whee wrote:I have zero Cessna experience but if it were me I'd chase the issue till I was satisfied that it wasn't a safety of flight problem. I flew a plane quite a bit that fed unevenly from each tank. I didn't think it was an issue till it became a glider with one tank still half full. I'm chicken, fuel system issue scare me.

I'd be interested in knowing just what caused that.
I've owned three Cessna taildraggers, they all had uneven feeding issues - some more than others.
I don't really worry about it any more-- I just put the selector on both and fly.
A friend of mine had a procedure of taking off on both, switching to left for a timed half hour, then switching to right & timing it until it ran dry. Then the left tank would have that much time in it, minus the original half hour. Sounded like a lot of trouble to me, and a lot of room for screwing it up. He told me I was a fool (!!) for flying with the selector on both. But until now, I don't think I've ever heard of an airplane that quit due to fuel starvation with the selector on both if there was any fuel in it-- usually the problem is mismanagement of the selector(s) by the pilot.

BTV wrote:My tanks have the interconnect. I put a hose over the vent and blew through it today. Could hear air coming through each tank with the cap off. Took the caps apart and they are clean and in good shape. ...

Hard to believe you're getting a
vacuum in the tank(s) if both the vent system and the vented caps are working right. What style caps do you have? About 4 years ago, I replaced both caps on my old C150TD with vented Cessna caps @ about $50 each. I had possible fuel flow issues and I figured $100 was cheap to have peace of mind about the caps.

I usually start here...

Does not matter which make/model of light aircraft:

Drain it, level it and read the gauges by adding (5) gallons at a time. Log it, date it. I also placard the readings on my Scout in the cockpit. Also, verifying at the pump helps each time too.

Then we know if the gauges are correct or not. Obstructions and/or venting are usually then considered.

8GCBC wrote:....Drain it, level it and read the gauges by adding (5) gallons at a time. Log it, date it. I also placard the readings on my Scout in the cockpit. Also, verifying at the pump helps each time too.
Then we know if the gauges are correct or not. Obstructions and/or venting are usually then considered.

Me too, but I do it three-point. Level isn't important to me because I never trust the fuel gauges in flight.
Fill the tanks 5 (or whatever) gallons at a time, dip them (a paint stick from Sherwin Williams works great) and mark the dipper.
I dip the tanks every time I fuel up, write the tach time & fuel-on-board down on a piece of tape, and stick the tape on the panel. I have a darned good idea of my fuel burn so can calculate how much fuel's left just by looking at the tach time & doing some math: 11 gph = 1.1 gallon every six minutes, one five gallon can of mogas (filled to 5.5) for every half hour of flight. I'm always within about a gallon of my fuel-burned calculation. It's a poor man's fuel totalizer, only way easier to re-zero if I were to forget to dip after gassing up.

hotrod180 wrote:

8GCBC wrote:....Drain it, level it and read the gauges by adding (5) gallons at a time. Log it, date it. I also placard the readings on my Scout in the cockpit. Also, verifying at the pump helps each time too.
Then we know if the gauges are correct or not. Obstructions and/or venting are usually then considered.

Me too, but I do it three-point. Level isn't important to me because I never trust the fuel gauges in flight.
Fill the tanks 5 (or whatever) gallons at a time, dip them (a paint stick from Sherwin Williams works great) and mark the dipper.
I dip the tanks every time I fuel up, write the tach time & fuel-on-board down on a piece of tape, and stick the tape on the panel. I have a darned good idea of my fuel burn so can calculate how much fuel's left just by looking at the tach time & doing some math: 11 gph = 1.1 gallon every six minutes, one five gallon can of mogas (filled to 5.5) for every half hour of flight. I'm always within about a gallon of my fuel-burned calculation. It's a poor man's fuel totalizer, only way easier to re-zero if I were to forget to dip after gassing up.

Better be safe than sorry! You are using a system that is hard to beat. I wish more would too.

Thanks for all the replies.

Looks like everything is working as it should be. I adjusted the vent back down (a little lower than Cessna spec) and now no vacuum on tanks. Flew about 1.5 hours today and fuel burned from each tank was within one gallon with selector set to both.

Edit: Oops, looks like your problem is solved.
<snip>

Just FYI, In the NTSB accident report on our airplanes wreck many many years ago before we owned it, it mentions that the strut cuffs were not installed properly, and were missing a piece of seal. Supposedly this can set up a situation where there is a vacuum in the fuel vent.
According to Cessna Service Bulletin SEB88-2 "Excessive gaps between wing strut and cuff can cause fuel bladder think wrinkling, unsnapping and inaccurate fuel quantity indications."

Cessna 1955 180 incident
The top of the wing fuel vent is a definite killer waiting to get you -- especially in northern latitudes subject to icing, Icing does not have to be visible!!! I went down with visual ice and a fuselage covered with 80/87 fuel -- but the gauges indicated plenty of fuel -- just in the wrong place. when the syphoning was completed through the vent tubes, both gauges went to zero (cork float type wing gauges on a '55) and the prop went to zero also. I was on the ground in 3.5 hrs and should have had another hour and 1/2 of fuel on board. Survived that one into a logged off clearing. A year later, again on fuel management protocal, in snow and finally made the clasic 180 turn --- I started noting erronous fuel readings again. Since that had only happened once, I landed on a ocean beach and jumped up on the wing strut to check the vent --- a pigeon wing of ice was growing on the vent. I broke the ice off, sucked on the vent tube to free the "pea" , added 12 gallons that I had on board as an extra, and noted the fuel trail again from the vent , down the wing and onto the fuselage. I then flew across the bay, and noted that by time airborne and fuel added, I had syphoned 20 gallons overboard. Gentlemen and Ladies !! ----- a placard saying "fuel loss due to inadvertant icing" will kill you !! Inadvertant means just that! You didn't mean to be in icing conditions, but it was unpredicted and you might be past the "point of no return". I happen to know Barry Schiff (Writter for AOPA magazine) suffered a fuel loss from Redding to Oregon, in the winter, and didn't have a clue where 15 gallons went since the fuel trail had washed off of the a/c ! BTW, the fuel trail was gone in my first incident 5 minutes after dead sticking into a logged off clearing ---- a passing shower would have made a fatal crash look like pilot error of being lost and running out of fuel . I'll bet there are a number of fatal Alaskan crashes due to this factory error !