Oil Consumption - is this normal?

[Red Leader]

I have noticed over the last couple of years that my Continental engine uses very little oil, like VERY little oil. Over my 25 hours between oil changes, I rarely have to add a full quart. Careful measurements before my last trip (flight time of about ten hours) showed my engine went through, at most, only half a quart - probably not even that much. I read another posting where a trusted contributor said that using no oil is a red flag. Because in the grand scheme of things this is nearly next to no oil use, I am concerned. As a background, my engine has about 1500 hours on it with about 300 on a new top-end and turbo.

I have asked for an oil analysis at each change but between it being forgotten by the A&P each time (and one being sent out with the results never being returned), no analysis history has been established. I am putting my plane in for an annual in a couple of weeks and will ask AGAIN for the shop to send off a sample. Is this level of consumption normal? What results should I expect with such little use? 

[ArtVandelay]

I don’t see lack of oil consumption as a red flag. If the oil isn’t getting to the cylinder walls, then yes.
I would borescope the cylinders.
I never remember needing to add oil between oil changes (12-15k miles) on any modern cars I’ve owned, so that alone isn’t a problem.

[GeeBee]

A liquid cooled automobile engine and an air cooled engine are two different things especially when it comes to  ring end gap and other tolerances.

That said, to the OP, why do you need your mechanic to get an oil sample? Buy a suction pump from Blackstone and pull the sample yourself and send it in yourself. Not hard to do. You are being badly served by your present shop.

[anthonydesmet]

I’d keep enjoying the flying and not worry.  Sounds like you’re establishing a new baseline of consumption after the overhaul.  I do 25 hour changes and on my newly (250 hours) overhauled engine I also add a little over a quart between changes. Before overhaul I was also about 1.5 to 2 quarts every 20.  I assume the oil is showing wear (getting dirty) around 10 hours.

as mentioned above you can pull your own oil.  Both Blackstone and AVLAB come with suction cup or a tube you can pull. Do it right before annual/oil change.

oil analysts, oil consumption, compression, operating temps, routine borescope all establish a baseline.  Small changes from baseline normally = use/age....that we try and prolong with smart operations/temperature control, frequent oil changes, etc……..large changes in a short time = something more serious is happening or about to happen/failure.

[Pinecone]

There was an issue in the 90s or early 2000s with new Continental cylinders using NO oil.  Even with longer oil change intervals.  And such cylinders only lasted a few hundred hours.

If you are burning SOME measurable amount, I would not worry.  But I would start taking your own samples and sending them in

[Red Leader]

The shop that would forget or said they sent it in (and likely didn't) is no longer doing my annuals. My new shop did not take a sample last time because I asked for an analysis after they had already drained the oil (my bad). Whenever my oil change is due, it still looks like new. I guess that is good, but my last engine (on a different plane with much fewer hours) burned about a quart every 9-10 hours like clockwork. My Cessna, previous to that one, had a mid-to-high time engine and burned a quart every 7 hours. I am just surprised that this high-performance, turbo-charged Continental engine uses such little oil. Of course, I am careful how I run it, but thanks for easing my concerns!

[Danb]

Not using much oil wouldn’t bother me but it looking like new when you do your oil change, I wonder if it’s doing the job. I’ve never seem oil look like new during an oil change,25+ hours. I’d consider doing a borescope and take a look.D 

[A64Pilot]

I had a factory reman IO-520 about 2005. It would honestly burn 1 gt in 50 hours, and I ran it ROP at best power and never backed off full throttle until time to land, ran it about 1000 hours with 0 problems, not even a fouled plug, then I Retired from the company.

Only engine I have ever seen that burnt so little oil, it didn’t even leak a drop either.

It was the Company’s airplane and they bought the fuel, and time is money.

[A64Pilot]

2 hours ago, Danb said:

Not using much oil wouldn’t bother me but it looking like new when you do your oil change, I wonder if it’s doing the job. I’ve never seem oil look like new during an oil change,25+ hours. I’d consider doing a borescope and take a look.D 

Oil turns color as a function of blow by, lots of blow by it turns black in an hour or two, very little color = very little blow by. Lack of blow by is desirable, but sort of uncommon as our engines being air cooled have loose tolerances, they have to as cylinder temp variation and therefore expansion is so great. Run one at water cooled engine tolerance's and it will seize. So why low blow by is the goal, it’s not often achieved.

