Central Fuel Vent on 1952 C170B

How to keep the Cessna 170 flying and airworthy.

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Jim Collins
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Central Fuel Vent on 1952 C170B

Post by Jim Collins »

Hi All,
I have a simple question to ask but a long story to get to this question.
I just bought my C170B (N2488D) and had to fly it from South Carolina to northern Illinois. Just as I was over the top of the smoky mountains, I noticed that the left tank was still full and the right tank was getting too low for my comfort level. So as I was flying under "Flight Following" for safety sake, I let them know what was happening and they where with me the whole trip to the closest airport on the other side of the mountains. Everything worked out but during the trip I had to stop for gas twice as often as I had planned for.
I originally thought that my fuel selector valve was not working but have since confirmed it is okay as long as the gas caps are removed. It seams the left tank was not being vented at all. First, the left vented gas cap was not working. After taking it apart, I found it plugged with thread locker around an area of the central screw where it was supposed to be able to breath. I reassembled it correctly and now it works fine (permits air to go in but valves off in the other direction).
I then flew it again and found that the right side had used 6 gallons and the left side only 1 gallon. So its now better but still not fixed. I then looked at the goose neck vent and found it vents the positive ram air pressure to the right tank but not the left. It is plugged or something on the left side as confirmed by trying to blow into it and looking/listening to the top of the tank . So the right tank has positive pressure above the fuel and the left has a slight negative pressure from the fuel cap.
So now my question. Does anybody have a picture or mechanical drawing of the goose neck vent and how it plumbs to the tanks so I can know in advance what I have to do to fix it? Or can someone tell me what they did to work on or fix their's? I have tried looking on the this and other web sites but have not found anything helpful.
Thanks
Jim Collins
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Ryan Smith
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Re: Central Fuel Vent on 1952 C170B

Post by Ryan Smith »

Jim Collins wrote:Hi All,
I have a simple question to ask but a long story to get to this question.
I just bought my C170B (N2488D) and had to fly it from South Carolina to northern Illinois. Just as I was over the top of the smoky mountains, I noticed that the left tank was still full and the right tank was getting too low for my comfort level. So as I was flying under "Flight Following" for safety sake, I let them know what was happening and they where with me the whole trip to the closest airport on the other side of the mountains. Everything worked out but during the trip I had to stop for gas twice as often as I had planned for.
I originally thought that my fuel selector valve was not working but have since confirmed it is okay as long as the gas caps are removed. It seams the left tank was not being vented at all. First, the left vented gas cap was not working. After taking it apart, I found it plugged with thread locker around an area of the central screw where it was supposed to be able to breath. I reassembled it correctly and now it works fine (permits air to go in but valves off in the other direction).
I then flew it again and found that the right side had used 6 gallons and the left side only 1 gallon. So its now better but still not fixed. I then looked at the goose neck vent and found it vents the positive ram air pressure to the right tank but not the left. It is plugged or something on the left side as confirmed by trying to blow into it and looking/listening to the top of the tank . So the right tank has positive pressure above the fuel and the left has a slight negative pressure from the fuel cap.
So now my question. Does anybody have a picture or mechanical drawing of the goose neck vent and how it plumbs to the tanks so I can know in advance what I have to do to fix it? Or can someone tell me what they did to work on or fix their's? I have tried looking on the this and other web sites but have not found anything helpful.
Thanks
Jim Collins
Welcome, Jim!

Glad John’s airplane found a home. Do you have a copy of the IPC? If not, go to support.cessna.com and register for an account. Textron has made all Beech and Cessna IPCs available as a digital download for free. That may get you where you need to be.

I do have uneven tank draw, but mostly in cruise above 5,000 feet. The airplane is supposed to be placarded for single tank operation above that altitude, but I’ve seen it lower with mine. It seems to be a relatively common occurrence with these airplanes. I have not seen any need to tear anything apart on mine, but it’s been in the family as long as I have.

Best of luck to you.
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Bruce Fenstermacher
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Re: Central Fuel Vent on 1952 C170B

Post by Bruce Fenstermacher »

It's simple Jim. You need to get access to an IPC so you can look at the illustrated drawings.
Screen Shot 2018-01-28 at 8.50.06 PM.png
The gooseneck Ts. Rubber fuel hose and clamps connect it to metal tubing that runs to the tank where it is connected to the tank nipple with more rubber fuel line tube.

