Oilcoolerrepair Blog

Oil Cooler Repair

As part of my massive firewall forward upgrade I found a problem brewing with my primary oil cooler.  This was a problem created by a poor original installation.  Let me try to explain..

When the oil cooler is bolted in place, it is required to make a spacer that goes between each tab on the oil cooler.  That way when you tighten the bolts, the tabs on the oil cooler aren’t bent.  Oil coolers are aluminum and the tabs can’t take the compression loads, so the spacer absorbs this load and allows you to tighten things down.  But…  The aluminum spacer must have something to spread out the load on the oil cooler tabs.  Lets call it a bearing surface.  Normally this is done with a steel washer.  The steel washer does not wear like aluminum and spreads the load over a wider area.  Below in the first four pictures are an example of an installation without the steel washers in place.  What happens is the aluminum has so little “bearing surface” that it fails in a short ammount of time.  The result is the steel bolt (AN-3 in this case) starts to cut it’s way through the oil cooler.  As you can see in the pictures, it wasn’t far from cutting in to the oil cooler itself. This install had about 250 hours of flight time.

I fabricated a “doubler” for each tab on the oil cooler.  I don’t like that term, doubler..  But for lack of a better word I keep using it on all these fixes.  Because of the nature of this install it required flush rivits on the face of the oil cooler.  After that was completed I cut down the spacers to allow for steel AN-3 washers. (AN960-3L to be exact)  Even though they are thin, the purpose is served and will hopefully lead to many hours of flight.  See the final 2 pictures for the corrected oil cooler.