Originally Posted by G-force
I'm curious what thread sealant you were using and ws the cooler anodize? I install thousands of aluminum on aluminum NPT fittings every year in the automotive world and never had one gall as long as I am using Loctite 567 that has PTFE in it. I suspect that welded assemblies such as that oil cooler leave you with a much softer thread than say the heat treated casting or billet 6061-T6 piece I typically deal with. I really doubt they are able to reheat treat such assemblies after welding leaving you with a dead soft thread material.
Originally Posted by rvbuilder2002
I am curious as well.
Your second photo clearly shows use of a sealant similar to Loctite 567, but the first photo shows no indication of what thread sealant might have been used.
Indeed. It was a learning experience for me and reflected my inexperience at the time...
When I installed the first fitting with thread sealant (not shown), I was concerned with how much torque was required to clock the fitting per plans. The fitting very quickly accumulated significant torque prior to reaching the desired clock.
Then I executed the mistake: I decided to "test fit" the second fitting in the other port (the one with the ruined threads in the picture above) without sealant (I didn't want to have to clean and reapply sealant if I had to back out the fitting with sealant initially) to gauge the torque. When the fitting started to grind (with surprisingly little torque), I backed it out to find the damage shown.
I returned to the oil cooler instructions to find the following delineated at bullet 5:
Note: "Use only steel hose fittings to connect to oil cooler ports."
I then searched online to learn why Airflow might direct to use only steel fittings. And thus the educational
(and occasionally expensive) nature of building your own airplane took hold as I learned about "galling" for the first time.
Had I not foolishly attempted to temporarily position an aluminum fitting in an (very soft) aluminum port without sealant, I would not have learned about galling and might have missed Airflow's direction to use steel fittings.
Whilst I appreciate the RV-14's (and other models') plans stating to use aluminum fittings, and had personally seen three flying RVs with those fittings, I opted to follow Airflow's guidance and went with the steel fittings on my replacement oil cooler.