Engine Oil Mysteriously Increased

[OntheNumbers]

This will sound like a weird question, but can the engine oil suddenly increase by 1/2 quart? I’ve been checking oil consumption before every flight and it was down to 5.1 qt and I was going to top it up after that flight. The next time I went flying the oil was suddenly at 5.6 quarts or so.

I own the plane, the engine is an O-360 and I would be the only person adding oil and ... well, I didn’t. I am not the only one with access to the hangar, but before I go asking people, I wanted to learn if there’s a way for oil to hide I an engine nd suddenly appear, Like I said, it’s a weird question.

Engine is also equipped with a spin-on oil filter and an oil cooler.

[photofly]

it depends on how long after the previous flight you check it. Shortly after a flight the oil is still distributed around the engine; after a couple of hours another half a quart or so will have drained back into the sump.

[ahramin]

Also depends on how long the dip stick has been sitting in the oil. Unless you wipe it off and reinsert it, the oil will slowly climb up the dip stick. It shouldn't make a big difference on the round one on your 360 but the flat ones can easily overread by a 1/2 quart.

But to answer your question, no the oil quantity cannot increase. The amount in the sump increases as the oil drips back down into it. The amount indicated on the dip stick can vary if it's not checked properly. The amount of oil will not increase unless something is leaking into it or was added to it. On liquid cooled engines it's usually coolant. Aircraft with oil/fuel heat exchangers it's usually fuel. On a simple Lycoming it's impossible unless there is an oil dilution system.

[OntheNumbers]

@Photofly - thank you, no that's not it. I've been watching the dipstick like a kid waits for Christmas morning to see how many hours I get out of a quart after the recent overhaul. I anticipated adding a quart myself the next time I went flying, but it appears someone, or some-thing, beat me to it.

Regards,
OTN

[OntheNumbers]

@Ahramin, No, I didn't think there was, after 8 years' owning this plane it's never happened before. I'm familiar with the dipstick effect of the longer the engine sits after the last run the higher the oil goes up the stick. This looks like a gusher of oil by comparison!

One data point I forgot to mention is that the dipstick also got bent - and that suggests that someone actually added the oil, and bent the stick in the process. My AME recently replaced the throttle and mixture cables but says they didnt' add any oil, so that leaves those who have access to the hangar, and there are only 4; one is in the UK now, another was in the hangar when I saw the bent stick and the extra oil and didn't say anything. That leaves 2 others and I've no reason to suspect they did it.

Anyhow, thank you for your replies, they help eliminate a possible explanation. I'll investigate the social angle now.

Thank you again for your input

[ahramin]

Wow, that's pretty frightening. I'd drain the oil.

Ernest Gann told a story about someone sabotaging an aircraft by adding a quart of water to the oil.

[fish4life]

Does it smell like gas at all?

[digits_]

If they bent the dipstick, it makes you wonder what else they touched. Did you notice anything else off on your plane? Antennas, pitot tubes, static wicks, scratches, dents, ...?

[PilotDAR]

Oil can collect in a few places inside the engine (Continental starter adapters being one example) from which it won't all drain back to the sump - unless there's an unusual attitude/slip/G/turbulence bump. For half a quart, I wouldn't worry about it, you may find that it's relocated itself next time you check, and seemingly not there, just hidden again.

[OntheNumbers]

I didn't smell any gas in the oil when I checked, but will be sure to do that next time I'm at the hangar. The engine was only recently overhauled (50 hours ago now) so I tend to rule out gasoline in the oil.

@pilotDar, thanks for the note; I was hoping there might have been something after the overhaul that could have caused oil to be trapped somewhere like the oil cooler circuit (which makes no sense if you give it some thought). I'm not an engine expert, but I can't imagine where 1/2 quart of oil would hide - it's easier to imagine losing some to those two systems I mention, above.

I've spoken to everyone who has access to the hangar and none of them added any oil - and the AME says he didn't either, but I will ask him again. He's got two assistants; perhaps one of them cheked the oil, added a bit and stepped on the dipstick. Fearing a reprimand, they didn't mention adding the oil. If it's not that for sure, then I'll contact the police and report someone may have tampered with the aircraft, which, according to the big sign on the gate into the hangar area, "...is a federal offence".

I suppose an oil change would be a good idea too.

If the mystery ever gets solved I'll update this post for completeness.

Cheers all!

[Big Pistons Forever]

Are you sure the dipstick is the same one ? I know of one case were a dipstick was inadvertently swapped between 2 engine models during maintenance. The markings were not the same.

[nine sixteenths]

Are you sure the dipstick is the same one ? I know of one case were a dipstick was inadvertently swapped between 2 engine models during maintenance. The markings were not the same.

+1 to this. I’ve seen this before too.

[Heliian]

What kind of oil are you using and what were the temps when you checked it?

[photofly]

Are you sure the dipstick is the same one ? I know of one case were a dipstick was inadvertently swapped between 2 engine models during maintenance. The markings were not the same.

This was a Sherlock Holmes post, if ever I have read one. @BPF you should think about writing aircraft mystery novels

[OntheNumbers]

What kind of oil are you using and what were the temps when you checked it?

Aeroshell 100, I always check when the engine is cold - i.e. before flying. It had been 9 days since the previous flight, so plenty of time to settle down.

[OntheNumbers]

Are you sure the dipstick is the same one ? I know of one case were a dipstick was inadvertently swapped between 2 engine models during maintenance. The markings were not the same.

After the overhaul the dipstick has a yellow-painted cap and that is still the same. As for the markings stamped into the dipper, they look identical to before, but I suppose they are all stamped with the same die set. Good point, I hadn't thought of it! I'm gonna say it's the same stick with maybe a 90% certainty.

[flyguy73]

I will admit that I have no knowledge of this and if this is even possible, but does the oil cooler have a thermostat? If so, is it possible that some oil was in the cooler when you checked it the first time but not the second time?

[Heliian]

I will admit that I have no knowledge of this and if this is even possible, but does the oil cooler have a thermostat? If so, is it possible that some oil was in the cooler when you checked it the first time but not the second time?

Usually the cooler will take the oil in.

Check your hp fuel pump if it keeps happening, fuel could be leaking back into the case.

[AntiNakedMan]

What a mystery!

Re: different dipstick - most of the dipsticks I have seen with numbers stamped match the serial number on the engine. That should be easy to check.

Re: Bent dipstick - that’s a stumper. Why would the dipstick be near someone’s feet to be stepped on? Very odd.

Re: Increase in oil - 5.1 to 5.6 is interesting; who adds .5 at a time? Who has the time or patience for that?

Until you indicated a bent dipstick and the potential for interference, I would have told you that you may have mis remembered or you’re obsessing over a half litre.

So, did you solve the mystery?

Anti