Oil Leak C-85

[Chrisgoesflying]

Would love to pick your brains about this.

Two weeks ago, I went flying and noticed that the oil pressure was slightly lower than usual. Still well in the green, just above 30 psi in cruise. Flew for about an hour and then landed. While taxiing at just over 1,000 rpm, the oil pressure was really low after the flight, barely touching 20 psi. It’s normal to have lower oil pressure after flying, but usually it doesn’t get that low.

Today, I wanted to go on another flight and noticed there was oil dripping out from the front of the engine, right below the prop (see photo, scroll to the second photo for close-up: https://imgur.com/a/jfuHmsH). It wasn’t a whole lot, but I’ve never seen oil there. I cancelled the flight but ran up the engine. First run up, all was normal with oil pressure close to 40. After the run up, I idled at 1,000 rpm for 5 minutes and oil pressure was just under 30. Next run up, oil pressure came up again to about 35. After pulling power back to 1,000 rpm oil pressure went down to about 20. Last run up, oil pressure went up to just over 30. Then back to 1,000 rpm and oil pressure went down to under 20 psi.

I parked the plane, went for a bite and then back to the airport. I looked at the same spot and saw some oil dripping there again.

For reference, on the last flight two weeks ago, OAT was around 22 degrees. Today was about 24 degrees. I’m running Aeroshell w80 but topped up with w100.

The engine was rebuilt in December with all new gaskets and a bunch of other new parts. Ten hours after the rebuild, the mechanic re-torqued all screws and changed the oil again. That was in mid January. Since then, I've flown the plane about 20 - 25 hours (would have to get the logbook to know exact numbers) with no further maintenance.

It's a C-85 12F engine with a spin-on oil filter pulling an Ercoupe with me and my wife all throughout Canada (and hopefully soon the U.S. once the border opens).

 

[wanttaja]

Sounds like it might be the nose seal around the crankshaft. It can be changed out without disassembling the engine, though you might have to take the prop/spinner backplate off. The seals aren't that expensive.

I was getting a lot of oil on the front of my C-85 a few years back. New seal fixed it, took the A&P about 10-15 minutes (no spinner).

However, mine never actually produced oil dripping, so it sounds like yours is in worse shape. Your seal may have gotten disturbed.

Ron Wanttaja

 

[MBDiagMan]

Are the case bolts tight?

 

[DFH65]

The o-200 manual says minimum idle oil pressure is 10 psi.
http://www.seagullaviationservices....INENTAL-C75-C85-C90-O-200-OPERATOR-MANUAL.pdf

 

[Dan Thomas]

Cooling airflow does weird stuff around the front of the engine. That oil could be from the crank seal, from that cover over the vacuum pump drive, or from either of two oil gallery plugs on the front of the crankcase. If the leak was causing an oil pressure drop, there should be vast amount of oil everywhere. A real mess. An EPA-level mess.

The oil pressure will fall as the oil heats up. It's normal. But if it's erratic there might be some contaminant under the pressure regulator piston seat, or an internal leak, possibly at the accessory cover gasket. If that blows out internally you lose oil back to the crankcase. The oil pump in the small Continentals is barely adequate and it doesn't take much of a leak to drop the pressure.

 

[Chrisgoesflying]

Sounds like it might be the nose seal around the crankshaft. It can be changed out without disassembling the engine, though you might have to take the prop/spinner backplate off. The seals aren't that expensive.

I was getting a lot of oil on the front of my C-85 a few years back. New seal fixed it, took the A&P about 10-15 minutes (no spinner).

However, mine never actually produced oil dripping, so it sounds like yours is in worse shape. Your seal may have gotten disturbed.

Ron Wanttaja

You're the second person who suggested the nose seal so definitely worth checking. Glad to hear the engine doesn't have to be dissembled for this as we just went through this late last year.

Are the case bolts tight?

That I don't know. I know the mechanic tightened all bolts ten hours after the rebuild. I'll have my mechanic check on that.

The o-200 manual says minimum idle oil pressure is 10 psi.
http://www.seagullaviationservices....INENTAL-C75-C85-C90-O-200-OPERATOR-MANUAL.pdf

Absolutely right. However, I guess the benefit of plane ownership is knowing the plane inside out. If this was a rental that I occasionally fly, I would have flown it as everything was in spec as per checklist/manual. However, having flown this plane for 60+ hours in the past year in scorching hot as well as freezing cold weather, from the coast to mountains to prairies, I never saw this kind of behavior, hence I'd rather play it safe.

Cooling airflow does weird stuff around the front of the engine. That oil could be from the crank seal, from that cover over the vacuum pump drive, or from either of two oil gallery plugs on the front of the crankcase. If the leak was causing an oil pressure drop, there should be vast amount of oil everywhere. A real mess. An EPA-level mess.

The oil pressure will fall as the oil heats up. It's normal. But if it's erratic there might be some contaminant under the pressure regulator piston seat, or an internal leak, possibly at the accessory cover gasket. If that blows out internally you lose oil back to the crankcase. The oil pump in the small Continentals is barely adequate and it doesn't take much of a leak to drop the pressure.

Definitely no EPA level mess, just a few drops from that part of the engine shown on the photo here: https://imgur.com/a/jfuHmsH
Oil pressure drop is still within specs but not how it usually performs which rings my alarm bells. It's also not erratic. I didn't fly it yesterday as the oil pressure was lower after each run up by quite a bit, but last time I flew the plane two weeks ago, once in cruise, the oil pressure was stable, albeit lower than usual, but still well inside the green. Having said that, it was only an hour flight so could it have dropped if I went on a three hour cross country (which I planned on going on yesterday but ultimately cancelled), that I don't know.

 

[MBDiagMan]

Yes, 10 PSI hot is not, in itself, alarming, the fact that an oil leak presented itself at the same time is what makes me want to investigate.

 

[tonycondon]

Any noticeable drop on the dipstick?

ON my C-85-12F (Cessna 120) the cruise PSI is right around 30 and once warm it will be down in the 10-15 range idling after landing. I run Philips 20W50.

 

[Chrisgoesflying]

Any noticeable drop on the dipstick?

ON my C-85-12F (Cessna 120) the cruise PSI is right around 30 and once warm it will be down in the 10-15 range idling after landing. I run Philips 20W50.

Some drop, but nothing alarming I would say. Maybe it is fine and I'm overreacting? Someone once told me, with these old a** planes and engines, the only time you should be worried is when you don't lose oil because it means you're out of oil.

Is it normal to see oil here?