C177 Cardinal Fuel Vents

luvflyin

luvflyin

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Luvflyin
A 71 C177RG I'm scheduled to fly tomorrow has a fuel vent problem. The left vent seems plugged. I blow into it and it is blocked. Can't suck either. It had just returned from a flight and both tanks have close to the same amount of gas in them. On Cardinals the vents which are at the wing tips vent the opposite tank. Something seems wrong here. Any Cardinal experts out there?
 
funny but I flew a 74 for a number of years and had the same experience with the same side. had the mech. check it out and said it was fine. still seemed like it was blocked but never had a problem...
 
Are you sure it’s blocked if the tanks are being used evenly? Or do you think the filler cap vents are being used? When you suck or blow did you put a finger on the vent drain hole? If not, you won’t hear bubbles because you’ll just blow air through the hole.
 
Qotile said:
Are you sure it’s blocked if the tanks are being used evenly? Or do you think the filler cap vents are being used? When you suck or blow did you put a finger on the vent drain hole? If not, you won’t hear bubbles because you’ll just blow air through the hole.
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It has Monarch filler caps. Where are the vent drain holes? I had a 78 C177B and don't remember those. I'd hear bubbles when blowing in from both sides. On this one the left vent is blocked, you simply cannot blow into it. The right vent you can blow into without any resistance at all.
 
You should be able to blow into the vent with very little resistance.
No bubbles unless your tanks are full to the brim (vents are not placed at the bottom of the tank but rather at the top).
And if you suspect obstruction in the vent, it is not recommended to blow because you can end up with the blockage further in the wing or even in the tank.
Lost of dirt bugs love these tiny vents for nesting. Mud bugs especially. A 1ft 1/8" drill bit is a good way to make a temporary hole through their nest but a good cleanout is in order then.

You can use a few inches of silicone or rubber hose to easily make some small (vented) vent caps (with "Remove Before Flight" streamers) for the vents.
They serve two good purposes:
1) they prevent majority of bugs from entering (without obstructing air flow and tank venting while parked)
2) they are great reminders not to bash your head into the wingtip when walking around :)

If needed, I can provide pictures of my home-made vented vent caps, just request it and I'll take a picture next time I am at the airport.
 
BigBadLou said:
You should be able to blow into the vent with very little resistance.
No bubbles unless your tanks are full to the brim (vents are not placed at the bottom of the tank but rather at the top).
And if you suspect obstruction in the vent, it is not recommended to blow because you can end up with the blockage further in the wing or even in the tank.
Lost of dirt bugs love these tiny vents for nesting. Mud bugs especially. A 1ft 1/8" drill bit is a good way to make a temporary hole through their nest but a good cleanout is in order then.

You can use a few inches of silicone or rubber hose to easily make some small (vented) vent caps (with "Remove Before Flight" streamers) for the vents.
They serve two good purposes:
1) they prevent majority of bugs from entering (without obstructing air flow and tank venting while parked)
2) they are great reminders not to bash your head into the wingtip when walking around :)

If needed, I can provide pictures of my home-made vented vent caps, just request it and I'll take a picture next time I am at the airport.
Click to expand...
The mechanic said it was a spider web and got it cleared. There is still some resistance though. I'd like to see a pic of your vent caps, I'll get it to the owner and hope he follows through on it.
 
The vent line drains are in the wing roots. You might see plugs in fittings at the roots near the aft doorpost. They're supposed to come out annually/100 hours to drain any water or other junk. Water corrodes the aluminum tubing from the inside out.

If I was to make any vent caps to keep bugs out, I'd make them of fabric so the vent can still breath if I forget to take them off. "Remove Before Flight" flags rot off, or they can pull the cap off in wind so guys cut the flag off, and so on.
 
luvflyin said:
Where are the vent drain holes?
Click to expand...

There are 0.040 inch holes about 6 inches from the end of the vent. Here's the procedure from the service manual.

12-18. CHECKING FUEL VENTS. Field experience has demonstrated that fuel vents can become plugged, causing possible fuel starvation of the engine. Also, a plugged vent line may allow fuel in a full bay to pressurize the fuel bay cavity due to expansion. following procedure can be used to check the vent system.

