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Oil on top of Airbox

Drippy

Well Known Member
Friends,

I am trying to chase down a leak and wonder if any of you have ever seen a simliar oil trace.

I am getting oil on my airbox and it appears to be leaking from the throttle body. The interesting thing is the oil almost has a greenish tint.

AF1QipMYKuojz6vRcGubhnrjTL8CUgPVHU0iKHS0hzBw


Engine: IO540 C4B5~ 500hrs - but I believe the leak has been there since day one.

Thanks for any suggestions.

https://photos.google.com/share/AF1...?key=bW41dmNWMWZrSUlsSGpsNmNWZmx2Y0RpSkVCOHVn

Mike
 
It is leakage from the intake guides. Oil from the rocker box is sucked, because of the lower pressure in the intake ports, through the intake valve guides, lubricating the valve stem. This small amount of oil gets burned while the engine is running at higher RPM during flight. While at idle, during taxi, the suction is higher than in flight causing this residual oil to run down the intake manifold into the air box. If the seal between the airbox and the fuel servo is not perfect; oil will seep out onto the airbox's top plate.

Of course if the intake guides clearance is excessive; more oil is sucked past the guides than is needed, and the guides would need to be replaced.

The green tint is because the oil is mixed with 100LL percolated out of the fuel divider after shutdown.
 
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Airbox seal

Thank you for the info.

Just making sure I understand - even if I correct the seal between the throttle body and airbox I am still going to consume the oil it is just going to get burned next time I am at high RPM?
 
Any crankshaft seal votes?

Any votes to check breather routing?

Mine dried up with breather routing improvement.

It was NOT pushrod seals, didn't touch the crank nose seal.
 
There is a florescent dye you put in the oil and use a black light to find it. However you should degrease and engine first. Check everything is snug, the valve covers, oil return line clamps, accessory clamps... Did you spill oil filling it? Sometimes that ends up in the bottom of the cowl.

A ground run may be in order first. Put cowl on to keep oil from being blow around too much. Try to get engine to full operating temp.

If you don't see leakage from dye indicator after a ground run or three, go fly, short flight or pattern with engine up to operating Temp. De-cowl and look for dye trace. If you go fly oil may blow around and make source hard to find. Clean engine and cowl as suggested above before looking for leak. A small leak can make a big mess over time.

Oil can come from many places, push rod tubes, rocker cover, oil return lines, main front seal, accessory case, accessories, oil pan, crankcase halves. Leak does not have to be right over airbox. Oil clings to engine case and flows around. Air flow under cowl in flight can be a tornado in many directions causing oil to migrate away from source in many directions. Typically airflow and gravity causes flow to be down. After that it can be a challenge to pin point.

Then what? If you find a small leak it may be best to leave alone. Many engines leak. Wing tanks leak fuel on large aircraft. There is an acceptable leakage. Put a pan under engine when parked and look how much is hitting the floor. Is there an oil film on belly or is it dripping off. I took my vacuum pump off and put a DIY blocking plate. It was not sufficiently sealed. One flight oil was dripping off the belly. I lost at list 1/2 qt. in short order. Reason for short flight test after maintenance. Have you removed and installed anything recently?

Lycoming, if no oil is leaking out of it there is no oil in it. (Paraphrase radial engine saying, same applies to old British Sports Cars and Motorcycles. Some may argue they are not leaking. They are simply making their territory.)
 
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oil fluoresces all by itself. Find out for yourself by shining a black light on some in the dark.
The additive does make it brighter though.
Art
 
Lycoming, if no oil is leaking out of it there is no oil in it. (Paraphrase radial engine saying, same applies to old British Sports Cars and Motorcycles. Some may argue they are not leaking. They are simply making their territory.)
Yep! That reminds me of a funny comment from our T-28 mechanic; “even British televisions leak oil.”… it’s probably true.
 
Bead your tubes

Friends,

I am trying to chase down a leak and wonder if any of you have ever seen a simliar oil trace.

I am getting oil on my airbox and it appears to be leaking from the throttle body. The interesting thing is the oil almost has a greenish tint.

AF1QipMYKuojz6vRcGubhnrjTL8CUgPVHU0iKHS0hzBw


Engine: IO540 C4B5~ 500hrs - but I believe the leak has been there since day one.

Thanks for any suggestions.

https://photos.google.com/share/AF1...?key=bW41dmNWMWZrSUlsSGpsNmNWZmx2Y0RpSkVCOHVn

Mike

I had a similar problem and the leak was coming from my drain tubes. I beaded my tubes pursuant to Dan's KP article and used constant pressure clamps and everything is now dry as a bone.

https://www.kitplanes.com/to-bead-or-not-to-bead/

Hope that helps.
 