Oil does not turn color as a function of wear or breaking down etc, it’s carbon from blow by. Diesels turn oil black fast from the soot from the Diesel fuel burning.

Ever drained the oil on an engine that runs on Propane? It looks just like it came out of the bottle, no carbon from propane so the oil stays looking new.

When I sample I do so at oil change just get it as it’s about half drained. Military we sampled at time intervals but didn’t change oil, then we used a dip tube, like a soda straw just bigger.

Personally I’d be very happy about it, low blow by is good, less acid build up in the oil, less carbon is good because carbon is abrasive etc.

There was a study done a very long time ago that tied cylinder wear to oil consumption, meaning one that used oil had lower wear, assumption is of course the oil being used lubricated the compression rings on its way to being burnt.

But if there is wear, oil consumption will soon follow, not excessive, but probably “normal” but in all honestly there doesn’t seem to be a normal oil consumption, average of course, but low time engine with good compression that make good power etc have oil consumptions all over the place and it just doesn’t seem to make much difference, they last just as long etc.

But having cleaner oil for longer can’t be anything but good.

[Red Leader]

That was an excellent explanation - thank you! My last oil change (many months ago) was new-looking enough the the A&P called me to say so. Guess that is good, right?

[A64Pilot]

15 hours ago, Red Leader said:

That was an excellent explanation - thank you! My last oil change (many months ago) was new-looking enough the the A&P called me to say so. Guess that is good, right?

I think it is, but even if it’s not, what are you to do about it?

A theory and there is likely some merit to it is that if you use almost no oil then your cylinders won’t last. 

Only cure for that that I can see is to replace them, but wouldn’t it make more sense to run what you have until replacement is required?

In my one case instance that wasn’t the case because at 1000 hours they all had great compressions, but that’s one case too, and I worked to keep temps down.

My personal belief is that cyl head temp is tied more to longevity than most any other metric, do not be afraid to open the cowl flaps, that’s why they are there. Many because they were taught that way close them immediately at the top of the climb, and will cruise at higher than desired head temps.

I don’t have an engine analyzer so I can’t give you actual temps, but there is no MP/RPM with my NA engine that I can’t maintain middle of the green head temps, now on a hot day that means climbing at only 500 FPM and 130 KIAS, but it can be done.

Remember most everything you get, even from an “expert” is an opinion, none warranty their advice, so always operate the engine IAW the POH / engine manual

[Red Leader]

Yes, I fly carefully, climb more slowly than what my plane is capable of and care for my engine temps with vigilance. My last annual, compressions were all 76-78/80 - I was most pleased. My 25 hour oil changes are, from what I understand, an accepted practice for a turbo-charged engine. Not always have I waited to reach the 25 hour mark to change the oil so that also helps. From what I am able to glean here is that things are good if my oil usage is down, compressions are high, engine maintenance is performed regularly, and engine management is monitored carefully during flight. My new Insight G5 assists me with monitoring all aspects of engine performance - so far, so good.

[Utah20Gflyer]

If the bore scope looks good I would continue on as you have been doing.  I’d start doing oil analysis as another data point.   

[Red Leader]

My mechanic called last Friday with an update, and I asked about the borescope results and was happily informed that the cylinders look great - no corrosion, no scoring, the valves have good pizzas, great compression and even the crosshatching is still visible! With the information provided above by the knowledgeable members of MooneySpace, and the update from my mechanic, I no longer have any concerns about my engine. Thanks guys!

[glenn reynolds]

I suggest that you purchase a six pack of oil sample kits Prepaid - from blackstone lab.  the kits will be in your name with your n number on the paperwork.  I simply put the kit on the pilot seat on top of the plane key in the airplane when I drop it off.  The kits come with a prepaid mailer and since you purchased them, blackstone already has your email address to send the report to.  there are several oil analysis companies and it's hard for mechanics to stock sample kits from each of the vendors and then fill out the paperwork and get it to the post office etc.  I keep both filters and oil and sample kits in my hanger, I fly for work and so having made calls to confirm availability, I often have oil changes done while I'm on the road.