Oil pressure lose - 1948 C-170 w/ C-145, 500 hrs SMOH

[swebre]

Folks,

Need some help...

Flying yesterday in smooth air @ 10,500. Throttle to the wall, slightly rich, 2480 rpm, oil pressure showing 50 psi (normal), temp lower green (normal)

Watched the oil pressure drop to 0 psi within 3 seconds like during an engine shut-down. Engine noise normal, no new vibrations, etc.

Pull back to 2000 and point towards nearest airport 18 miles away. ~2-3 minutes later, oil pressure climbs back to normal like a normal start-up!!

Land at Natchez MS and start checking: 5.5 qrts, no new leaks, nothing visually out of place. Check the pressure relief - clean. On ground run, have no pressure. Eventually pulled engine gauge fitting and ran engine. No oil in lifter gallery.

Pick-up screen checked - clean. Had to leave plane and continue on by car.

Engine is a C-145 w/ an external AirWolf filter system since rebuild. Current filter has ~15 hours on it. They have always been clean inside.

Have several ideas. Anyone here fight something like this?

Thanks in advance
Steve Webre
N3812V
Broussard, LA.
swebre@ccaconsultants.net
swebre@hotmail.com

[cessna170bdriver]

Steve,

I had a similar problem in 2001, at 1000 hrs and 10+ years SMOH, only I caught it on the ground. I suspected the 40-something year old gauge, so my mechanic direct-connected a known good gauge, which showed zero oil pressure. He removed the relief valve, which looked clean, and reinstalled it. Next start: 30-35 psi oil pressure. I kept an eye on it, and it never occured again, but next oil change a few months later found the filter full of aluminum particles. It turned out to be a piston pin plug had self destructed. The particles were too small to get caught in the pickup screen, so at least open up your filter before flying again. In addition, drain the oil through a clean cotton t-shirt and take a real close look for metal particles. I wish I had.

I'm not sure if particles from the plug caused the relief valve to stick open, or if the lack of oil caused the plug to begin to fail, or if the two were even related at all. Engine teardown did not show evidence of oil starvation to any bearings, but there were a lot of aluminum particles embedded in all bearings. There is some minor roughness on the crankshaft, but a quick check witha mic shows a possibility of the crankshaft still being servicable. The engine is still in parts in my garage, and I'm still running a used replacement engine.

I hope you have a better outcome.

Miles

[swebre]

Thanks for the feedback Miles. Excellent points all.

Rescue mission will be underway shortly. Plan to either find the problem Saturday and fly it out or trailer it home. Ron Massicot has graciously offered his trailer and hotshot services if needed. No small offer considering the time involved....

We have dissected another C-145 that is down for an OH so have a good handle on the oil system. Everything points to something plugging the pump suction in the pan or a total failure of a Champion filter on the Airwolf system. Both are low percentage shots but little else makes sense at this point. Once we attack the plane w/ proper tools, hopefully we can solve this mystery.

Smooth air,

-Steve-

[cessna170bdriver]

Ron is a good example of what this Association is all about. I had a cracked cylinder over Dover, DE on the way to the Lancaster, PA convention in '93. Ron called home and had a neighbor FedEx his spare overhauled cylinder to PA. Then Ron and another convention goer took a day out of the convention to drive down and help me install it! Good people.

Miles

[swebre]

Just to close this chapter, this is what we found:

Well, 3812V flew home Saturday. Once we got to the plane, we started flushing and logically troubleshooting the system. Then we stumbled onto something that amazed us.

The AirWolf remote filter system was plumbed backasswards! Checking the logs and it appears that at least since the engine was rebuilt in late 1997, oil has been flowing into the CENTER of the filters and flowing up the outside.....

Just amazing the we haven't had a problem before!

Also explains why the filters alway look so clean when cut open and the outside pleats checked.

Anyway, flushed everything, caught all returns and no hint of metal anywhere. Installed an original screen system and got a good ground run before flying it home.

Life is good again.

Never take anything for granted......

-Steve-

[cessna170bdriver]

Great news Steve!

[MontanaBird]

It was interesting reading Swebre's discussion. Last month I was 8,500 enroute to Spokane, 8 miles west of Missoula. Oil pressure dropped out of the green, and varied directly with throttle setting. My pulse rate increased drastically.

50 SMOH on my C-300, stock oil screen with no filter. All previous changes clean, no particles when screen inspected. Immediately landed MSO, ingested coffee. Upon inspection, found no indication of damage, lost oil, or 'real' problem. Oil level normal ( 6-1/2 qts.).

My ace mechanic/Flight Maintenance Manager said, probably a tiny piece of something (carbon...) likely caused relief valve to get stuck open.

Upon restarting after engine cooled, oil pressure normal, and has been ever since. He said tiny piece likely flushed out when relief valve popped open again, and story over.

10,500ft over Mississippi for Swebre. I think that qualifies for space flight, doesn't it?

[cessna170bdriver]

10,500ft over Mississippi for Swebre. I think that qualifies for space flight, doesn't it?

Must be something about the air over that way. I set my personal altitude record in my 170 of 14,500 near the Louisiana - Mississippi border. 45 minutes from 23ft MSL to 14,500.

Miles

[GAHorn]

It was interesting reading Swebre's discussion. Last month I was 8,500 enroute to Spokane, 8 miles west of Missoula. Oil pressure dropped out of the green, and varied directly with throttle setting. My pulse rate increased drastically.

50 SMOH on my C-300, stock oil screen with no filter. All previous changes clean, no particles when screen inspected. Immediately landed MSO, ingested coffee. Upon inspection, found no indication of damage, lost oil, or 'real' problem. Oil level normal ( 6-1/2 qts.).

My ace mechanic/Flight Maintenance Manager said, probably a tiny piece of something (carbon...) likely caused relief valve to get stuck open.

Upon restarting after engine cooled, oil pressure normal, and has been ever since. He said tiny piece likely flushed out when relief valve popped open again, and story over.

10,500ft over Mississippi for Swebre. I think that qualifies for space flight, doesn't it?

There is no "relief valve" to get stuck open ...with the original screen system. (One of the advantages of a spin-on filter system is the inclusion of a relief valve in most popular spin on filters.)

[alaskan99669]

Then what is #19 in this drawing from the "Continental Aircraft Engine Illustrated Parts List" for the C-125, 145 and 0-300 engines?

[GAHorn]

It's a "relief valve". I was actually thinking of a bypass valve. (It's late for me.) Sorry to have confused the issue with my use of incorrect terminology. I was still thinking of Steve's reversed oil filter set-up, and the bypass valve operation in that situation.
(Of course, the illustration is not that of the C145/O300 oil pressure relief valve. It appears to be that of the C125 oil cooler assembly.)