I recently posted a photo of the cracked oil cooler box on my IO-550 Legacy.  The reason I had the box out was that I was adding the oil cooler door.  Like Douglas, I did not install the oil cooler door when I built my Legacy.  First flight was a year ago and my oil temperatures were fine during the summer, but with winter weather, the oil was too cool.  On a recent flight the oil was down to 130°F.  Since I was doing my first annual inspection, I figured it was the right time to install the oil cooler door.

 

That involved removing the oil cooler box, which I needed to do anyway because of the crack, adding a piano hinge and the door, and installing the control cable in the cockpit.  I work pretty slowly and spent the better part of two days doing this. 

 

By the way, the TCM shop manual for the IO-550 specifies 170°F as the minimum oil temperature for cruise.  I don't know, but I think that is based on heating the oil enough to drive off water, which enters the oil as a product of the combustion process, and not on anything related to the lubricating property of the oil.  (TCM specifies that you can run 100% power with oil temperature of only 100°F on takeoff, so 100°F oil must provide adequate lubrication.)

 

Dennis Johnson

Legacy, just completed first annual inspection