what is this??

[Canadian]

See photo. I noticed this at Marathon on my way back from Thunder Bay to Ottawa, photo taken on arrival at Ottawa. It's a fine powdery residue that easily wipes off with a finger.

Relevant facts:
* Engine is Continental O-300D in a C170
* This is after 14 hours of flying over two days, no rain or anything to wash it off.
* All engine indications were normal and healthy at all times, runups perfect, no issues whatsoever (although I've always felt power is not quite as good as it should be, climb is anemic when loaded)
* This trip was at higher altitudes than usual (5500-7500ft), steady cruise, lean to stumble, enrichen to smooth, as normally prescribed for this engine
* My normal pattern of flying is an hour or so every few days, rarely over 4000ft, and usually there would be rain between flights.
* My mechanic recently noted traces of a similar residue underneath the airplane on the right side, where rain would not wash anything away -- he thought this might be evidence of a problem with cylinders on that side only, since there was nothing on the left. Right now (hard to photograph) there is similar (but less apparent) residue underneath the airplane from the right side exhaust - slipstream keeps exhaust from the right side under the plane, while the left side flows as you can easily see here.
* [Probably irrelevant, but another departure from normal] I did an oil change immediately before this trip, and put in 7 quarts which brought the level up over 8 -- too much, but should just blow out the breather (which it did, I have a belly cleaning job to do)

I'm thinking it may have been doing this all along, but with my usual flying, there would be no noticeable buildup on any given flight, that would be washed away between flights by any rain. I've often noticed some rain drip streaking along the side there, but never thought anything of it until now.

I'm sending this photo to my mechanic, will address it with him on Monday, but I'm wondering if any of the experts here can diagnose this...

[Lopez]

Looks like normal exhaust residue to me. When you lean em out right we get that all the time up here in Denver.

[Canadian]

Really? That would be a relief. Especially if it means I am "leaning it out right."

[Bruce Fenstermacher]

Looks normal to me other than there is a lot of it. Perhaps the most I've seen on a 170. I've had that much on my Cub however. Wipe it of and forget it.

[hilltop170]

Looks like to me you have a good, clean running, healthy engine. That residue is mostly from the gas you're burning. I would not leave it there very long as it could turn corrosive over time especially on that bare aluminum.

The most probable reason it shows up so much on your airplane is the exhaust stack has been cut off backwards to what Cessna originally did. Cessna cut off the exhaust stacks essentially parallel to the cowling which put the angle to the front, not the back. That blows the exhaust down and forward allowing it to clear the fuselage. Your's allows the exhaust to hug the fuselage. Check inside the cowling also, I bet there is residue in there as well. No big deal, just requires more cleaning.

Lengthen the exhaust stack and cut the angle parallel with the cowl and it will go away.

[lowNslow]

I'll echo what Richard said about your tailpipes. When I bought my airplane years ago I had the same problem. Installing them correctly greatly improved the problem (I still get some residue on the cowling, but not near as much). Your picture also illustrates a point George brought up in another thread about exhaust entering the cabin thru the gear attach point opening. Make sure the rubber seals (PN 0511125) under the fillets are in good shape.

[Canadian]

Well, I'll be darned.

I just looked an any pics I could find of other 170s, and as a couple have said the pipes are cut either more-er-less level, or slanting the other way!

I can see that would make a difference. Well, that goes on the list to look at on next year's annual, as well as inspecting those rubber seals (good point, when you see the flow pattern like this). In the meantime, I'll wipe it clean after each flight. As I said, normally there's not enough to notice, and what there is is rinsed away when it rains. This also explains the residue under the cowl on the right side, where it would not get rinsed away by rain, and there is a bit of pitting happening.

Thanks, everyone.

[Mike Smith]

I have those same stains/deposits on my cowling. I usually wipe them off every month and every few months I'll wax that area to make it easy to wipe the exhaust stains off the cowling. I fly 2.5 hours per week at 5500-6500', and lean the engine like you described. I very seldom fly in the rain (this time of year ) so I see this stuff from April to November, and less so from December to March. My exhaust stacks are angled differently from yours and I don't have quite as much exhaust residue as in your picture. Mine usually only extends 1/3 to 1/2 of the way back to the rear of the cowling, maybe due to the angle of the exhaust stack.

