How big of a hit is my wallet about to take?

[406Propjunkie]

I purchased a Cessna 150 with an o-200 late last year, the engine has 700ish hours since factory new from Continental but it has sat for quite a while.

We went ahead and replaced the accessory housing, oil pump gears, cover and oil pressure relief valve as it was having a hard time staying primed.

It’s flown probably 25 hours since I got it, runs like a top, all the cylinders are in the upper 70s and overall it’s been very reliable for me.

A few weeks ago on an 85 degree day I was doing touch and goes and on the 4th lap around the pattern I saw oil pressure indications that I didn’t like.

It was leaned for max rpm, and we were climbing out at VX to stay close to the airport.

At idle it would sit right below the red line, in flight at 1400rpm it would sit right above the red, and in cruise with full throttle it would sit just below the green.

I know in these small continentals, oil pressure issues are kind of a common thing.

I keep reading mixed opinions as to what to expect. Continental manual says 10psi min @ idle, 30psi in cruise. Every gray haired A&P I’ve talked to says “it’ll run past TBO don’t worry about it”

I’ve attached photos of the indications we were getting. I’m not thrilled about them.

 

[RyanShort1]

It’ll cost you everything if you don’t address it correctly and don’t have the flying skills and judgment to deal with the failure mode.

 

[Doc Holliday]

Have you asked a mechanic to trouble shoot this? Has the gauge been checked for accuracy?

 

[Darryl Snover]

First thing I'd do is verify that the sender (if electrical) and gauge are good, and reading accurately. From there, oil pressure problems can be a bunch of things. Is the engine all of a sudden making metal? What's in the oil filter/screen? Any bearing material?

 

[Domenick]

...We went ahead and replaced the accessory housing, oil pump gears, cover and oil pressure relief valve as it was having a hard time staying primed. ...

I am not familiar with the Conti O-200, but I ask this:

Is the "new" oil pressure relief valve set incorrectly or malfunctioning?
Always suspect the last changes.

These *may* help: https://www.pilotsofamerica.com/community/threads/o-200-oil-pressure.135334/

O-200 Loses Oil Prime

edited

www.pilotsofamerica.com

 

[GeorgeC]

A few weeks ago on an 85 degree day I was doing touch and goes and on the 4th lap around the pattern I saw oil pressure indications that I didn’t like.

It was leaned for max rpm, and we were climbing out at VX to stay close to the airport.

I assume you're not at sea level?

 

[Dan Thomas]

If the pressure is reading high, it's usually a sticking relief valve. Might be a bit of crud or metal stuck in it. It's a simple spring-loaded plunger that closes off a port in the oil pressure gallery, and when the pressure rises to the set limit, it opens and bleeds some of the oil off back into the case. The new accessory housing and pump gears enable the high pressure, since those little Continental oil pumps are rather marginal to begin with compared to a Lycoming's.

Losing prime is a different problem. The oil pump is part of the accessory case, and the gears are in machined cavities in that case, and covered by a thick aluminum plate that is lapped to be very flat. The clearances between the gears and cover and machined cavity are tiny so that the pump can actually move any air out of it so as to suck oil up from the sump, which is well below the pump. That cover gets worn and scored and warped by trash in the oil, as the filter is downstream of the pump, and any metal or bits of carbon that come up with the oil go through that pumps and chew up the aluminum. That wrecks the suction capabilities of the pump when it comes to getting the air out and oil in. Once the oil is in there, it works OK. The cover plate warps, like I said, especially if the rebuilders don't lap it flat, or if they overtighten the hardware, and after shutdown the oil in the pump slowly leaks out, leaving air in there that the pump can't move due to the scoring and wear. There is not enough surface area for sealants to work between the plate and case, either, and anything you put in there will just get blown out by the pressure.

Really common problem with old small Continentals. There are no new accessory cases for the A-65 thru C-90, either, and no approved means of fixing the scored pump bore. Some owners have to remove the oil temperature bulb from the screen housing and pump oil into that hole; it runs down into the pump to prime it, and the pressure will then come up after startup. If you don't do this, the engine will run without oil pressure until you shut it down, and the crank and rod bearing surfaces get badly worn. Been there, done that. Had the crank ground, replaced the bearing shells, and made a manual preoiler for my homebuilt Jodel. Just a big primer. It took oil from the oil tank and pumped it into the oil pressure port via a check valve and tee. 15 or 20 pumps before startup filled the pump and all the galleries and bearings and stuff and the pressure is instant on startup. One can do that with a homebuilt, and no, I do not make these things to sell. No STC for it anyway. It mounted to the engine mount near the aft left side of the engine.

