The International Cessna^® 170 Association

Well it finally happened. The airport was resurfacing the taxis to the hangers so we had to leave our planes on the ramp if we had any desire to gain access to them for flying. We had rain this fall and everything was going good until last weekend. Saturday I went out to the plane and during my pre-flight I noticed water in the gas . I sumped them a few times and got clean gas from both wings. There was no water in the gascolator. I did a 15 minute flight to another airport to pick up a friend and decided to sump the tanks - more water. Every stop we made I could get more water from the sumps. We flew about 1.7 hours total that day and the engine ran ok and there is no water making its way to the gascolator. How worried should I be? Is there a "trick" to getting all the water out or will it eventually work it's way to the sumps without any problems. I realize these are open ended questions as there is no real or easy way to determine how much water is in the tanks. I was able to put it back in the hanger Saturday. Any thoughts or ideas? I just don't want to have any problems - I cause enough stress as it is

Paul

Paul,

'98C's been out on the ramp for almost a year now (very soon to change, I hope), and I did get some water last winter (our wet season). I try to sump the tanks first thing on arrival at the airport, then give the wings a good shake right after removing the tie-down chains to move any trapped water and give it a chance to settle during the preflight, then sump again right before loading up. During the rainy season, I might have to do this several times to get a clean sample.

Oddly enough, I've never seen any water in the gascolator, but I did have a leaky float valve in the carb on the way home from Galveston (on the ramp through several rain showers), and found a couple specks of dirt and a dime-sized dollop of water when I drained the bowl.

Miles

The first thought is that rainwater gained access thru the fuel caps, but that may not be what actually happened.
While your airplane sat outside it may have experienced much larger temperature excursions than normal due to direct exposure to sun/nighttime changes. This causes quite an increase in the exchange of atmosphere in/out of your fuel vent system, such atmosphere containing moisture, of course. As it cooled down the moisture condenses on the inside surfaces of your tanks. Eventually it runs down into the fuel.
You find this on preflight draining of wing sumps. None has thus far made it to the gascolator because the plumbing leaves the wing tanks at the inboard mid-point, which is up-hill from the 3-point attitude.
Even if you drained all the water from the bottom of the fuel, there very likely is more condensation still clinging to the upper surfaces of the interior tank walls (the area of ullage) which did not wash down into the fuel until disturbed by flight. (I know. I know. You are especially talented and gifted and hardly caused a ripple in the fuel during your handling of the aircraft, but the braking action during roll-out, and the turn-off from the runway.... )
So you found some more after the flight.

This can happen after any flight, as well. If a warm airplane goes to cool altitude...or if it stays up there in a temp-inversion and descends thru cool air...it can pick up a load of water.

The gascolator is intended to catch these small amounts prior to it getting to the carburetor. That's why it's important to drain the gasocolator after EACH flight and BEFORE each flight...so as to remove any fuel-borne water that may have reached that gascolator, and to provide room for any additional that may coalesce during subsequent flight. (And it's another reason to avoid fuel containing alchohol which will precipitate water out of the fuel and may overwhelm a gascolator.)

Paul

I wish I could afford a hanger but I'd have to sell the 170 to do so, so there isn't much point. So my plane sits outside all the time.

Over the years until recently I used nearly 100% MOGAS and so was always on the lookout for water from that source as well as those already mentioned above.

Occasionally I'd find some small amounts say an inch or less or maybe as much as half a tube in the fuel sump tube and drain it as you have. I personally would not worry about these small amounts no matter how often you find them. That is exactly why the drains are there and exactly why you should drain them at least before every flight.

If you found say 10 oz of water I'd start to wonder how it was getting in the tank. That is just to much under normal circumstances of regular weekly draining before flights.

In my case it started to happen only in one tank. Since I put the same fuel in each tank and both tanks are in exactly the same environment it was pretty easy to conclude that I had a leak allowing rain water in. Though they looked good the gaskets sealing the tank filler and the moat surrounding it were shot. New gaskets and no more trouble.

It sounds like your are finding a normal amount of water and if it doesn't get any worse I wouldn't worry about it.

I know. I know. You are especially talented and gifted and hardly caused a ripple in the fuel during your handling of the aircraft, but the braking action during roll-out, and the turn-off from the runway.... )

You obviously have me confused with someone else . My fuel ripples and shakes in fear even as I approach the plane from a distance! All kidding aside - thanks for everyone's input. I've been only flying for a couple of years now and ownership for about the same time and this is the first time with water. This is an awesome organization and I feel that this was the best investment made.

