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The art and science of chasing oil leaks

LettersFromFlyoverCountry

Well Known Member
oil_leak.jpg


I buttoned up at the airplane after the annual and took it out for a run up and high-speed taxi on Saturday, then noticed a line of oil coming down the gear leg.

The engine has always been a little weepy around there -- I'll never stop the occasional drip coming out of the oil screen plug (at least by following the torque instructions for it . I've got oil around the hex plugs (and the one with the square underneath it on the oil sump that I don't use. I've tried tightening them and they're tight but they still weep (I wonder if some Fuel Lube/EZ Turn would help?).

But this latest leak shown below seems to come from the cover just to the left of the oil return (I have the thing plumbed for CS but I'm fixed pitch) and where it meets the case itself.

I put a wrench on the four nuts here (for orientation, you're looking straight up from the bottom and the studs point straight aft. Oil sump lower and left side) and they weren't loose, really. I could turn them slightly with a bit of a pull. And I couild do the same with the nuts where it attaches to the case.

A couple of questions: (1) Does an engine tend to leak more when it hasn't been run in almost three months? And if so (2) does the leak subside somewhat? (3) What is the art of slowing a leak like this? and (4) What is the point at which you say, engines are dirty things and the I can live with some oil?

This engine does not use much oil. Of course it doesn't run for long periods either. Tops is a couple of hours. If I throw a quart in every 12 hours, it wouldn't surprise me to learn a lot of it is thrown overboard via the breather tube.

BTW, I'm really sorry I ever put a whistle hole in the breather tube. With a 7A, it's almost impossible to bend the breather tube to drop the oil over the exhaust stack... the engine mount gets in the way and the the whistle hole just sends the oil every which way.
 
Clean up the oil on the engine and then use some spray foot powder / spray talc on the suspected areas. Run the engine - oil leak sources show up well.

Depends on where the leak is, but there are some parts of the motor that no amount of tightening will solve the problem - you have to address the leak in other ways depending on where the leak might be.

On gaskets, I use the EZ turn. I rebuilt an O-360 and used EZ turn on just about everything except the case halves, cylinder bases, oil filter and the gasket for the oil filler tube. Driest engine I've ever had.

(Consider a piece of flat sheet - a left over aluminum piece - and put a glob of EZ turn on it. Spread it out with one of those 4 or 5 inch rollers like in the craft shops. Lay the gasket on it, roll some more. Flip the gasket and roll again. Where you'll really like this is when someday you have to take it apart.)

Dan
 
Bob, regarding the leaks around the oil screen plug and sump drains:

1) Do you replace the crush washer each time you remove the oil screen plug? These are meant to be replaced every time.

2) On any tapered thread plugs, including the square-headed oil sump drain plugs, a good thread sealant needs to be used here. Not fuel-lube/EZ-turn. I like Loctite 567 for tapered pipe threads. Some like Permatex #2, some like Titeseal. I'm sure there are others, but fuel lube/EZ-Turn is not a sealant and will leave you chasing leaks on threaded fittings/plugs.
 
Bob, regarding the leaks around the oil screen plug and sump drains:

1) Do you replace the crush washer each time you remove the oil screen plug? These are meant to be replaced every time.

2) On any tapered thread plugs, including the square-headed oil sump drain plugs, a good thread sealant needs to be used here. Not fuel-lube/EZ-turn. I like Loctite 567 for tapered pipe threads. Some like Permatex #2, some like Titeseal. I'm sure there are others, but fuel lube/EZ-Turn is not a sealant and will leave you chasing leaks on threaded fittings/plugs.

I do change the crush washers, yes. Good tip on the 567. Will use at next oil change. Assuming i can get enough hours on this thing to warrant an oil change. :*)
 
I do change the crush washers, yes. Good tip on the 567. Will use at next oil change. Assuming i can get enough hours on this thing to warrant an oil change. :*)

Bob, I like Permatex #3 (#2 could work too) on a problematic crush washer. If this does not work, look closely at surface finishes, and flatness of contact areas.

If an engine leaks it is to be repaired. I was not designed to leak.
 
The crush washer has to be installed turned a certain way - I don't remember which side goes which way and usually have to look it up in the Lycoming manual.