 

[406Propjunkie]

Have you asked a mechanic to trouble shoot this? Has the gauge been checked for accuracy?

All troubleshooting has been done with a mechanic supervising as I log the time for my A&P.

Currently waiting for a gauge to show up.

 

[406Propjunkie]

First thing I'd do is verify that the sender (if electrical) and gauge are good, and reading accurately. From there, oil pressure problems can be a bunch of things. Is the engine all of a sudden making metal? What's in the oil filter/screen? Any bearing material?

We changed the oil 5hrs after the accessory case replacement as it doesn’t have a filter.

The screen had a very small amount of metallic material in it, but none was magnetic and the oil has been clean since.

 

[406Propjunkie]

If the pressure is reading high, it's usually a sticking relief valve. Might be a bit of crud or metal stuck in it. It's a simple spring-loaded plunger that closes off a port in the oil pressure gallery, and when the pressure rises to the set limit, it opens and bleeds some of the oil off back into the case. The new accessory housing and pump gears enable the high pressure, since those little Continental oil pumps are rather marginal to begin with compared to a Lycoming's.

Losing prime is a different problem. The oil pump is part of the accessory case, and the gears are in machined cavities in that case, and covered by a thick aluminum plate that is lapped to be very flat. The clearances between the gears and cover and machined cavity are tiny so that the pump can actually move any air out of it so as to suck oil up from the sump, which is well below the pump. That cover gets worn and scored and warped by trash in the oil, as the filter is downstream of the pump, and any metal or bits of carbon that come up with the oil go through that pumps and chew up the aluminum. That wrecks the suction capabilities of the pump when it comes to getting the air out and oil in. Once the oil is in there, it works OK. The cover plate warps, like I said, especially if the rebuilders don't lap it flat, or if they overtighten the hardware, and after shutdown the oil in the pump slowly leaks out, leaving air in there that the pump can't move due to the scoring and wear. There is not enough surface area for sealants to work between the plate and case, either, and anything you put in there will just get blown out by the pressure.

Really common problem with old small Continentals. There are no new accessory cases for the A-65 thru C-90, either, and no approved means of fixing the scored pump bore. Some owners have to remove the oil temperature bulb from the screen housing and pump oil into that hole; it runs down into the pump to prime it, and the pressure will then come up after startup. If you don't do this, the engine will run without oil pressure until you shut it down, and the crank and rod bearing surfaces get badly worn. Been there, done that. Had the crank ground, replaced the bearing shells, and made a manual preoiler for my homebuilt Jodel. Just a big primer. It took oil from the oil tank and pumped it into the oil pressure port via a check valve and tee. 15 or 20 pumps before startup filled the pump and all the galleries and bearings and stuff and the pressure is instant on startup. One can do that with a homebuilt, and no, I do not make these things to sell. No STC for it anyway. It mounted to the engine mount near the aft left side of the engine.

View attachment 128640
View attachment 128641

Yes. The loss of prime is why we went as far as we did.

The previous owner had this issue, and I wanted to fix it before I flew it at all.

It hasn’t lost prime since.

 

[Dan Thomas]

Re the oil pressure indication: I don't think any 150s had electric oil pressure gauges. All mechanical, IIRC. But that doesn't mean that the gauge itself is tired and failing. And then, too, that gauge might have been replaced with an electrical conversion kit; see below.

Electric oil temp and pressure indications can be thoroughly screwed up by bad engine grounding. The alternator is umping electrons from the positive bus, through the alternator, and into ground. If the alternator's ground cable to the firewall is old and corroded and oily and loose, or if there is maybe no ground cable at all, the electron flow is into the engine crankcase and then to the airframe via a ground cable or strap to the engine mount or firewall. More places for bad connections. So a tiny resistance here tends to coax the electron flow into finding other paths, and via the temp or pressure senders is one of them. The electron flow is normally from the sender to the gauge, so any extra flow will make the gauge read high. The electrons push their way into the sender, through the wire to the gauge, and from the gauge to the bus via a fuse or breaker.

