Seeking Advice on Diagnosing Oil Consumption

[OntheNumbers]

Oil consumption on my 1969 Cardinal seems to be on the increase. It used to be 1 quart every 5 to 6 hours or more but it has dropped below 1 in 5 hours. Besides the dipstick level dropping faster than usual, the only other symptom is a lot of oil on the inside of the engine cowling on the pilot's side. The inside surface has a large area shining in the light from its coating of oil. Oil also comes out from under the left-side and small spots of it end up on the left main gear leg.

Recent work in this area was 6 months ago, re-plumbing the oil return lines from the cylinders. The problem had been happening well before that work was done, and after the work was done the problem was the same (or maybe even worse). Rocker cover gaskets were also all replaced. Running a finger inside the exhaust stack you get a very nice light grey dust, no gooey oily feeling at all - so if it's burning oil, it's not burning enough to gunk up the stack. Obvious places like the dipstick tube (which is on the other side of the cowling) look dry.

I want to fix the problem but budget is limited so a major objective is to learn as much as possible about diagnosing this kind of problem to help reduce the costs somewhat. I don't plan to actually try and fix it myself but if it's possible to pinpoint the problem on my own time, that might be worth it. I'd also like to be able to understand anything the AME tells me and decide on the likelihood of that scenario before pulling the trigger on getting it fixed. A friend of mine recently dropped $25K to have his engine rebuilt in the hope it would stop a pesky vibration he noticed while flying. It didn't make any difference except to his bank account.

An oil leak is maybe a little easier to diagnose.

If anyone can offer any advice, thoughts they'd be much appreciated and I'll eventually post the solution to the forum once it is known.

Cheers

[photofly]

the engine cowling on the pilot's side. The inside surface has a large area shining in the light from its coating of oil. Oil also comes out from under the left-side and small spots of it end up on the left main gear leg.

You have an oil leak.

Wash the engine and bay throughly with gasoline or varsol. Run for 10 mins and try to find the source - something needs tightening.

An oil leak needs to get really serious before it shows up as increased per-hour consumption though!

A friend of mine recently dropped $25K to have his engine rebuilt in the hope it would stop a pesky vibration he noticed while flying.

You're kidding, right? Was the vibration connected to the rotation of the big fan up front? If so, it could be bad, really really bad... Also tell him I have a friend in Nigeria who needs a partner to shift some orphaned cash.

[ahramin]

Has your AME not suggested cleaning everything thoroughly and spraying developer on it? It sounds like you are scared to simply drop the plane off and say fix it because of the budget, but that's a bad idea for any budget. Your options are not limited to figure it out yourself or get hosed.

Instead of asking these questions on an anonymous forum, discuss this with your AME and come up with a solution that works for both of you.

[crazyaviator]

Excessive oil burn/blow-by will show up in the lower plugs ( wet and fouling) before you see that I suggest you don't worry about internal consumption. Externally, oil leaks are mostly a nuisance , can come from most anywhere and look like more oil than it really is! The excessive oil on belly from the breather is a good sign of impending internal cylinder wear

[cgzro]

1-Take the cowls off, clean them inside and out.
2-Then wash the engine, firewall, plane etc.. You can use varsol or mineral spirits in a spray bottle.
Be careful not to get any on the rubber engine mounts.
3-Clean as much as you can, with paper towels etc.
4- Now re-cowl and go for a very short flight say a circuit with high power on downwind.
5-De-cowl and have a good look everywhere with a mag-light or such.

This is likely the first step your mechanic will do and it takes a few hours so you just saved a few hundred bucks.

[OntheNumbers]

@Ahramin - Understood. However the AME is not responsible for the airworthiness of my aircraft; I want to learn as much about my aircraft as possible and this is a good opportunity to diagnose what is, by all accounts, a particularly elusive problem. This forum advertises itself as a place to discuss maintenance issues and that's what I thought I was doing. Finances are a secondary consideration and rather than give an AME carte blanche to go ahead and find the problem, I'd rather have a very good idea what the problem is and ask him to confirm it and provide a quote to repair it. As Photofly says, somethings loose and I want to find it. Then I'll pay a fair price for whatever it takes to fix it.

I was actually hoping (against hope) there was a way other than washing the compartment and engine with Varsol or Mineral spirits; I have big hands and it won't be easy to get into all the nooks and crannies. Since Photofly and CGZRO have kindly suggested a similar course of action, I'll give it a try. I've also heard of some kind of additive that glows in UV light - would be interested in hearing about anyone's experience using that.

