown fitting
 

Tom,

My Vans supplied IO-540 had the same fitting. After consultation with an engine repair shop over here in Oz, we installed an AN929 CAP flared tube fitting over the 6D male fitting. No leaks or issues in 35 hours

cheers,
Ron
VH-XRM
flying in Oz

You guys are great. Thank you.

Lycoming plug and gasket. $44 us
ACS AN929 tube cap- $3.21 including shipping.

AN929 cap ordered and on its way :^)

Tom H.