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Oil Leak


S3flyer

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I few weeks ago my oil was changed as part of my annual.  No issues for the first few flights.  Last week, I noticed a few drops of oil coming from the lower cowl of my Sting S3.  I decowled the plane and the only two places I saw oil was on the engine mounting frame and a few drops around the top of the seal of the oil filter.  I also noticed oil on the interior of the upper cowl near the oil filter.  Don't have an oil filter wrench so couldn't change that out and check.  Is it common to develop a leak after 5-6 flights with oil filter?  

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Did you check that the filter was hand tight?  If it was loose you could weep a little oil.  I also once had a slight leak at the point the oil pressure sender screws into, at the very front of the engine.  It was hard to find because most of the oil blew back and made it look like it was coming from farther back.  Tightening the fitting slightly fixed it.  

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42 minutes ago, S3flyer said:

Yup.  The filter was definitely hand tight as I could neither tighten or loosen by hand. My sender is on the firewall which is free of oil.

Mine's on the FW too, but was leaking from the taper fitting at the front of the engine on the other side of the hose, where the original sender was screwed in.  Just a place to check...

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  • 2 weeks later...

As I expected, the fix was quite simple while the cause was a bit interesting.  The magnetic plug was checked during my last oil change by a large Rotax shop in the area with no issues.  I flew 4 flights over the next couple weeks with no leaks.  I noticed a small amount of oil on my wheel pant at the start of flight number 5 but attributed it to an overfill of oil.  Before flight #6 I noticed oil again and decided against flying.

My local mechanic and I had much closer look this morning and it turns out the mag plug was about 1/16 turn wrench-loose.  The suspected cause was the safety wire that was taught but was attached such that the pressure would tend to loosen the plug.  We tightened the plug, redid the safety wire and did several runups with no leaks.  Weather didn't allow for a flight test.

 

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The magnetic plug is interesting since the plug itself is steel and this seals against the aluminum engine block.  To my knowledge, there is no copper or fiber gasket sealing this joint.  The sealing surface of the block must be absent of any nicks or imperfections or the mag plug will not seal and a slight oil leak will ensue.  If the imperfection is large enough, oil will leak sufficient to cause a streamer coming out from the cowl joint and continuing down the fuselage.  In the past, someone left a small gouge on the engine sealing surface on my CT.  I replaced two new oil filters, thinking the leak was coming from their seals, before I found that the mag plug was the cause for the leak.  I could refinish this to get rid of the gouge but instead, I use a old spark plug compressible metal seal ring and add a dab of hi-temp red silicone to this to seal my mag plug.

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