Forgot to mention, this engine has an Airwolf separator but still gets lots of oil on the belly as I noted above. Two of the bottom plugs have accumulated oil since I bought the plane but they've been cleaned and swapped top for bottom regularly.

Anyhow, thanks for all the responses - I'll have a go at cleaning off the oil (and will mind the rubber parts in the process, thanks CGZRO).

-- otn

[Kejidog]

I have a C172 with an O300. I was told if it don't leak that means it's out of oil.

I recently went on the hunt for my leaks. Did the cowl removal and clean up routine. I found I had a magneto that was leaking oil. We removed it had it repaired then put it back on and most of my leak stains went away. But i still have a drip from my oil quick drain. That will be addressed next change. Also my pushtubes seem to seep a bit of oil into the cowl.

A small leak can look like a real mess and finding it is a pain. I like to have stuff just so so i am still keeping an eye on the inside of the cowling.

And doing the cleaning routine is a great way to show the plane some love.

[Greysierra]

Finding oil leaks can sometimes be tricky as just a little bit of oil can make a big mess. As stated above, my first course of action would be to remove the cowls and give the engine a good cleaning. Here in the shop we will often use break cleaner in a hand pump. As also mentioned above be careful around rubber mounts and electrical items such as the alternator, starter, etc. I would give the engine a short ground run to build a bit of oil temperature without the cowls and immediately after shut down check for leaks.

The cowl stains can often tell a story as to what's going on around the engine. Stain locations and patterns can sometimes help to pinpoint possible leaky areas.

I'm not sure what type of engine is in a Cardinal... however, Id have a good look at magneto, starter and/or vacuum pump mounting pad gaskets, rocker box cover gaskets, and oil drain return lines. I've seen on a few occasions the baffle springs shift and wear through the lower rocker box oil return lines. Also have a close look anywhere a rubber line is connected with a hose clamp.

additionally, you could check your lower spark plugs as well as completing a engine cylinder compression check if you feel that the engine may be burning the oil. These checks could help to determine if the oil is creeping past your piston rings or past the intake or exhaust valves.

Hope this helps and best of luck.

[crazyaviator]

A spray wand is about 14-18 inches long and curved at the end,,, ideal for spray washing,,, I also use 100LL . Remember to spray thoroughly and blow dry for about 10 minutes. Any real leaks will be all over the place and near impossible to discern if you do a circuit !

[robertw]

Please whatever you do, don't clean your engine with 100LL or other gasoline. Fuel is for burning in engines. All you need is a little static electricity or other small spark and BOOM! You won't be worrying about an oil leak any more...

Use varsol, it's for cleaning oily parts.

[crazyaviator]

All you need is a little static electricity or other small spark and BOOM! You won't be worrying about an oil leak any more.

You know, that has got to be the simplest, wisest, and most "spontaneous" answer I have heard in a long time! I will take that to heart!
I take back my suggestion about using 100LL and rather recommend a good insurance policy and TNT !

[crazyaviator]

I mean really, What was I thinking !!!

[cgzro]

Common but harmless and cheap leaks are things like mating surfaces and the gasket between them. So all the valve covers, oil pan, accessory case attachment bolts. Case half bolts, dipstick tube. Most of those will losten up every hundred hours or so and take a 1/4 turn or so.

More serious are little grey lines in the case that are actually leaking cracks. looks like a pencil mark against the paint. These ususally require a rebuild because the end result is catastrophic. Dangerous ares for these little grey lines in particular are near the cylinder hold down bolts.

The front seal can also be a problem and dangerous, its the seal where the crankshaft exits the case. Youll get oil everywhere in this case and it can be minor or serious but needs to be investigated properly if its happening.

Probably something trivial but good to know whats serious and whats not, especially in an IFR machine you put your family in.

[robertw]

Best thing to do as stated in a few other posts is to de-cowl your engine, spray wash with varsol, wait until dry and run the engine for a while. Oil leaks should be easy to spot on a clean engine.

It's strange that your Airwolf oil separator does not keep the oil off the belly. Are you sure it's installed correctly? Are the lines clear and flow to and from the crankcase? Are they in good condition? I'd have a really good look at the system that's supposed to keep oil in the engine. You might want to give them a call to get their opinion as to why it's not working correctly.

http://www.airwolf.com/aw/

Let us know what you find.