You need to remove and pull you headliner back just a bit to get to it. This metal fuel line is a real SOB to get out. And that is a SOB with the headliner completely removed. You need to cut off the fuel line from both ends or alternately get the tube to rotate and push the tube all the way onto the metal tube. The tube, at least mine are so tight between the tank and the goose neck that this it the only way to move it out of the way of either the tank nipple or the goose neck. Quite frankly you may want to remove your headliner back as far as a foot or two.
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
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Jim Collins
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Re: Central Fuel Vent on 1952 C170B

Post by Jim Collins »

Thanks Ryan & Bruce, very helpful

By the way, what does IPC stand for?
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MoonlightVFR
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Re: Central Fuel Vent on 1952 C170B

Post by MoonlightVFR »

IPC is Illustrated Parts Catalog - purchase a paper copy or just do online free.

You probably have a stuck insect in breather tube.

Consider sucking it out w plastic tubing taped to a vacuum cleaner. Fuel tank should not be full, cap off, and use just partial pulling
pressure - incorporate a lint trap for washing machines. You need to capture the evidence. You will feel reassured with evidence in hand.

Removing the headliner and cutting good tubing could be very expensive shop time and high possibility
of permanent damage to headliner.
gradyb, '54 B N2890C
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MoonlightVFR
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Re: Central Fuel Vent on 1952 C170B

Post by MoonlightVFR »

I would like to retract my previous post.

It could be very dangerous in the use of drawing fumes in and through a vacuum cleaner. Very bad advise.

There are mechanical hand pumps available to suck the debris from the tube.

Have an effective fire plan in effect. Grounding, etc. Always a minimum of two (2) fresh fire extinguishers
on hand.

Regards
gradyb, '54 B N2890C
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gfeher
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Re: Central Fuel Vent on 1952 C170B

Post by gfeher »

Jim, I replaced the flexible vent connector lines (item 28 in the IPC figure shown) at the gooseneck on my '52 B model in 2016. If you decide that you need to remove and/or replace them, I'm guessing that you'll benefit from the notes I made at the time. I did it without completely removing my headliner. If I remember correctly, I was able to loosen mine back from the windshield area about a foot or so, enough to give me access to the vent lines. As others have mentioned, it's kind of a pain to change the flexible connector lines, as it's tough to get a grip on them and the aluminum lines, and you are in an awkward position. But it's certainly do-able, even for a big guy like me. Here are my notes:

"The gooseneck and rigid aluminum lines are all 3/8” OD and have “bulbs” at the ends. The gap between the gooseneck fitting and the rigid aluminum line at the center on each side is only about 1/16”. Use 3/8” ID MIL-H-5593 hose, such as Aeroquip 306-6 (.375” ID, .594” OD) or Stratoflex 193-6 (.375” ID, .60” OD). Do not use any hose with more reinforcing than Aeroquip 306 or Stratoflex 193, as you won’t get them to flex/expand enough to fit over the bulb ends of the aluminum and vent tubes. Replace all of the clamps (use AeroSeal 200-06H). The two center hoses at the gooseneck vent are each about 2 ¼” long. But measure the hoses being replaced before removing them. Cut away the hose on one side. This allows the rigid aluminum line on that side to move just a bit. Then replace the center hose by sliding it onto the rigid line then back onto the gooseneck fitting and tighten the clamps (not as easy as it sounds). Repeat for the other side. You WILL need to use engine oil or WD-40 (either preferred) or dish soap to lubricate the aluminum lines and insides of the hoses before sliding on the new hoses. Given the tightness of the hose and the space you are working in, you will have some difficulty getting the hose over the bulb at each tube end. But once the hose end is expanded over the bulb, you can then work the hose on further a little more easily a little at a time."

The measurements were taken from my plane when I was doing the work, but I'm guessing that they are typical for at least my model year. Hope this helps.

By the way, I doubt you will ever get even draining from both tanks. Like many others, mine drains faster from the left tank. But as both tanks get lower, it begins to even out. It may be a quirk of the design, but I'm not sure. (Maybe I make more left turns? :))
Gene Feher
Argyle (1C3), NY
'52 170B N2315D s/n 20467 C-145-2
Experimental J3 Cub Copy N7GW O-200
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Jim Collins
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Re: Central Fuel Vent on 1952 C170B

Post by Jim Collins »

Thanks Gene,
Everybody on this site is very helpful. I ordered some of the hoses you recommended from Aircraft Spruce and it said that the hoses where for air & vacuum and did not mention being fuel prof. I just wanted to make sure your hoses did not turn into a sticky mess over time and that the materials really are okay for fuel and the notes from Aircraft Spruce are just a type-O
Thanks again
Jim Collins
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gfeher
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Re: Central Fuel Vent on 1952 C170B