Hope this helps,

[voorheesh]

This is exactly what I have on my 170 A. Is George's WD-40 brew a good way of cleaning this up? Are there any other suggestions for cleaning stains like this on bare aluminum? BTW, could you give the WD-40 - H2O ratio once again?
Thanks

[hilltop170]

I remember George saying one cup WD-40 per gallon of water but I'm confident if that's not right we'll hear about it.

I use a product from WashWaxAll called Belly Wash. It is made for airplanes and is water soluable, not corrosive, and melts exhaust stains. http://www.washwax.com/

Once the area is clean, another product called Rejex from the CorrosionX folks is specifically made to keep exhaust stains easy to remove. http://www.corrosionx.com/

[flyguy]

I just looked an any pics I could find of other 170s, and as a couple have said the pipes are cut either more-er-less level, or slanting the other way!

You can look at mucho photos of Cessnas of all the 100 series and see exhaust stacks angled all 4 ways as well as straight cut, You will see them protruding 2 inches up to 6 inches below the cowl. So what is the answer to the question. Some will say "forward slant" will help "blow" the exhaust away. Others will say aft slant will help the slipstream scavenge the exhaust. One real solution ist he Bartone type exhaust pipes.

Here is my observation. Having been 93Ds mascot since 1972. She never put much stain on the belly with 80 octane. When we began to be force-fed 100 LL, the "blue" residue began to show up, especially on extended flights with the accepted leaning techniques. My stacks (see photo) protrude about 5 or 6 inches and are cut with the slant facing aft. That probably is OEM because they have never been changed in the time of my ownership.

The one glaring difference I see on your photo is the "sea plane" lip that obviously changes the flow around the forward and side area between the exhaust and the lip. If you need the "lip" you are going to need longer pipes and possibly a different angle cut. And as "lowandslow alerted you: "Make sure that exhaust can't get into the cabin"!

Getting rid of the "white" residue is easy. Just wash it off like you would do in a regular way. The "blue" stain is a different matter. It takes more advanced treatment. I used to use "SimiChrome" - - a non abrasive product, sold in bike shops in the 60s, to take the "blue" off chrome exhaust pipes. On a polished belly, it took a lot of work because the discoloration went almost all the way to the tail. After several years I gave up on that stuff and used my cyclo polisher with light polishing compound. After 20 yeas of polishing I sorta gave that up too! ! Just before the Galveston convention. she got a good polish and new paint and was nearly ready to fly there. Some weather and other stuff got in the way and delayed those plans. Now due to other problems she is still a "hangar queen" .

[W.J.Langholz]

I believe it's 1 cup wd per gallon h2o, that's what i used anyway last week-end and it worked ....I did use warm water in a two gal hand spayer and made sure it mixed up good. It did good on the bugs too!!!! I also used warm water for the rinse, shined like a babies behind when I got done

Gar aren't you concerned with undo stress on the muffler with the longer pipes? I had gone down to exhaust pros and picked up some nice 4 inch chome extensions and when I put them on it made my plane look like a walrus that just got back from the dentist I was also concerned about the muffler so I never did use them. There over in the corner with the rest of the junk.
I don't get as much stain when I burn 87 and what's there is lighter in color also.


W.

[Bruce Fenstermacher]

Gar you've got 275 days till the Benton Harbor.St Joseph, MI Convention. Thats 6,600 hours or 396,000 minutes or 23,760,000 seconds. Should be plenty of time to get the "other problems" and "stuff" taken care off and have "the Queen" at the convention.

[Farnold]

Speaking of WD-40 - is George's concoction ok for the windshield?
I have used it on bikes and it does make them shine great.
Leery of anything but water on my windshield.

[GAHorn]

WD40/water will not hurt the windshield. (Ever notice that some windshield mfr's actually recommend kerosene as a bug-cleaner?)

It is a great tar, bug, and belly-cleaner when used full-strength, also.

The white stain is lead oxide and lead bromide. Alcor TCP or Decalin (contains TCP) will greatly reduce this residue and also help avoid spark plug and valve fouling.
Alcor TCP: http://www.aircraftspruce.com/catalog/a ... cortcp.php

Decalin (TCP): http://www.aircraftspruce.com/catalog/a ... ecalin.php