I wish I could afford a hanger but I'd have to sell the 170 to do so, so there isn't much point

We are currently renting a hanger but are starting construction this fall on a 48 x 52 heated hanger with a bathroom. Will be nice to have a warm spot to "putz" on the plane when the winter winds are blowing and just too lousy to go flying.

Paul

gahorn wrote:... Even if you drained all the water from the bottom of the fuel, there very likely is more condensation still clinging to the upper surfaces of the interior tank walls (the area of ullage) which did not wash down into the fuel until disturbed by flight.

That's why it's a good idea to rock the wings early in the preflight, well before the final sump check. If tanks are full, or nearly so, the fuel will wash the water from the ceiling of the tank. Doing this early in the preflight will give that water a chance to settle to the sumps.

gahorn wrote:... (And it's another reason to avoid fuel containing alchohol which will precipitate water out of the fuel and may overwhelm a gascolator.)

Do you have this backwards, George? Water is not miscible in fuel. Alcohol is miscible in in both fuel and water, but has a preference for water. Adding water to fuel containing alcohol will precipitate the alcohol out of the fuel. IOW, you test for alcohol by adding water, not the other way around.

Miles

cessna170bdriver wrote:...

gahorn wrote:... (And it's another reason to avoid fuel containing alchohol which will precipitate water out of the fuel and may overwhelm a gascolator.)

Do you have this backwards, George? Water is not miscible in fuel. Alcohol is miscible in in both fuel and water, but has a preference for water. Adding water to fuel containing alcohol will precipitate the alcohol out of the fuel. IOW, you test for alcohol by adding water, not the other way around.

Miles

No, I don't have it backwards...but I may have required a mental leap in order to follow my logic!
Alcohol will indeed attract water in fuel, and ...after a period of time at cool altitudes, it may allow the water/alcohol to precipitate out of the fuel and overwhelm a gascolator inflight. Bad news when that happens.
Moral: no alcohol should be allowed in fuel, regardless of FAA approvals for anti-icing purposes. (See the Warning note on page one of the TCDS.)

I agree that alcohol in our airplanes is (currently) a very bad idea, but I don't think that "precipitation of water out of the fuel" is very high on the list of reasons why. Alcohol's incompatibility with "certified" fuel system components, and higher specific fuel consumption come more immeditately to mind.

Speaking of mental leaps, I've never been able to make the one of figuring out why my car's 12-gallon gas tank isn't overflowing with water and alcohol after pumping approximately 10,000 gallons of California-approved mogas into it, and that car enduring 50-degree temperature changes and 2000-foot elevation changes twice a day for 11 years.

Miles

Do you suppose the fact that it's gas tank sits only a few inches above a warm paved surface and that it does not experience large altitude changes associated with high rates of depletion (intro of larger amounts of moist air over the period) might have something to do with it?

I know you already know...but the comparison is not apples/apples. Autos typical fuel system introduces fuel through a plumbing system which brings already-warmed fuel (usually already pressurized by in-tank pumps) into and over high engine compartment temps, at (usually) lower consumption rates and under greater pressures, most frequently to manifold co-located fuel injection systems. Even older carbureted systems experience greater exposure to vapor-lock issues from elevated fuel temps than to cooled fuel under gravity head pressures. Our airplane's have gravity fed systems, coming from tanks located well away from heat sources which lead to the gascolator, and plumbing which provides limited exposure to engine heat in updraft carburetor systems. Even so, the heat which is available is applied at points downstream of the water-collection point (gascolator.)

I agree, the corrosive and other damaging effects of alcohol in fuels is of primary importance, but I've personally experienced a gascolator which was overwhelmed by water/alcohol ...in an A&P's C-182! He used "gasahol" religiously until it quit on us during initial climb at night!
The airplane was properly pre-flighted, sumps drained (while still in the hangar), then it was pulled out into the cool night air where it stood for the next half-hour while he finished work and closed up the doors on multiple corporate hangars. The early evening hours had just experienced a cool-down and we were going flying ... or thought we were...when the engine sputtered while about 100' above Rwy 13L at DAL.
He used to be an autofuel junkie, but no more. (Fair enough, that airplane also had rubber bladders which may have had wrinkles which may have trapped some water/alcohol in puddles that escaped the sump-draining activities. But regardless, it was the ethanol-laced fuel which attracted the moisture which was subsequently dropped out of solution and overwhelmed the system.)

