182Q Fuel Questions

[WCG]

Hello all, new to the forum and have an question about 182s. I have a 182Q and just had an EI CGR installed. I've only flown it a couple of times since the engine monitor was installed. When the CGR installation was complete, both tanks were full of fuel. Yesterday I refilled both tanks for the first time since the installation. I noticed that the right wing fuel cap went on slightly differently but didn't pay too much attention - I could feel a slight difference in the twist of the cap. With both tanks completely full, I took off and noticed the left fuel gauge dropping as expected but the right tank remained completely full. I switched the fuel selector between left, both and right multiple times yet the right gauge remained full. I rocked the wings several times and no change. I thought the CGR may have bad sender so when I got back to the hangar I popped off both caps. Turns out that the CGR was accurate - when I stuck each tank, the reading was accurate and the right tank was completely full. I could also see the right wing fuel tank filled to the very top.

I called my mechanic who installed the CGR and AirPlains who did the engine conversion years ago and explained the situation. Both said that they haven't seen this exact situation but it could very well be the right fuel cap (remember I said that the right fuel cap went on a bit differently when I replaced it after refueling). The weird part is that the right tank was completely full and the engine did not sputter when switched on right tank only. AirPlains thought this could be the result of the left tank being pressurized and feeding the right tank fuel thus causing the right tank to remain full. Even though a full tank would suggest that no fuel was used from the right tank, it may in fact be the case that the right tank fed the engine and the left tank fed the right tank causing the right tank to remain full. Note that the vents are properly positioned behind the struts - this was checked by the a&p.

So my question is whether anyone experienced similar issues with fuel cap venting or related fuel balance issues on a 182Q (note no bladders) and if they have any explanations.

Thank you!

 

[Magman]

The “loose” cap may well be the culprit. Fuel will move around due to a pressure

differential. Suggest you pressurize vent ( VIA MOUTH ONLY) and use soap and

water to check for leakage.

I had an issue like this but it was with long range bladder type that had the

vent line in the tank installed incorrectly. This also permitted fuel to transfer.

It sounds like you have an IO-520 upgrade?

What tank does the fuel return go to?

 

[WCG]

Thanks for the reply. I have the IO-550 upgrade and fuel return goes to right tank. Funny thing is that the fuel balance was perfectly fine until I refueled (well, as about as perfect as you can get in a 182 from what I am learning).

 

[ServoB17]

If you're a member of CPA, they've got a pretty detailed tech note on this common problem. I have a '78 Q (O-470) with bladders, and it's only vented on the left. On a normal flight the left tank will drop to about 3/4-2/3 full before the right starts to drop. Two vents help, but these tanks are connected through the vent line, and at some point Cessna also connected the fuel feed line to the vent line between the two tanks. