Oil Analysis - Help

[MooneyP87]

My partner and I are closing a deal on a 68' C Model. The airplane sat in an enclosed hangar for 3 years up until this past year when Air Mods purchased it from a widow. I believe air mods has put around 20 hours or so on the engine since their purchase. We just received the oil analysis back (attached). It appears the aluminum, chromium, and iron have double the PPM than the average. Granted this is comparing a 12 hour oil interval against 30 hour averages. Do you guys think this is just corrosion/oxidation build up since the airplane sat or is there a higher chance this could be a much larger issue. The engine does have 1,478 hours on it so we are prepared to do a top OH in the next year or two.

[nfonville]

I saw the exact same thing with my Bravo 1850+ hours when I purchased in January.  Those same exact values were a bit high on the first oil change.  The previous owner only used the plane 10 or so hours per year but was hangered.  The numbers got better with each oil change at 25 hours of flying time. I put 120 hours on her since January and the analysis looks really good now. Fly the plane to 25 hours and repeat.  Not sure if yours has a filter but make sure to cut it open and inspect if it does.  Mine was very clean with very little in it.

[MooneyP87]

There was no indication on the oil filter of an issue when it was cut during the prebuy oil change.

[carusoam]

Normalize the data so the hours match using a proper multiplier...

OK to assume a linear relationship.

Expect funky data just from sitting...

What you really want to know is if the cam and followers are showing corrosion issues...

What are cams and followers made of?

Tough to price/buy a plane that hasn’t moved in years...

inspecting only parts of the IO360 cam requires removing a cylinder...

PP thoughts only, not a mechanic...

Best regards,

-a-

[Oldguy]

Fly it on a regular basis (twice a week would be good) and do another oil change at 25 hours or so. Watch the color of the oil as well as the usage. If you see it getting dark quickly you may have some blow-by. You didn't say what oil you are using and if you added anything like Camguard. Multiple opinions on oil and additives, but decide on what you want to run and stick with it for a while to get consistent analyses across oil changes.

Our engines like being flown regularly. Mine had 50 hrs. over 2 years when I bought it, but it over the past 5 years it has had about 500 put on it. Still running well at ~1600 hrs. and oil analysis is stable.

[MooneyP87]

Thanks guys, I am not sure what oil the previous owner was using at the moment. The pre-buy shop recommended we run marvel mystery oil in the fuel for a while to try and help remove any corrosion. I would think that since we don't have any visible metal in the oil filter that there isn't a huge issue at the moment.

[exM20K]

If you’re concerned about corrosion, consider borescoping the cylinders and spending the labor to pull a cylinder to get eyes on the bottom end.  Oil analysis is great but uncertain, and I’d want certainty that I’m not making the seller’s problem mine.

[Oldguy]

14 minutes ago, MooneyP87 said:

Thanks guys, I am not sure what oil the previous owner was using at the moment. The pre-buy shop recommended we run marvel mystery oil in the fuel for a while to try and help remove any corrosion. I would think that since we don't have any visible metal in the oil filter that there isn't a huge issue at the moment.

Can @M20Doc or some of our other A/Ps comment on this?

[Andy95W]

At the end of the day, it's still- and always- a crap shoot.  The oil analysis will probably get normal after a few oil changes.  But whether or not it makes it to 2,000 hours is an unknown until you hit 2,000.

I've seen engines overhauled in the 1980's and barely flown for a decade get to TBO.  Just recently, at my airport, I've seen a Piper Arrow in the flight school, flown regularly, need a new camshaft after 500 hours.  And yes, they were using Camguard.

I'd make sure I had a spare $10k available for potential engine work and take my chances.  If you don't need to use it, you can put it toward the overhaul eventually.

[MooneyP87]

8 minutes ago, Andy95W said:

At the end of the day, it's still- and always- a crap shoot.  The oil analysis will probably get normal after a few oil changes.  But whether or not it makes it to 2,000 hours is an unknown until you hit 2,000.

I've seen engines overhauled in the 1980's and barely flown for a decade get to TBO.  Just recently, at my airport, I've seen a Piper Arrow in the flight school, flown regularly, need a new camshaft after 500 hours.  And yes, they were using Camguard.

I'd make sure I had a spare $10k available for potential engine work and take my chances.  If you don't need to use it, you can put it toward the overhaul eventually.

Agreed, we're putting enough back to at least do a top overhaul in a shared kitty. We are going to go through with it and hopefully these will come down to average PPM. Thank you guys for the input.

[DXB]

Though you can't tell much from one data point, it's exactly what you'd expect from an engine that sat that's now being flown. Maybe you'll get lucky and the engine will be fine. More likely than not you'll need cylinder work in the near future. Maybe you'll end up with spalled tappets and cam lobes and need an overhaul soon, but after a few hundred hours you'll feel more confidence that this worst outcome is not imminent.   

It's a crap shoot with an engine that sat, no matter what the oil analysis says right now.  There's no way to guide your buy decision here based on the oil analysis.  Personally I wouldn't bother with it - pointless stress  with almost no actionable information from looking at the numbers.  If you buy it, track oil consumption, learn to borescope the valves, look for metal in the filter at every oil change, learn to use the engine monitor. 

[INA201]

Mine was very similar. Sat for a couple of years and had high numbers.  I did it differently than most and changed the oil every 15 hours a couple of times after bringing her home.  I didn’t want extra iron and old carbon floating around.  What I did notice is that I had a lot of carbon show up in the filter.  I run lean of peak and think that a lot of stuff got cleaned out during those first couple of oil changes.  After that I went to a 25 hour schedule and started analyzing the oil data. Three years later and the numbers are are still normal.  I took the crapshoot and feel pretty confident now, knock on wood.  If you get an appropriately discounted purchase price and like the plane then it can be worth the risk imop.

[MooneyP87]

We're going to install an engine monitor in a month or two so we can better track any issues before they occur. Picking it up this Saturday from Air Mods. They are top notch people, Brian has been great for us to work with and has went above and beyond to fix items on it that we didn't even request him to correct. We're going to take the risk and check the oil and filter every 25 hours. Hopefully we will be able to burn most of build ups out and have a great engine for a few more years. If not, we will be prepared to over haul it.

[INA201]

Sounds like a plan.  Please let us know how it goes.  Hopefully you’ll have no issues.