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Stories from our members...

Engine Oil Happenings by George Loegering rev 16 August 2003

Checking the oil level and for fluid leaks on our aircraft is about as interesting as looking for problems with the proverbial Maytag washing machine. It's really hard to get excited about the engine oil. Most oil leaks are extremely small even though messy. The engine, while apparently slowly bleeding to death from minor leaks, is usually not in any eminent danger except perhaps cosmetic; however, serious oil leaks can be catastrophic and really get your attention. It pays to be visually alert and alert to unusual smells in flight. Prompt corrective action may avoid serious consequences to your pocketbook, or worse, yourself if you make a precautionary landing and get the engine shut down before all the oil is gone.

My first encounter with a serious oil problem was observing a buddy's C-172 that took off, then returned, to find a loose oil cap. It was hard to believe how much oil had left the engine so quickly. My first encounter with an oil problem was with the A-35 Bonanza on a rebuilt engine break-in flight. I smelled fumes on climb out but attributed it to normal out gassing from new parts coatings. Once at break-in altitude with high power setting/speed the smell was not noticeable. All went well through the full regimen and I landed after about 45 minutes. My engine mechanic was waiting and he gave a rather vigorous cut sign. As I exited the aircraft oil was already dripping from several places along the fuselage bottom. All the oil save a quart or so was gone! Turned out he used an E-225 oil pump but the tank return pump was for the E-205. The return pump could not keep up so the oil over boarded.

The early Bonanza's have an electrically controlled propeller pitch change mechanism; however, later models and many other piston aircraft use hydraulically actuated pitch control. The hydraulic fluid used is the engine oil. Occasionally the oil or propeller mechanism lubricant is evident on the windscreen. Sometimes it is from the prop blade seal or the engine front seal. Once I found it was from five of the top half-case thru bolts being loose: a very unusual and dangerous place for an oil leak. One of my flying buddies experienced a massive failure on his Globe Swift hydraulic propeller with engine oil covering the entire windshield. Luckily, near an airport, he was able to make an emergency landing without damaging the engine (a no-brainer landing decision in this case).

Sometimes a low oil pressure indication is not necessarily indicative of an oil leak. The E series engines have a large cone nut on the left side of the accessory case that houses the oil pressure regulator. The regulator is basically a spring and an orifice. If a small piece of metal or other debris blocks the orifice the oil pressure can go to near zero. I had an engine with cermachrome cylinders that had a nasty habit of loosing a small bit of chrome to the orifice. I finally started carrying a 1.125 inch socket and learned how to clean the orifice myself if I was forced down at a strip with no services. My patience finally wore out when it occurred for the 6th or 7th time on a no return IFR departure. It was a sweaty 20 minute flight to the nearest VFR airport. All the cylinders were replaced with factory new, one of the cermachrome cylinders was the obvious culprit.

The E-series engines have a "dry sump" with a separate oil tank. There is a backflow valve that keeps the oil in a reservoir cooler tank but with the engine shut down it is common for the oil to migrate from the tank. You must check the oil immediately after engine shutdown to get an accurate reading. Adding 4 or more quarts after the engine has set for a week could result in a mess as the excess oil can be over boarded.

Sometimes we simply luck out because of good design. I once serviced the V-35 IO-520 engine oil and fuel in the evening for an early morning departure, California to Minnesota direct. This should have enabled a double check before engine startup but that didn't happen. I climbed out of Trinity Center at gross through a low overcast with no hope to return. I smelled hot oil but it seemed to dissipate as we reached cruise speed so I assumed since the gages were normal that I must have spilled a little the night before. I chastised myself for not having a good reference point but forgot about it until after landing. While waiting for my cousin to pick us up I checked the oil or at least tried! The cap/dipstick turned out to be on the hangar floor! My cousin and I visited a local auto salvage yard and found a good fitting cap with a rubber gasket. The oil consumption was minimal on that engine so we used a length of welding rod (kept in the baggage compartment) to get an OK calibration point. That together with another calibration point after adding a quart enabled us to continue until we recovered a factory dipstick.

Your engine oil may seem ho-hum but it is the life fluid for both you and your engine. Check regularly for all fluid leaks before flight and do not hesitate to make a precautionary landing if you see or smell oil or have an unusual gage indication. Low oil pressure with high oil temperature could suggest that there is insufficient oil to cool the engine. This in turn could suggest an inadequate oil supply which is reason to consider a precautionary landing. Being vigilant and taking appropriate action will keep your engine oil from becoming a major happening!