[OntheNumbers]

It sounds straightforward but there's rubber everywhere so spray carefully, use Varsol or Mineral Spirits, I assume some wiping is necessary but will be hard to do in the remote parts of the engine, otherwise allow the solvent to dry naturally. Don't use gasoline (does anyone remember the guy at Cambie and Broadway in Vancouver who tried cleaning his pizza oven with gas with predictable results?) Look for little grey lines in the case and make sure the front seal is not leaking - probably (hopoefully) not, it was checked 2 years ago at annual.

Thank you all for the encouragement, I'm pumped to go find where the oil's getting out!

Best Wishes,

-- otn

[crazyaviator]

otherwise allow the solvent to dry naturally

varsol takes forever to dry and WILL mix with any fraction of oil when leak checking,,,, best to BLOW DRY ALL varsol this will remove any solvent from rubber parts as well !

[OntheNumbers]

I've got an update on this topic.

In the summer I use Aeroshell 100+ and in the cooler months I switch to Aeroshell 80+. It always seemed like oil consumption was worse in the summer but I never had any way to quantify it. Sometimes it seemed OK and other times it seemed bad - didn't make sense. This year a buddy of mine has been using the plane so it's been getting more use with shorter rest intervals between flights than it would have had with just me flying it.

Recently the plane was flown to the Nanaimo fly-in breakfast (1 hour total airtime) on Sept 2 and before the flight a quart of oil was added pre-flight - dipstick was showing ~5 quarts before that. Two days later the plane was flown to Tofino and back and no oil was added but a note in the logbook shows the dipstick read 5.5 quarts after just 2.2 hours. A couple of days after that flight I dropped over the hangar and checked the stick and saw around 5 quarts. Total airtime up to this point was 3.5 hours - so it looked like 1 quart disappeared after 3.5 hours.

On Sept 16th I took the plane for a flight in two segments totalling 1.2 hours. Before the flight I checked the stick and was surprised to see it at a healthy 5.5 quarts! I think what had happened was during the 12 days since the previous flight the oil that was clinging to the interior of the engine had mostly settled back into the sump causing the stick to read an honest value.

The next day I went back to the hanger to start cleaning the engine as described in this thread; the oil read below 5 quarts.

The plane is grounded for the time being - engine cleaned now and I'm letting it sit, cowls off, without a run-up to see if any oil voluntarily appears anywhere. After a few days I'll go have another look and check the stick again. I bet it will be above 5 and if I leave it long enough it will be interesting to see how much oil really is in there. I'll check the engine for any signs of oil weeping out anywhere. If none is seen I'll run the engine for a few minutes and check again.

Long story short - although there's a leak, the apparent increase in consumption is due to the shorter time interval between flights and the longer time it takes the more viscous oil to settle back into the sump.

I will update the post with the results of the cleaning and subsequent inspection.

[photofly]

Just to remind you, enough oil to only just make a visible difference on a dipstick (say 1/4 quart) will make a stunning colossal unmistakeable "wtf-is-that" mess all over the inside of the cowl or on the hangar floor. A tiny bit of oil goes a long long way, and an engine that leaks enough in flight to cause a well-founded concern about oil levels will be an ecological disaster when you land.

Mostly the "used" oil leaks out of the crankcase breather all over the belly or gets burnt and sent out of the exhaust.

[LousyFisherman]

There is no point checking the oil in the dreaded C150 other than first thing before starting the engine. It takes a long time (more than 6 hours, IIRC) for the oil to drain into the sump.

HTH
LF

[OntheNumbers]

I had some help from a friend - last weekend (Sept 18th) we cleaned off the oil from as many places as we could reach using a long artist's paint brush (14") and some rags. For parts the rags couldn't reach my friend's air compressor was handy for drying the mineral spirits and oil. Later it felt dry and not greasy to the touch. We did not run the engine, deciding to see if any oil wept out anywhere without the engine running.

On Friday I went back and checked the engine. Everything remained clean except for one place where the sump bolts to the bottom of the O360 and at the front. Here's the shot as of the 17th followed by the shot after 5 days. The black shape on the right side of the images is the starter. In other words the leak faces the front of the aircraft.

I cleaned the area and went for a short flight today, circuits for 0.4 and removed the cowl for another look. It was messy again and more than what appears in the photo after the engine had been through 4 circuits. Other places still looked clean.

Looks like the leak is either from the sump's (correct term?) seam where it joins the crankcase or perhaps the split line of the crankcase. Seems more likely the sump which has a gasket visible (black line in the photo).

[Edit] - Figured out how to add images. Before and after shots: