Oil stains on exhaust

[Derrickearly]

I have some oil stains on cylinders 2 and 3 at the exhaust. This is an io390 with about 250 hours. Any ideas?

[N201MKTurbo]

Might be from your push rod shroud tubes.

[N201MKTurbo]

Are you sure it is oil? You might have up-chucking injectors.

[StevenL757]

It certainly looks like oil around that nut on the right side of the last photo...no blue staining there.

@Derrickearly, I would clean up the area, replace the gasket, re-torque the nuts to spec and run the engine again.  Depending on when all the gaskets were changed, it might be a proactive move to do them all.

Steve

[A64Pilot]

What do the plugs look like?

[Derrickearly]

17 minutes ago, A64Pilot said:

What do the plugs look like?

The plugs are good. 

[Derrickearly]

48 minutes ago, StevenL757 said:

It certainly looks like oil around that nut on the right side of the last photo...no blue staining there.

@Derrickearly, I would clean up the area, replace the gasket, re-torque the nuts to spec and run the engine again.  Depending on when all the gaskets were changed, it might be a proactive move to do them all.

Steve

If I replace the gaskets, could this hide a problem by keeping the oil inside the exhaust? Will a leaky valve guide show through even a good exhaust valve gasket?

[takair]

I was initially thinking fuel too, but I see oils on the nut.  What I don’t see, or I’m looking wrong, where is the gasket?  Are they just the thin brass style vs the no-blow?  The oil can come from the valve but it would usually burn on the exhaust side and not leak out.  Makes me suspicious of a crack in the cylinder, but even that would be unusual...like that.  Certainly deserves investigation.

[A64Pilot]

Clean plugs pretty much rule out excess fuel and or a broken ring consuming too much oil, which does seem to indicate a leaking valve guide seal, because what else is there?  Cracked head is a disturbing thought, could be I guess.

I don’t think push rod tube or valve cover myself, it seems to be coming from inside of the exhaust.

‘OEM gaskets are thin sheet steel, but the gasket isn’t the problem, meaning putting new ones in won’t fix the issue, maybe hide it.

‘Have you done a cylinder leak down test? Unless it shows something I believe I’d pull the cylinder and take it to a shop that overhauls them, and have them inspect.

[EricJ]

Look up at the side and top of the head to see whether that oil is coming down through the fins.   On many heads, angle valve in particular, there's a small access cover higher on the head for the rocker shaft.   If that leaks the oil will dribble down to wherever.    I've had weird oil traces show up under my cylinders, too, and there's a ton of potential places it can come from.   I think it's unlikely to be coming from inside the exhaust port, but who knows.   It may just be blowing drippy oil from somewhere else around during startup before the gasket seals completely.

 

 

[takair]

#3 also might have an exhaust leak blowing near the spark plug...  What does the inboard side of the stack look like?

[EricJ]

Here's a pic to look for toward the upper part of the cylinder.   The two little covers are for the rocker shafts, and also inspect around the ends of the pushrod tubes for leaks that are dribbling down through the cooling fins.

 

[SSimpson77]

I think @N201MKTurbo has a possibility there. If it was blue it has the wicking and drip rate as if it were 100LL. When it heats up, pyrolysis turns it black. Clean it really well and do some ground runs. Maybe put a GOPro mounted near drip and record while doing run-up

[carusoam]

That is a fair amount of staining...

If it were fuel... there would be blue traces and spattering all over the place...

Does it have an aroma?

Maybe it is fuel, under ideal conditions... so... use a white towel and wipe some of the grime...  no hint of blue? It’s oil...

+1 for checking those small ports... there might be a screw missing for that much oil...

PP thoughts only, not a mechanic...

Let’s invite @M20Doc to stop by (interesting oil leak on. Cylinder of an IO360)

Best regards,

-a-

[Gagarin]

This oil stain appears to be from a leak above that drips down after engine shutdown. Check the push rods shroud tubing O-rings.

Jose