Cessna offered an electrical conversion kit for the oil temperature gauges in their older airplanes. The original system used a metal bulb that was secured in the oil screen housing, with a tiny tube to the gauge, which was really a pressure gauge, calibrated in degrees. The bulb, line and gauge were all oil-filled and sealed, and when the bulb warmed up in the engine oil, the oil in the bulb expanded and created pressure that drove the gauge up. Removing that bulb every time the screen was cleaned eventually broke the tiny metal tube and the oil leaked out and the gauge was dead. Expensive to fix. The electrical conversion was much better. But they had issues with gauge fluctuations and overreading, and it was because of bad grounds between the engine and airframe. So the fix was a small wire from the case near the sender to the gauge's case to neutralize any voltage differential.

If you have hard cranking during start, it's often because the engine grounding is poor. A tiny resistance where large current is involved means a large voltage drop, and the starter doesn't get what it should.

 

[406Propjunkie]

Re the oil pressure indication: I don't think any 150s had electric oil pressure gauges. All mechanical, IIRC. But that doesn't mean that the gauge itself is tired and failing. And then, too, that gauge might have been replaced with an electrical conversion kit; see below.

Electric oil temp and pressure indications can be thoroughly screwed up by bad engine grounding. The alternator is umping electrons from the positive bus, through the alternator, and into ground. If the alternator's ground cable to the firewall is old and corroded and oily and loose, or if there is maybe no ground cable at all, the electron flow is into the engine crankcase and then to the airframe via a ground cable or strap to the engine mount or firewall. More places for bad connections. So a tiny resistance here tends to coax the electron flow into finding other paths, and via the temp or pressure senders is one of them. The electron flow is normally from the sender to the gauge, so any extra flow will make the gauge read high. The electrons push their way into the sender, through the wire to the gauge, and from the gauge to the bus via a fuse or breaker.

Cessna offered an electrical conversion kit for the oil temperature gauges in their older airplanes. The original system used a metal bulb that was secured in the oil screen housing, with a tiny tube to the gauge, which was really a pressure gauge, calibrated in degrees. The bulb, line and gauge were all oil-filled and sealed, and when the bulb warmed up in the engine oil, the oil in the bulb expanded and created pressure that drove the gauge up. Removing that bulb every time the screen was cleaned eventually broke the tiny metal tube and the oil leaked out and the gauge was dead. Expensive to fix. The electrical conversion was much better. But they had issues with gauge fluctuations and overreading, and it was because of bad grounds between the engine and airframe. So the fix was a small wire from the case near the sender to the gauge's case to neutralize any voltage differential.

If you have hard cranking during start, it's often because the engine grounding is poor. A tiny resistance where large current is involved means a large voltage drop, and the starter doesn't get what it should.

Thanks for the very in depth and concise response!

My airplane still has the old mechanical bulb style temp gauge as well as the original pressure gauge.

 

[406Propjunkie]

It’ll cost you everything if you don’t address it correctly and don’t have the flying skills and judgment to deal with the failure mode.

That’s a fact!

 

[406Propjunkie]

I assume you're not at sea level?

Field elevation is 3550

 

[Mikey52]

What oil are you running?

If it's still a mechanical oil pressure gauge, it's possible for air to get in that line and then you'll read lower than actual pressure.

Have the cylinders been off. At 700 hours there is a good chance you may have a piston pin stuck. That will cause non magnetic material to show up in the screen. If you had a filter you would find many more smaller pieces in the filter. These pins have an aluminum cap on each end that allows the pin to ride on the cylinder walls without wearing the walls. When a pin becomes stuck it will wear the aluminum off then score the cylinder walls. This could be the beginning of a stuck pin. Without a filter the smaller pieces could get stuck in the crank bearing oil passages, or into the bearings its self, scoring the bearings and causing a decrease in oil pressure due to leakage back to case. The oil pressure port is the last place for oil to be measured before it dumps back to sump.

Suggestions.

Have cylinders borescoped next time you check compression. Or clean plugs.

Install a filter. This will double the oil change interval. And catch more contaminants. It's also easier to collect the things you do find.

Do oil analysis, I like blackstone because of the notes and analysis a real human does. We were warned about the piston pin problem before we had a cylinder wear too much for service.