(THRU SERIALS 177RG1051 AND F177RG0160)
a. Cover . 040 inch drilled holes approximately 6 inches from end of vent lines at trailing edges of wing tips.
b. Turn fuel selector valve to OFF and remove both fuel bay filler caps.
c. Using rubber tube attached to vent line at trailing edge of wing tip, blow into line. If air can be freely blown into fuel bay, vent line is open.
d. Repeat this procedure for fuel vent in opposite wing tip.

Caution: Be sure to uncover . 040 inch holes in vent lines at wing tips after completion of check.

(BEGINNING WITH SERIALS 177RG1052 AND F177RG0161)
a. Cover . 040 inch drilled holes approximately 6 inches from end of vent lines at trailing edges of wing tips.
b. Turn selector valve to OFF position and remove both fuel bay filler caps.
c. Plug vent line at opposite wing tip.
d. Using rubber tube attached to vent line at trailing edge of wing tip, blow into line. If air can be freely blown into fuel bay, vent line is open.
e. Remove plug at opposite wing tip and install both UNVENTED fuel caps.
f. Again blow into rubber tube. If the vent line interconnect is open, air will emerge from opposite wing tip vent line.
g. Repeat this procedure for vent in opposite wing tip.

Caution: Be sure to uncover drilled holes and ends of vent lines at wing tips after completion of check.
 
Qotile said:
There are 0.040 inch holes about 6 inches from the end of the vent. Here's the procedure from the service manual.

12-18. CHECKING FUEL VENTS. Field experience has demonstrated that fuel vents can become plugged, causing possible fuel starvation of the engine. Also, a plugged vent line may allow fuel in a full bay to pressurize the fuel bay cavity due to expansion. following procedure can be used to check the vent system.

(THRU SERIALS 177RG1051 AND F177RG0160)
a. Cover . 040 inch drilled holes approximately 6 inches from end of vent lines at trailing edges of wing tips.
b. Turn fuel selector valve to OFF and remove both fuel bay filler caps.
c. Using rubber tube attached to vent line at trailing edge of wing tip, blow into line. If air can be freely blown into fuel bay, vent line is open.
d. Repeat this procedure for fuel vent in opposite wing tip.

Caution: Be sure to uncover . 040 inch holes in vent lines at wing tips after completion of check.

(BEGINNING WITH SERIALS 177RG1052 AND F177RG0161)
a. Cover . 040 inch drilled holes approximately 6 inches from end of vent lines at trailing edges of wing tips.
b. Turn selector valve to OFF position and remove both fuel bay filler caps.
c. Plug vent line at opposite wing tip.
d. Using rubber tube attached to vent line at trailing edge of wing tip, blow into line. If air can be freely blown into fuel bay, vent line is open.
e. Remove plug at opposite wing tip and install both UNVENTED fuel caps.
f. Again blow into rubber tube. If the vent line interconnect is open, air will emerge from opposite wing tip vent line.
g. Repeat this procedure for vent in opposite wing tip.

Caution: Be sure to uncover drilled holes and ends of vent lines at wing tips after completion of check.
Click to expand...

Thanks for the details. I'll get them to the mechanic. I'm pretty sure there is still partial blockage even though the mechanic found some spider "stuff" and cleared it out. I can blow into it now, but with some resistance. I'm a little confused about the "unvented" fuel caps reference though. I talked to someone who seems knowlegable and he said vented fuel caps have been required by FAR since sometime early 60's. He was a guy from Hartwig who makes Monarch fuel caps. He told me how to verify the 'caps' are venting. That will be a part of my pre-flight until this is all sorted out.
 
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I put clear tubes on the end of my vents about two inches long. I leave them there and check them at each preflight. Any bug wanting to build a nest won't travel up the tube father than that so I can see any obstruction. No need to remove them.
 
cgrab said:
I put clear tubes on the end of my vents about two inches long. I leave them there and check them at each preflight. Any bug wanting to build a nest won't travel up the tube father than that so I can see any obstruction. No need to remove them.
Click to expand...
Not a bad idea. How do you keep them in place? Glue? Snug fit? Don't they crack and fall of from sun/UV/heat exposure after time?
 
BigBadLou said:
Not a bad idea. How do you keep them in place? Glue? Snug fit? Don't they crack and fall of from sun/UV/heat exposure after time?
Click to expand...

I just slipped them on and they are snug fit. They have yellowed but are still in good shape. I got the idea from a post on the CFO digest.
 
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