Oil pan leaked

I had a small annoying leak that urned out to be the oil pan gasket. Like others have said, it can be almost anything.
 

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Green?

As others have mentioned, I have had good luck with my HF blue light flashlight in a very dark hangar. The oil is easy to see.

My theory as to why it’s green? If the sort of yellow clean oil mixes with the kind of blue 100 LL dye, you have green. A potential clue?

Good luck, Jim
 
I Agree with Boyd

wonder if any of you have ever seen a simliar oil trace...
…the oil almost has a greenish tint.

I think Boyd called it. I had the exact same greenish oil on top of my FAB. RV-4, IO-320. Some previous owner drilled a #30 drain hole on the aft top of the FAB at the low point of where the tiny puddle would form. The hole is outside of where the filter seals. I learned of this phenomenon and fix when the drain hole plugged up leaving the puddle for me to find.
Yes, any oil in the intake tract from this source will be harmlessly ingested.
 
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I have the same 'oil on the top of the airbox issue', tinted green. Not a lot, but more than I'd like - makes a mess. I would agree with Boyd as to the cause, and a well-respected RV expert in my area told me the same. But I'm confused about the #30 hole for a low-point drain. Where does the oil go once drained through the #30 hole? Doesn't it just go back into the airbox, albeit outside of the filter OD? It would still be a 'leak' and need to be cleaned up occasionally, wouldn't it?
 
It goes into the airbox where it is ingested harmlessly into the engine. It is a minute amount of oil.
Since my -4 is a tailtragger the low point of the FAB top is the furthest aft point.
I see you have a -9A so the horizontal top of your airbox might not really have a low point. I can see how a lot of oil would build up and start making a mess.
In my case the oil residue on top of the FAB stays there and doesn’t make a mess.
I replaced the gasket at the top of the FAB but a tiny amount of residual oil via the intake guide still finds it’s way out.
 
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It's been a bit, but I don't recall a gasket at the top of my FAB (between the FAB and the servo?). But I’m sure if there is supposed to be one there, it is - yeah, right! But I’ll check and replace it if necessary.

Thanks for the input.
 
Air Box Gasket

Thanks for all the good information. I am currently mid-cross country adventure avoiding the cold of New England and watching a little baseball in FL.

I too don't have a gasket between the airbox and the throttle body. That may be causing some the the oil to seep out. I may try putting something there when I get home, realizing that is just keeping the oil in, but not reducing the amount of oil through the motor.

Once again thanks for all the help.
 
OK, it turns out I don't have a gasket between my airbox and (Precision EX-5VA1) servo. Does anyone happen to know a part number for this, and/or where to get one?

Thanks!
 
I've been chasing and oil leak for a few months so was interested in this thread. I do like Boyd's explanation as the colour change would have no other reason that fuel contamination.

I had a red oil under my plane with surprised me until I remembered I had re-oiled my filter whilst waiting for the cylinders to come back and the K+N oil was being washed out by my over priming.

So I'd go with the guides though that would not be my preferred problem.

Good luck with it, a bit of oil loss can not actually be a problem at all of course.
Mike Busch says 'oil is cheap'.

Regards, Clive
 
Make Gasket

OK, it turns out I don't have a gasket between my airbox and (Precision EX-5VA1) servo. Does anyone happen to know a part number for this, and/or where to get one?

Thanks!

I cut my own from a sheet procured at Auto Zone
 
Thanks for the Airflow Performance link. I should have known to check there, that's where I purchased a modified mixture arm.

Gotta love this forum!
 
I've been chasing and oil leak for a few months so was interested in this thread. I do like Boyd's explanation as the colour change would have no other reason that fuel contamination.

I had a red oil under my plane with surprised me until I remembered I had re-oiled my filter whilst waiting for the cylinders to come back and the K+N oil was being washed out by my over priming.

So I'd go with the guides though that would not be my preferred problem.

Good luck with it, a bit of oil loss can not actually be a problem at all of course.
Mike Busch says 'oil is cheap'.

Regards, Clive

I had a small oil puddle (all dark engine oil) on top of airbox. 1st I found the intake return hoses and crappy serrated clamps were toast on 2 of them. Changed all 6 to constant force clamps and replaced all hoses with higher temp rated Pegasus hose (PN 3290-6), cut pieces of 1 1/2" length. Seemed fine for a couple flights. Now, oil is back and I am unable to see the source. Maybe clean and try the oil dye.

After removing the cowls, and a few cleanings around the oil pan, I found the oil pan bolts would torque @1/8 turn at spec 96 in/lbs. This solved 80% of the leak around the oil pan. Another cleanup and went 10/11% to 110 in/lbs. Fired up to temperature, shutdown and no leaks. I’ll take a short test flight and check again.
 

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