Don't shim the oil relief valve. That will just mask the real problem.

http://www.bowersflybaby.com/tech/fenton.html

 

[406Propjunkie]

What oil are you running?

If it's still a mechanical oil pressure gauge, it's possible for air to get in that line and then you'll read lower than actual pressure.

Have the cylinders been off. At 700 hours there is a good chance you may have a piston pin stuck. That will cause non magnetic material to show up in the screen. If you had a filter you would find many more smaller pieces in the filter. These pins have an aluminum cap on each end that allows the pin to ride on the cylinder walls without wearing the walls. When a pin becomes stuck it will wear the aluminum off then score the cylinder walls. This could be the beginning of a stuck pin. Without a filter the smaller pieces could get stuck in the crank bearing oil passages, or into the bearings its self, scoring the bearings and causing a decrease in oil pressure due to leakage back to case. The oil pressure port is the last place for oil to be measured before it dumps back to sump.

Suggestions.

Have cylinders borescoped next time you check compression. Or clean plugs.

Install a filter. This will double the oil change interval. And catch more contaminants. It's also easier to collect the things you do find.

Do oil analysis, I like blackstone because of the notes and analysis a real human does. We were warned about the piston pin problem before we had a cylinder wear too much for service.

Don't shim the oil relief valve. That will just mask the real problem.

http://www.bowersflybaby.com/tech/fenton.html

We are running Phillips XC 20w50.

I have a case of straight 100w on its way as I’ve seen some say it makes a noticeable difference.

I’m a bit skeptical as SAE50 is SAE50 regardless of whether it is a multi grade or not. But we’ll give it a shot.

I like the idea of running an oil filter on it, however I can’t help but wonder what folks did back when these engines were new. Surely they had the same problems, I guess back then it was probably less than the down payment on a house to just have an overhaul done.

We have borescoped it, found nothing out of the ordinary.

That link you included (I found it a few months ago) has been a ton of help in understanding the shortcomings of these engines, I fear that splitting the cases is in my future. But I’d like to exhaust every other option before it gets to that.

 

[Mikey52]

Was the previous owner running the phillips oil. I have heard but no first hand knowledge that changing oil types might be a no no. Ours does run right on the red line at idle when hot. If you live in a colder climate the 20x50 might be better because it will flow better at colder temps. At 200 degrees oil temp, the straight 50 and 20x50 will have the same viscosity.

On the borescope all you might see is a little hue change on the sides of the cylinder facing front or facing back in the early stages.

 

[RyanB]

I have heard but no first hand knowledge that changing oil types might be a no no.

I don’t know where that load of baloney came from, but it’s far from true. The engine doesn’t have the ability to differentiate between Phillips and Aeroshell.

 

[Mikey52]

I don’t know where that load of baloney came from, but it’s far from true. The engine doesn’t have the ability to differentiate between Phillips and Aeroshell.

In principal I agree. But it wasn't originally built for a multi grade oil. And I believe the TCDS calls for 80 grade or 40 weight oil.

 

[406Propjunkie]

Was the previous owner running the phillips oil. I have heard but no first hand knowledge that changing oil types might be a no no. Ours does run right on the red line at idle when hot. If you live in a colder climate the 20x50 might be better because it will flow better at colder temps. At 200 degrees oil temp, the straight 50 and 20x50 will have the same viscosity.

On the borescope all you might see is a little hue change on the sides of the cylinder facing front or facing back in the early stages

Was the previous owner running the phillips oil. I have heard but no first hand knowledge that changing oil types might be a no no. Ours does run right on the red line at idle when hot. If you live in a colder climate the 20x50 might be better because it will flow better at colder temps. At 200 degrees oil temp, the straight 50 and 20x50 will have the same viscosity.

On the borescope all you might see is a little hue change on the sides of the cylinder facing front or facing back in the early stages.

where in the green does your needle typically stay at 2400rpm?

 

[Dan Thomas]

If it's still a mechanical oil pressure gauge, it's possible for air to get in that line and then you'll read lower than actual pressure.

Baloney. That idea violates the gas laws. When there is no movement in the system, the pressures are equal throughout the system whether it's oil or air. Some people will deliberately introduce some air into the line to damp pulsations from the pump; this is commonly done with mechanical engine-driven fuel pumps. The only reason to have all oil in the oil pressure line is to get a quicker pressure reading after startup, but in cold weather that oil gets too viscous and slows the reading tremendously. We used to put 5606 hydraulic fluid in that line to eliminate that delay.