Post by gfeher »

Jim, no mine did not turn to a sticky mess. They've worked fine. When I changed my hoses, I originally bought the hose recommended for fuel lines. I don't remember whether it was Aeroquip or Stratoflex. But it was one of them. I struggled for hours trying to get it on. I couldn't get it close to expanding enough to fit over the bulb ends of the aluminum tubes. So I went to an IA friend on my field and said "what am I doing wrong?" He has a ton of experience working on single engine Cessnas and he immediately spotted the problem. He replied, "you'll never get that on." And handed me a short length of one of the hoses I mentioned in my notes and told me to use that. Problem is the fuel line hose has too much reinforcement to expand over the bulb ends. He said that the hose I mentioned in my notes is regularly used for such vent lines on early Cessnas. That's why I listed it in my notes.
Gene Feher
Argyle (1C3), NY
'52 170B N2315D s/n 20467 C-145-2
Experimental J3 Cub Copy N7GW O-200
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jlwild
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Re: Central Fuel Vent on 1952 C170B

Post by jlwild »

Jim, check out the pictures and slide show format on "fuel tank removal" in the members only section. It will enlighten you on the "T", furl selector, and fuel tank issues I encountered. Before opening anything up, I would also call previous owner to discuss if he did any repairs to the fuel system. As others have said, it's a big job.
Jim Wildharber, Kennesaw, GA
Past President TIC170A (2010-12) and Georgia Area Representative
'55 170B, N3415D, SN:26958, O-300D; People's Choice '06 Kelowna, B.C., Best Modified '07 Galveston, TX, Best Modified '08 Branson, MO.
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GAHorn
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Re: Central Fuel Vent on 1952 C170B

Post by GAHorn »

Hello, Jim!
Sorry to be slow to respond to this but I've been on a trip away from "technology" for a few days.

The situation with high-wing Cessna's appearing to feed from only one tank is actually a WELL KNOWN ISSUE.

In the 170 A and B airplanes the cause is NOT what you think. In actuality... BOTH TANKS are truly feeding your engine (if no defects exist in the ordinary sense.)

There is an AD note which requires a vented fuel cap on the RIGHT fuel tank for these airplanes. (Most folks have vented caps on BOTH nowadays...as that is all Cessna will sell you for this airplane.) The good method to determine if your left or right tank is venting properly is to open a cap on a tank which is NOT full of fuel, and apply a LIGHT suction or pressure to the "gooseneck" vent and LISTEN for the sound of moving air at the open cap. Another method is to attach a hose to the goosneck and a funnel at the other end of the hose to create a "speaking tube"... and have someone speak into the funnel (or have a portable radio play into it) and listen at the open fuel cap for the sounds.
I will bet a box of donuts that your vent is working properly. (I have a very fine stainless-steel screen inserted into my gooseneck to keep critters out. A perfectly-fitting screen is already found in the bottom of the snorkel of an old can of Alcor-TCP fuel treatment.)

The common misconception that our 170's are subject to a requirement for SINGLE-TANK OPERATION ABOVE 5K feet is not correct. That requirement only applies to a particular serial number-range of Cessna 172 SKYHAWKS... not the Cessna 170 models. (It was due to a "percolation" of air bubbles in fuel supply lines which contributed to an engine "miss" at cruise in a design-aberration not applicable to the 170 airplanes.)

The reason your left fuel tank appears to not be feeding the engine during operation on BOTH is because the right-tank is replenishing the left-tank via the overhead vent-line which connects both tanks to the gooseneck vent. In reality... BOTH TANKS ARE SUPPLYING FUEL to the engine equally...but the left tank is also "sucking" fuel from the right tank and being re-filled.... until the head-pressure differences between the two tanks reaches a level sufficient to overcome and "break" the siphon which occurs in that overhead vent line. This is a very common event in these airplanes and has been reported and commented upon many times.

If it bothers you... then after takeoff and a hour's flight....switch to the left tank for an hour then switch back to both for the rest of the flight.

BUT REMEMBER TO ALWAYS SELECT BOTH FOR TAKEOFF AND LANDING.

Hope this helps.


