Mystery oil leak

[baldesk]

After a 2.5 hours of flight last weekend I noticed a tiny amount of black oil streaming along the right nacelle cover. I popped off the covers and discovered what appears to be a leaking gasket from the oil pump but I wanted to post to see if anybody has had a similar experience. I’ll be grounded till I get a mechanic out to diagnose. Thanks.

2018 DA42-VI with Austro E4-C engines.

Worth noting my Austro serial numbers do *not* appear on the list of engines requiring oil pump overhaul.

In the photos linked below you can see two small oil stream stains below the pump.


https://share.icloud.com/photos/0YQtl5Y ... 99TLNzhGSQ

[CFIDave]

Your "mystery" oil leak isn't coming from the oil pump, it's coming from underneath the high-pressure fuel pump. The fuel pump is driven by a gear inside the engine that has to stay lubricated by engine oil.

I've had exactly the same oil leak (coming from the high pressure fuel pump) occur 3 times during the last year from my DA62's left Austro engine. The first 2 times, the service center replaced the high pressure fuel pump's rubber O-ring, which provided only a temporary fix that lasted only a few months before oil started leaking again.

So last week the shop (after consulting with Diamond Canada) re-installed yet another new O-ring, but also added "liquid gasket" sealant to the surface of the engine near the O-ring. So far, the leak appears to be fixed (I've only flown about 4 hours since the repair).

The fundamental problem appears to be that the O-ring is too small, allowing oil to escape around its edges. Diamond needs to specify a thicker replacement O-ring.

[baldesk]

Thanks for your very helpful expertise once again Dave.

[Karl]

Your "mystery" oil leak isn't coming from the oil pump, it's coming from underneath the high-pressure fuel pump. The fuel pump is driven by a gear inside the engine that has to stay lubricated by engine oil.

I've had exactly the same oil leak (coming from the high pressure fuel pump) occur 3 times during the last year from my DA62's left Austro engine. The first 2 times, the service center replaced the high pressure fuel pump's rubber O-ring, which provided only a temporary fix that lasted only a few months before oil started leaking again.

So last week the shop (after consulting with Diamond Canada) re-installed yet another new O-ring, but also added "liquid gasket" sealant to the surface of the engine near the O-ring. So far, the leak appears to be fixed (I've only flown about 4 hours since the repair).

The fundamental problem appears to be that the O-ring is too small, allowing oil to escape around its edges. Diamond needs to specify a thicker replacement O-ring.

We are having exactly the same issue with CD135.

[baldesk]

One data point I failed to mention in this thread, coincidentally (maybe not???), on the flight leading up to the discovery of the minor oil leak I needed to cross-feed 3 gallons from the left wing to the right engine (engine w/ fuel pump oil leaking). This was due to two different lineman independently filling the L and R wings tanks which resulted in a 3 gallon imbalance. Pure speculation, but maybe cross-feeding increases the pressure on the fuel pump that contributed to the leak. I rarely cross-feed for more than a gallon so thought it was worth mentioning.