In principal I agree. But it wasn't originally built for a multi grade oil. And I believe the TCDS calls for 80 grade or 40 weight oil.

From the TCDS:



SAE 20 is Aviation 40. SAE 40 is Aviation 80. Aviation 100 is SAE 50.

From Continental's M-O Standard Practices Manual:




https://pceonline.com/wp-content/uploads/2017/04/M-0standardpractice2017-01-15.pdf

 

[RyanB]

In principal I agree. But it wasn't originally built for a multi grade oil. And I believe the TCDS calls for 80 grade or 40 weight oil.

Sure, but they also didn’t have multi weight oils in the 40’s when that TCDS was written. As technology has improved, so has the literature from manufacturers on acceptable operating standards.

 

[Steamflyer]

Before you replaced the accessory case and oil pump, what was the oil pressure in the engine (the one that was hard to keep primed, but presumably you ran it at least once).

Those appear to be some fairly low oil pressure readings. FWIW I have run Phillips X/C 20W-50 in a C-85 (very similar to an O-200) with no issues hot or cold. Also in every other airplane I've had, save for break-in when I follow the overhaul manual recommendations.

 

[406Propjunkie]

Before you replaced the accessory case and oil pump, what was the oil pressure in the engine (the one that was hard to keep primed, but presumably you ran it at least once).

Those appear to be some fairly low oil pressure readings. FWIW I have run Phillips X/C 20W-50 in a C-85 (very similar to an O-200) with no issues hot or cold. Also in every other airplane I've had, save for break-in when I follow the overhaul manual recommendations.

I’ve never ran the engine with the old accessory case in it, the previous owner mentioned the priming issue when I went to buy it, I was unable to get it to prime just cranking with the mixture pulled out so we started investigating before we caused any additional damage.

 

[Mikey52]

You asked me earlier, but I had to ask my son, because I haven't flown it in a year or two. He said the oil pressure would run about halfway between the bottom of the green and the white line. That was at cruise power in Florida.

It would be a half a needle below the min line after a couple hours flight at idle.

Engine times 9523 since new and 2458 since last overhaul.

 

[Steamflyer]

I’d tee in an external gage and see what it reads (on the ground) as a start.

 

[luvflyin]

I purchased a Cessna 150 with an o-200 late last year, the engine has 700ish hours since factory new from Continental but it has sat for quite a while.

We went ahead and replaced the accessory housing, oil pump gears, cover and oil pressure relief valve as it was having a hard time staying primed.

It’s flown probably 25 hours since I got it, runs like a top, all the cylinders are in the upper 70s and overall it’s been very reliable for me.

A few weeks ago on an 85 degree day I was doing touch and goes and on the 4th lap around the pattern I saw oil pressure indications that I didn’t like.

It was leaned for max rpm, and we were climbing out at VX to stay close to the airport.

At idle it would sit right below the red line, in flight at 1400rpm it would sit right above the red, and in cruise with full throttle it would sit just below the green.

I know in these small continentals, oil pressure issues are kind of a common thing.

I keep reading mixed opinions as to what to expect. Continental manual says 10psi min @ idle, 30psi in cruise. Every gray haired A&P I’ve talked to says “it’ll run past TBO don’t worry about it”

I’ve attached photos of the indications we were getting. I’m not thrilled about them.

You won’t need a wallet anymore because there won’t be anything left to put in it anymore. Ok, punchline done, now back to those who know something about this.

 

[Dan Thomas]

Those appear to be some fairly low oil pressure readings. FWIW I have run Phillips X/C 20W-50 in a C-85 (very similar to an O-200) with no issues hot or cold. Also in every other airplane I've had, save for break-in when I follow the overhaul manual recommendations.

From the TCDS:



They do look low, especially the one in cruise. I'd still suspect a sticking relief valve. One other possibility is a blown-out accessory case gasket at the oil gallery, either the inlet side or outlet to the relief valve. The pump, in the accessory case pushes oil through a gallery in that case and through a hole in the case flange, mating gasket, and into the gallery in the crankcase. The other side has the same setup to take the oil to the relief valve. There's a small, narrow section of gasket at both places that could be broken out under pressure, and the oil would escape to the sump. Very, very rare. If the gasket broke outward, there'd be oil everywhere and a soon-seized engine.