From Ben Visser, retired Shell fuels/oils expert who writes for General Aviation News: "The water reaction tests in D-910 (AvGas specification) are also important, to ensure that all of the water in your fuel tanks can be sumped. Here again, all of the non-oxygenated (non-ethanol) auto fuels that I have tested passed this spec. Conversely, all of the alcohol-containing fuels failed the test."

From one of the most vocal proponent of autogas STC's, the EAA:
"Alcohol in autogas when used in aircraft has caused numerous problems such as fuel leaks and fires due to rapid deterioration and swelling of rubber gaskets and seals. Fuel tank quantity floats made of cork and/or composite materials are attacked by the alcohol in fuel and allow particles to float in the fuel, clogging fuel screens, plugging carburetors, etc.
Sloshing compound used in many fuel tanks to seal leaks also reacts with
the alcohol, causing fuel leaks and fuel system contamination. ... Swollen float needle tips cause alean mixture and eventual engine
damage. Cessna aircraft with rubbertipped fuel strainer plungers are also
damaged by the use of autogas with alcohol and frequently leak after a short time of use with an autogas/alcohol mix. Most recently a “malfunction” appeared in the FAA alerts describing a
Piper aircraft that caught fire in flight due to a leaking fuel strainer gasket that was swollen by the use of alcohol mixed with autogas. The pilot was able to turn off the fuel to stop the fire and save himself but he was forced into becoming a glider pilot. Any rubber part such as fuel lines,
fuel cells, and 0-rings in fuel selectors are subject to damage from alcohol
mixed in the fuel." (Bold emphasis is mine.)

Besides the standard wing tank sumps and gascolator sump, my bird also has a sump installed in the belly, roughly beneath the fuel selector. I bought the plane this way, but the rationale I learned for it was that this lets you sump the lowest point in the system, when the plane is on the ramp. It is downstream of the fuel cut-off, because I have to have the fuel cut-off knob in to draw fuel at this belly sump. I sump it before each flight, just as I do with the other sumps, but I don't think I've ever gotten significant water there, though I sometimes do in one or the other wing tanks, if it's been outside for a while with less than the recommended full-fuel.

Also, does anyone know if the wing tank sumps are plumbed to the LOWEST point in the wing tanks, when in a 3-pt attitude, or are they slightly higher, leaving an un-sumpable quantity of water in that very aft-most portion of the tank?

We are now experiencing freezing temps and I had trouble recently pushing the drain-cock to sump one of the wing tanks. I surmised that this is because there was a little water in there that had turned to ice and obstructed the movement of the drain-cock, but I'm not really sure.

Thanks,

Denalipilot

I think you may have surmised your sump situation succinctly, Simon.
The sump drain is almost at the lowest point in the 3-pt attitude. Manufacturing necessitates that it be placed inboard/forward of the tank aft wall/inboard bulkhead, simply in order to make room for the device. The area that is downwards from it is almost negligible, and is unavoidable. It is unlikely to cause significant problem, but it is possible for water in the sump to freeze and lock the drain valve.
You might consider a warm-air heater (not a hair dryer.)

Bruce,

I think I might have the same issue. How difficult was the gasket replacement job? Who did you get the gaskets from?

Thanks,

Forrest

Forrest

The job of removing the tanks can be a pain because you must remove all the screws holding the tank cover on. This can take for ever and try your patience. You will never know how hard it will be until you start. Mine came right out. What was more difficult was repairing damaged nut plates someone had left from the last time it was done.

After the tank cover is off you will probably want to remove the tank and clean the bay. This is a good time to remove your tank gauge and inspect the cork and workings. Then the tank hold down strap rubber will probably be shot. And on and on.

So the long and short of it is if it comes right a part and you find no other repairs to accomplish then it's a nice afternoon job. Otherwise it will take longer.

You can order the gaskets but I seem to remember at least one of the three gaskets costing about $25 and the other two about $20 or about $70 for just the three gaskets you need just for the top.

I cut my own gaskets out of impregnated cork material available in many places. Total cost about $20 with cork material left over. I took the time to draw templates of all the gaskets you will need including the gas gauge and can send them to members in PDF form. You can print them from your computer and use them to cut your own gaskets before starting the project. Then you can decide if you want to buy the gaskets before you get into it.

I've actually planned to write a "How To" article about cutting your own gaskets but haven't gotten to it yet. And I'm building a library of gasket templates as I get them for the association to share.

Thanks for the info Bruce.

Forrest