General oil leak question...
 

I'm affraid this one may generate a response storm... I'm really just wondering what the conensous is on this.

I'm flying a 172 (O-320-D*). It's had a progressive oil leak that appears to come from around the prop. It's enough to mist the window after 2hrs of flying, but not a gusher. I've asked the owner to have it looked into, cause I really dont like flying long distances like this. He says it's coming from a bad silicon gasket seal around the casing and it's nothing to worry about.

My questions: Is any perceivable oil leak on a Lycoming reason enough for grounding? Is a controlled small and carefully watched leak ok to continue fly on?

-Bruce

BTW: If it where my plane, I'd rip the engine off and have it fixed ASAP, irregardless of the price. But that's me.

-Bruce

Maybe it's the crankshaft plug leaking.
A few years ago I rented a 172, got to my destination, slight film on windshield that was cleaned by the line crew. Next day at startup lost about a quart in the first minute, shut down and luckily there was a competnt A & P on that Sunday. He discovered the plug after rebuild (about 1-200 hours ago) was reinstalled after rebuild, with silicone to seal it instead of a new one. He did it right ....no more problem.
Hopefully your problem is as simple as that.

Could also be the front crankshaft seal. Make sure the crankcase breather is not blocked.

Oil on the windshield is something I would ground the airplane for and repair ASAP. I think I would look for another C172 to rent.........

Regards,

1 - I'm not renting, I'm being asked to fly as a favor. And there are not other planes around.
2 - This leak has been progressing for at least 6mo. Started out really mild, now it's noticable.

Life aint simple, tough decisions

-Bruce

Maybe pay for an A&P evaluation and, if the fix is not too involved, pay for the repair.
It'll probably still be a lot cheaper than renting and you'll be able to fly with peace of mind.

-mike

UV trace Check it
 

Clean the engine and use UV color dye oil leak tracer. You run the engine for a short period and look at it with a black light. This may not help here, but this may help others. A friend had an accessory case leak he could not find. The dye solved the mystery. It only takes a little oil to make a mess, even on the windshield. Fact is engines leak oil and most of it goes on the belly.

When you are flying one small oil leak can go all over, making it hard to tell its origin. The above assumption it is the fwd crank seal my be very true. Since it is in the front and oil should flow back, which should be easy to determine? The Gent you mention says its a case half leak. Could be? I agree you need to check it out. Full blown crank seals are kind of rare, not withstanding a blocked breather as was suggested to check.

The UV light thing works well. You add the dye to the oil and use a black light. You need to clean the engine and than apply the leak detector. There are external UV detectors that react to oil, but the engine has to be very clean. I think it drys like a light powder.

The dye step may not be necessary if obvious, but it sounds like you have some doubt where it comes from. This method will tell you. You need to ground run for only a few minutes for obvious reasons, because if you go flying and oil goes all over the dye thing will not work. In any case caution and care should be taken. If you judge it's not airworthy, don't go flying. With they dye chack you can do it on the ground.

George

George,
You really don't need the dye! Little known fact is the oil shows up really well in it's natural state. All of the oil leaks, I have used a black light to trace, have shown up great under the black light without the dye. Using a black light is a very good way to go, when troubleshooting a hard to find leak. We use that process all the time in the shop here. Another method is to clean it up and spray white dye penatrant developer around the suspected leak. Run the engine and the oil will show in the developer really well.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at you own risk."

Never needed it
 

Thank you, most excellent info. I never used the (external) dye, but it did help a friend (who I was helping) find a mystery leak. With oil already all over and hard to clean the external marker was not as practical, BECAUSE the accessory case had so much oil on it, cleaning was difficult. The oil additive worked better here. He could never find the source till he used the oil dye additive. Those other techniques are cool. I have heard of the applying the external markers, but in this case the additive to the crankcase was best. If I ever have a leak I'll try the external method. George

ed - to clarify that I did use crankcase oil additive and the oily condition of the engine, location, accessory case, it was not practical to use the external UV indicator.

follow-up
 

The owner had his mechanic reset the silicon case seal. It's stopped leaking and I can go back to day dreaming while I fly.

-Bruce