 

[406Propjunkie]

From the TCDS:

View attachment 128665

They do look low, especially the one in cruise. I'd still suspect a sticking relief valve. One other possibility is a blown-out accessory case gasket at the oil gallery, either the inlet side or outlet to the relief valve. The pump, in the accessory case pushes oil through a gallery in that case and through a hole in the case flange, mating gasket, and into the gallery in the crankcase. The other side has the same setup to take the oil to the relief valve. There's a small, narrow section of gasket at both places that could be broken out under pressure, and the oil would escape to the sump. Very, very rare. If the gasket broke outward, there'd be oil everywhere and a soon-seized engine.

This would only manifest itself in an external oil leak as well as the pressure readings correct?

Other than that I’d need to pull the kidney and closely inspect where the case meets the crankcase right?

 

[406Propjunkie]

From the TCDS:

View attachment 128665

They do look low, especially the one in cruise. I'd still suspect a sticking relief valve. One other possibility is a blown-out accessory case gasket at the oil gallery, either the inlet side or outlet to the relief valve. The pump, in the accessory case pushes oil through a gallery in that case and through a hole in the case flange, mating gasket, and into the gallery in the crankcase. The other side has the same setup to take the oil to the relief valve. There's a small, narrow section of gasket at both places that could be broken out under pressure, and the oil would escape to the sump. Very, very rare. If the gasket broke outward, there'd be oil everywhere and a soon-seized engine.

One other thing I failed to mention, we manually blocked the oil pressure relief valve and cranked the engine with the mixture out to verify that the pump was building adequate pressure. It almost immediately made 60psi so we know for a fact that the pump makes plenty of pressure.

 

[Mikey52]

Do you still have a vacuum pump? If you do never mind, but if it's been removed I believe a plate has to be installed or you will have a loss of pressure.

 

[406Propjunkie]

Do you still have a vacuum pump? If you do never mind, but if it's been removed I believe a plate has to be installed or you will have a loss of pressure.

Do you happen to have any pictures of what this installation looks like?

 

[Mikey52]

Can't find it right now. But do you have any vacuum driven instruments left in the plane or have you gone all electric?

 

[406Propjunkie]

Can't find it right now. But do you have any vacuum driven instruments left in the plane or have you gone all electric?

It has a DG and AI that are both vacuum driven, however I don’t recall ever seeing a vacuum pump on the engine.

 

[Mikey52]

It's there, then, on front of engine, pilots side, below propeller hub.

https://www.rapcoinc.com/images/vacuum%20pumps/RAP215CC-9.gif

Have you seen this?

Oil Flow 101 for Cessna 150 and O

 

[406Propjunkie]

It's there, then, on front of engine, pilots side, below propeller hub.

https://www.rapcoinc.com/images/vacuum%20pumps/RAP215CC-9.gif

Have you seen this?

Oil Flow 101 for Cessna 150 and O

It definitely has the vacuum pump, I haven’t seen that before but I’ll have to do some reading!

 

[iflyvfr]

Aahh good old Chuck Hanna. A C150 club legend.

 

[Dan Thomas]

This would only manifest itself in an external oil leak as well as the pressure readings correct?

No. If the inside of the gasket failed it would drain into the case. No external leakage.

Other than that I’d need to pull the kidney and closely inspect where the case meets the crankcase right?

The only thing to check in there would be the oil pickup tube. If it's not lockwired it could work loose and be sucking air. The tank-to-case interface is nothing special, just a gasket.

 

[406Propjunkie]

No. If the inside of the gasket failed it would drain into the case. No external leakage.

The only thing to check in there would be the oil pickup tube. If it's not lockwired it could work loose and be sucking air. The tank-to-case interface is nothing special, just a gasket.

Very interesting stuff!

I appreciate all the information!

 

[406Propjunkie]

Just an update, we removed and inspected the oil pressure releif valve plunger.

It looked a bit uneven at the mating surface where it rides on the accessory housing.

We took a new one, lapped it to the case so the surfaces match eachother.

Test flew it for an hour with a slightly richer mixture and it did great.

I’ll be keeping an eye on it, but for now I think we may be okay.