The International Cessna^® 170 Association

Hello all!

I am a new owner of a beautiful 1951 170A. I'm getting some of the squawks worked out while flying her and making her "mine".

In this process, when I went to pull her out the other day, I saw a puddle of...something....on the hangar floor underneath what appears to be a breather hose. It's liquid, but is slightly viscous. It is tan-ish. It looks like coffee with a bunch of milk in it. It will smear, as opposed to running. See picture below
The first puddle is from a week ago, the second is one day old
https://ibb.co/7YrM7PT

The puddles were directly below this portion of the cowling. I've circled the hose I suspect its coming from in red
https://ibb.co/JrpPwtr

Any clue what this is? Should I be worried? Should I just put a drain pain down?

Thanks all!

Welcome to the dirty bellies club. My '48 does the same thing, it's just a frothy oil/water mix dripping out of the breather. Nothing to worry about.

I assume you've done a recent compression check? Blow-by can make the frothing worse. The breather on my 250-hour O-300 drips a little clear-ish liquid, mostly water with just a little oil. My 1300-hour one makes that milky coffee-colored froth you mention.

Yep! That’s the crankcase breather, and the frothy creamy-liquid is oil and crankcase vapor that has condensed water vapor in it. (Normal stuff)

The by-product of burning fossil fuel is mostly Carbon monoxide/dioxide and water vapor. That tube routes from the top/forward area of the crankcase and goes over the right-side cylinders, back to the baffle-bulkhead, then down to the lower cowl exit (where you’ve circled.). This conveys crankcase gases overboard whenever the engine runs. Since the thrashing parts inside the engine spews oil mist and vapors, this tube prevents pressure build-up inside the crankcase, and after shut-down whatever is inside the tube condenses and drips out the bottom onto the hangar floor.
It usually looks like dirty, oily, watery foamy sludge... because it is!
And it’s normal to see a whiskey shot glass of it drip after a flight. (Like gasoline and blood, a little bit looks like a lot.)

And old piece of cardboard on the floor will make cleanup easy. (Some of the aerobatic club types run that tube all the way back to the tailwheel to keep it off the belly in-flight, and then when in the hangar they’ll hang a small tin-can from the tube to catch the sludge, but that’s just ridiculous for us real guys. I mean, what the heck will we do with our goggles and scarves?).

By the way, if you look up the tube from where you circled, up inside the exit area of the cowl, about 10-15 inches , you should see a 1/4” hole drilled through the side of that aluminum tube. The purpose of that hole is to provide an alternate exit in the event that water vapor freezes in cold weather and blocking that tube down at that area circled. Should that tube become blocked the internal pressures of the crankcase can cause the crankshaft/propshaft seal behind the prop-flange to “blow” and you’ll begin to see oil droplets hitting your windshield in flight!

Yep. Normal to see sludge after a flight.

Interesting, could be me but It appears to me to be a smaller diameter tube than usual for a breather hose / tube and a somewhat extended length. Good news; from the look of the belly your engine appears to be leaking oil normally

c170b53 wrote:Interesting, could be me but It appears to me to be a smaller diameter tube than usual for a breather hose / tube and a somewhat extended length. Good news; from the look of the belly your engine appears to be leaking oil normally

GOOD CATCH , JIM! (That actually appears to be a battery-box drain.). But the crankcase Vent tube is in the same close area, just above/forward, and not readily apparent in that pic, ... the OP’s attention is in the right spot.

If the battery is producing that stuff it would usually smell like sulfur and is very corrosive. That sort of thing is usually caused by a failed regulator which is overcharging the battery and causing boil-over. (I interpreted the ”Sludge” as oily considering he said it “smeared”, and if it was acid/boil-over it would have eaten the concrete in a week.)

This is the puddle under the crankcase breather on a 475smoh engine after a 1-1/2 hour flight. I keep the oil level at 6qt.

I have seen people over fill the crankcase and it will blow out through the breather but also I would fill the crankcase to the correct fill mark and go and fly it flat out if you had stole it for about 2 hours . Naturally keeping all engine parameters in the green. One pot might have not bedded in and the bores are glazed. While I am a big fan of superior engine products , I feel their piston rings are not as hard as continental or lycoming rings. I also think oil brands and their viscosity also play a part in oil consumption.
So there is a mixed bag of issues that has to be contended with . For a engine that has done 500hrs I would be looking at oil consumption of 1 liter every 9 hours. They can burn a lot more and still be within tolerance . There are many situations that can cause oil blow by but blow by must happen or you can blow seals .

Man, you all are awesome. Thanks for the replies.

I sincerely hope it's not battery, as it hasn't eaten into anything. It does seem to be mostly water. I will check where the breather goes and for that alternate drain hole next time I'm at the hangar.

I'll reply with follow up, thanks again guys!

Hope this helps you getting the new plane all lined out like you like it. You have purchased a true classic airplane.

It also looked like a small spot of 100LL on the floor under your gascolator. It might need new gaskets if that is what it is.

As you have seen, there are a lot of resources available in this organization. There are many more resources available to members that non-members cannot access. The membership fee is well worth the cost and helps keep the info available for future use.

I may be a little late to the party, but I am experiencing a similar issue. After about an hour of flying I have a similarly sized puddle of oil coming out of the breather tube coming off the case. I have about 1300 hours on the engine and about 50 to 60 hours on 6 new Millennium Cylinders. I have been keeping the oil at about 7 quarts and add a quart every 3ish hours. Is this normal? Compressions are all in the high 70's. Am I over filling it? The belly isn't covered in oil either.

Thanks!

Max

When I let my oil level drop to below 6 qts, virtually all oil consumption stops.

I keep ours at 6 - 6 1/2 for consumption. Oil sludge out the breather can happen when the breather tube from the front has a downward slope to the rear. If the slope is upward to the rear the oil will drop out and drain back into the engine.

John

Good to know! I will let it get down to 6 and maybe it will stop puking!

Thanks again for all the help!

n3833v wrote:I keep ours at 6 - 6 1/2 for consumption. Oil sludge out the breather can happen when the breather tube from the front has a downward slope to the rear. If the slope is upward to the rear the oil will drop out and drain back into the engine.

John

John, I hear what you are saying but if oil drops out and runs back into the engine, I think any water vapor in the vent could also drop out and run back to the engine. I would rather keep a drain pan under the engine or wipe up the floor than have water run back into the engine.

I have also found if I remove the engine oil filler cap immediately after each flight, there is steam coming out of the crankcase and less sludge drips out of the breather. I leave the cap off until the next flight and the cowl on that side unlatched to remind me the cap is off. We all check the oil level before each flight, right? So leaving the cap off should never cause a problem. This only works if the plane is in a hangar, if outside he cowl can’t be left unlatched and there would be more risk of dust contamination and/or forgetting to put the cap back on.