Hi,
First off, I am a big fan of wet vacuum pumps. They just wear out; they don’t destruct like dry pumps. That said, there have been many upgrades and improvements in dry pump technology during the last 10 years.
According to information I have a healthy wet pump should exhaust 20 to 50 cc of oil per hour. This converts to 0.67 to 1.69 fluid ounces. Although that doesn’t sound like much when one fluid ounces of 50 weight engine oil is heated to 180 degrees it will make a big mess if there’s a leak.
All wet pump systems are equipped with a oil/air separator which is designed to separate the and re-capture the oil in the pump exhaust and return it to the engine.
It’s not uncommon for air oil separators, especially small original equipment ones on older airplanes to get clogged up with carbon and crud. They should be removed and thoroughly cleaned at regular intervals.
I’ve also seen restrictions in the oil return lines from the separator to the engine.
Before I removed a pump I would check to make sure the air/oil sep is clean and open so oil can return freely to the engine.
There is a seal around the drive gear (it’s called a Garlock seal) that, if leaking will allow excess oil to be pulled into the pump. The part number of the seal on you Lycoming engine is part number STD-208. These cost under $7.
I would clean the air oil seps and the return line first.
Then I would check the Garlock seal.
If they’re good it’s time to send you pump for overhaul, or exchange your pump. Exchange prices are between $500 and $600 depending on whether it’s a Pesco or a Garwin pump.
Let me know what you find,
Best,
Steve