From nn older forum discussion regarding the "5K' operating instruction, I had talked directly with Cessna on this matter:

The ANSWER to the question is: Single tank operation above 5,000 feet only applied to the 172, per AD 72-07-02. (72-07-02; Title: CESSNA Models 172, 172A, 172B, 172C, 172D, 172E, 172F, 172G, 172H, 172I, 172K, )

Some 172 owners reported engine surging above 5K feet and Cessna went to great lengths to duplicate the problem but never could. They even installed clear fuel lines in a vain attempt to observe the vapor bubbles which never appeared. The FAA was certain there was a fuel head-pressure problem, so Cessna gave up fighting it and accepted this AD note. It only applies to 172's. It presumes that a clogged fuel vent line on one tank might reduce fuel head pressure sufficiently to cause formation of vapor bubbles which in turn might cause engine surging. Switching to one tank should either isolate or identify the offending fuel tank. Selecting the opposite tank would cure the problem. (No one seems to have noticed that if a tank's vent is fleetwide problematical, that selecting that tank would worsen the problem fleetwide in some consistently identifiable manner and therefore confirm the need for, or uselessness of the subject AD. Since no one has subsequently complained, the FAA feels they have correctly solved the non-existant problem, and the AD remains in effect.)
========
and
========
I just got off the phone with Cessna Technical Rep. Tim Fischer who had consulted with the retired Cessna Rep. responsible for developing this procedure that responds to the AD 72-07-02. Here's their answer:
The airplanes that experienced problems were later model Lycoming-powered 172's. Although with an altered fuel system which included short vent lines connecting the fuel delivery pipes to the fuel vent pipes, the problem continued. Although the factory was unable to duplicate all the symptoms reported by some operators, they did develop this procedure which eliminated all further complaints. (The Lycoming engine's greater fuel consumption may have contributed to a lowered head pressure in a system primarily designed for the C145/O300 engine.) Although none of the Continental-powered airplanes suffered from the problem, Cessna thought it conservative to include them in the AD note. (After carefully listening to the development of the conversation, I suspect it was to avoid casting dispersion upon their newly selected engines of choice, since Continentals would no longer be offered in the 172. In other words, they were not going to go back to the Continental as they'd bought over 4,000 Lycomings and had them in stock, so in order to not make it look like they'd selected a troublesome engine, they were anxious to make it apply to all previous aircraft. My own suspicion.-gh)
Even though the straight 1956 model 172 has exactly the same fuel system as the 170B none of the taildraggers ever had any such problems. (Nor in fact did any of the Continental 172's.) Proving this point to the FAA would cost Cessna a lot of time and money on airplanes no longer manufactured. Cessna took the easy way out with the FAA.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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Jim Collins
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Re: Central Fuel Vent on 1952 C170B

Post by Jim Collins »

Gahorn,
As I have commented on before, everyone on this site has been very helpful. Thank you.
Without a doubt, no question about it, 100%, I had a situation where the left tank had no way to vent at all. I could not move any air (in or out) of the gas cap. Found it plugged with thread locker. I then cleaned it out and put it back together with thread locker only where it needs to be. Now I can blow air into the cap but not suck air out which is I think how it's supposed to work. I then used an air compressor set to just 2psi (for safety) and connected it to the goose neck with half of the fuel removed from both tanks. Air could clearly be heard going into the right tank but dead silence in the left tank. So it seems to me that the path from the goose neck to the tank must be plugged with something. So that is why I have been asking how to do the job of fixing that vent.
Thanks again, I am learning a lot.
Jim Collins
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GAHorn
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Re: Central Fuel Vent on 1952 C170B

Post by GAHorn »

I owe you a box of donuts then. :wink:

I used to own a 206 and that airplane, being fuel injected, did not have the capability of operating on "both"... it was either right or left. One day I noticed that during flight that the right tank gauge did not "drop" after an hour's flight as it usually did, and after looking into it... (after opening the fuel cap and discovering the fuel bladder was slightly collapsed)... I disconnected the vent line and found a beautiful CIGAR.... a really nicely rolled-up cigar of green leaves that some insect had created and stuffed into that line... and it was nowhere near the vent-opening...it was WAAY inside almost all the way to the tank itself! 8O

So.. it IS possible to have such things occur and I presume also with the 170 airplane...and is why I have a fine-mesh screen installed on my gooseneck.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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170C
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Re: Central Fuel Vent on 1952 C170B

Post by 170C »

George, do you use TCP? Got an extra screen you would consider sending my way?
OLE POKEY
170C
Director:
2012-2018
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ghostflyer
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Re: Central Fuel Vent on 1952 C170B

Post by ghostflyer »

If you need a screen and have a old carburettor, inside there is a mesh finger filter and that fits exactly over the forward facing vent on the roof.
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