Oil cooler failure and off field landing: Epilogue

A week ago my Zodiac had an oil cooler failure which caused me to do an off-field landing. I wrote about the event in this blog post.  That mishap turned out well enough with a bit of skill, luck and significant help from friends.


It has taken a week but I now know what went wrong and feel compelled to share the information.  The short story is “builder error”.  The longer story explains how subtle an issue can be.


When I installed my new engine I installed it exactly like the old one including using the same size and type oil cooler, mounted in the exact same way.  I up-sized the oil lines running to the oil cooler.  The new oil lines and fittings are substantially larger.  The purpose of this was to reduce the pressure drop in the oil cooler circuit.  That worked out very well.  However the new larger oil line fitting on the passenger’s side was making contact with the cowling.


How did I miss that?  It was all too easy.  It has to do with the way I install my cowling.  I mount the lower cowling with the screws loose, make necessary connections, verify clearances, look for stray tools loose wires etc, attached the top cowling with screws loose, center the entire cowling on the spinner and tighten all the screws.  I have done this about a zillion times in the past 4 years.  Centering the cowing on the spinner generally calls for lifting the entire thing a bit and then tightening the screws.  This brought the larger oil line fitting into contact with the cowling but I could not see that because the top cowling was in place.  I did not suspect it because it was never a problem before.


What the heck, it worked for 20 hours before the cooler fatigued and cracked open.



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Comment by Jonathan Porter on April 19, 2011 at 12:09am
Thanks for sharing.  We remove top and bottom cowling and inspect after the test flight and again after about five hours of flight to look for any 'ascending issues' - there are usually one or two things that get a tweek!
Comment by David Peterson on April 18, 2011 at 2:31am

Insightful and perhaps somewhat surprising (to me, at least!)

It just reinforces how little issues can manifest themselves as big problems, and also what an unforgiving environment aviation sometimes can be. I'm just glad things worked out well in your case and we're able to discuss this failure in detail and learn from your experience!


Comment by Stephen R. Smith on April 17, 2011 at 10:02pm

Today I worked on a new oil cooler mount which will hold the cooler about 3/8 of an inch further from the cowling.


Will it is true that I can not see inside the cowling with the top on, once the bottom cowl is in the intended position and screwed down, I can and will remove the top cowl to inspect.  This is what I will do from now on when modifying the placement or size of any critical component.


We live and we learn.  If we learn, we may live.



Comment by Bob Pustell on April 17, 2011 at 9:31pm

As the old Perdue add went, "It takes a tough man to make a tender chicken". Well, it takes a tough man to detail his own errors or problems in a public forum. Thanks for having the strength to share what you learned with us. Not everyone would have the nerve to do that, and it is appreciated.


I like Damon's idea about the boroscope type gadget for a new cowl installation, in order to look around in there. Based on your experience, Steve, we should consider using the boroscope to look around in there anytime there is a change in components, no matter how cut and dried it may seem. We live and learn.

Comment by Dr. Edward M. Moody II on April 17, 2011 at 2:02pm
I'm glad you managed to limit the damage to the oil cooler. There are so many sneaky ways that a more comlex aircraft can bite you.
Comment by Jim Belcher on April 17, 2011 at 12:02pm
Thanks for sharing this. It's the little things we miss that get us. This will help me pay more attention to those!

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