The International Cessna^® 170 Association

Kind of an oxymoron I am getting green oily drainage from my intake. My carb. mech. thinks I am getting condensation of fuel vapors in the intake system and then they are running down through the carb. I have had some recent problems with my carburetor float valve not seating right and so allowing the bowl level to get too high and leak slightly (which has been corrected). The green oil problem shows up after the engine is run - I am thinking that is does it at low rpms. Do any of you have experience with this problem? Any ideas on what the cause is? Thanks for your help!

I don't now about the "green" but the "oily" could be a leak in the oil pan. These usually corrode from the inside out just forward of the carb.

This might give you an idea, I have a somewhat similar problem with an oily drip coming from the bottom of my airbox. 0-200 Continental. Folks seem to think it's a worn guide. Good compression so that's not a 'guide' indicator apparently in my case...

A whopping problem I had with my Marvel carb was too much use of the accelerator pump on starting, and this caused a real issue with fuel coming out of the airbox, mixed with apparently the oil from the supposedly leaky mystery guide. Change of starting technique and life is much better.


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Thank you for the ideas. Besides the dread of having to replace the oil plan I don't think the oil pan has a leak - or at least that hopefully isn't what is causing the problem because it only leaks after it has been running. Valve guides make sense. It only has about 800 hours on the top overhaul - how hard is it to replace intake guides?

- how hard is it to replace intake guides?

Very. I'd remove the intake tubes (which might mean dropping the carb and intake spider) to see if an individual intake guide was causing the problem. Just look for the oiliest intake tube. I've been dreading doing this myself, especially since I have no leaks on the tubes themselves! Assume you have an 0-300/c-145? I'm no expert there but appears to be somewhat similar to what I have (with 2 extra jugs...).

For a thought (and I'm no engine expert) but you can pop the intake valve springs on each jug and have your mechanic check for 'wobble' (don't lose them down inside the jugs!), maybe one is worse than the rest. Just a thought, might narrow things down a little. Easier than removing intake tubes.

Intake guides are something for cylinder shops, requires amongst other things heating/press fit/stuff us average joes can't do easily...

This all assumes that it is in fact a worn intake valve causing you extra leaking oil!

If you have an auto gas stc. Try not burning avgas and go auto gas only. The green stuff is the coloring from the avgas. Been there done that got a post card. Can not explain why it is green and not blue.

Thanks for the ideas. Seems like I have my work cut out for me. I do have the C-145. I am not really concerned about the green - sounds like the oil from the valve guide is running down the intake and picking up all the residual blue dye from the 100LL - just would like to minimize the fluid loss from my engine.

David, the C145/O300 doesn't have the "spider" that your engine has. It has a carb which uptakes thru the sump and then out each side to a 3-way manifold.
A worn valve guide may still give excellent compressions because that test is done with the valve closed. But an engine with worn guides can have one or more valves in the open position when at rest. The oil will then leak from the rocker-box pas the valve guide/stem and into the cylinder, and down/out the manifold. (Fuel injected engines will then drop the oil onto the pavement as the injection manifold's relief "poppets" open at rest.)