I chased oil leaks on my IOF-360 for a couple years off and on. It always drained down the nose gear and I usually found most of the oil on the sump bolt above the sump screen and on the sump screen bolt. I could wash the engine down, run it up for 10 or 15 minutes with no leaks anywhere. Cowl it up and go around the pattern and the oil would be back on the gear leg. To make a long and aggravating story short it turned out to be a leak around the threads on the elbow going into the back of the engine from the oil cooler hose. I used die in the oil and still couldn't find it until one day I ran the engine for about 30 minutes and got the oil up to 165*. I found the leak around the pipe threads which didn't have any thread sealer on them. After I found the leak I realized why I never found it before - I wasn't running engine long enough to get hot and start sending the oil through the cooler and that elbow fitting. Some good sealer on the threads took care of the problem.
 
2) On any tapered thread plugs, including the square-headed oil sump drain plugs, a good thread sealant needs to be used here. Not fuel-lube/EZ-turn. I like Loctite 567 for tapered pipe threads. Some like Permatex #2, some like Titeseal. I'm sure there are others, but fuel lube/EZ-Turn is not a sealant and will leave you chasing leaks on threaded fittings/plugs.
For tapered thread fittings (like oil cooler hoses), I found Permatex High Performance Thread Sealant to be the fix. Permatex High Performance. I could never find the equivalent Loctite product at local stores (567 or ?).

I had a small leak at an oil cooler connection that I worked on several times over 100s of hours. The High Performance sealant is ideal - sets up instantly (100% cure in hours), seals absolutely, parts come apart without any extra effort. White tube, blue lettering.
 
This is a very interesting -- no pun intended -- thread. I don't know why I didn't know anything about putting Permatex on the threads.

I did check the connections at the cooler and engine for the oil cooler, but I'll check once more.

(Also, if memory serves, split in the crush washer goes against the engine case)
 
multigrade oil

A couple of annuals ago I had some seeps around the valve covers, which I chose to watch only. I had used a multigrade oil on the prior change. I went back to straight 50w and the leaks cured themselves. Desert living has its advantages sometimes.
 
I've found I always have oil drips on the square NPT plugs on the bottom of the sump and a few other places like the bottom of the alternator bracket, I believe the oil from the breather is swirling forward and finding these spots. I'm planning on redoing my breather and making the hose higher, I haven't run my engine in a month and I'm still getting drips out the breather.
 
There is a product called SlapShot (how Canadian) by Walter that Grainger sells and probably many others. It is a spray cleaner that dissolves oil away. If you have a leak you spray your engine with this and it will be pristine, then you can run it for a short time and check with talc, or dye penetrant stuff or spray developer or whatever to look for evidence of leaks. It doesn't wash it all onto the floor either - it somehow evaporates. It's probably full of everything you can imagine that ends with "ene" like tolulene, benzene, etc etc. But works great. My engine rebuilder friend buys it by the case to clean off engines and troubleshoot in the field.
 
Oil and gas leaks

Tack & Seal by permatex is to be used on oil and fuel fittings or problem leaks such as oil cooler fitting. White in color, does not harden and parts come apart with no effort. The Kifox people turned me on to this when I could not get the header tank fitting to stop leaking.
 
Dan Baier had a great idea. Clean the engine and spray it with foot powder, run up the engine and check.

I did, and found that areas I thought were leaking weren't leaking (except that stupid breather tube puking stuff, and the oil strainer plug, of course).

oil_leak_3.jpg


I did find an area in the front, at the case split.

oil_lead_feb_27.jpg


Very difficult to get wrenches in this location although I did, sort of. The nut and bolt was tight, leading me back to the original question of when is a sign of oil a problem and when is it just the way engines are?

More here.
 
I did find an area in the front, at the case split.

oil_lead_feb_27.jpg

Exactly where my brand new Titan O-340 has a small drip once in a while. After checking torque on the two bolts shown, I've accepted it as not a big deal because I'm very happy with the low oil consumption of this engine. A couple drops can look like a huge mess because it just gets blown around everywhere, as you found.
 
I've found I always have oil drips on the square NPT plugs on the bottom of the sump and a few other places like the bottom of the alternator bracket, I believe the oil from the breather is swirling forward and finding these spots. I'm planning on redoing my breather and making the hose higher, I haven't run my engine in a month and I'm still getting drips out the breather.

.. The drips on the oil plug are most likely due to a standard pipe plug being used. The plugs that are designed not to leak have a rolled thread, are made of steel (not cast), and are designed to not leak and require no sealers at all. We just happen to have them available on our website. Thanks, Allan..:D
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If you don't have to put a drip pan under your cowling, it ain't leaking ;)
Don't drive yourself too crazy....
 
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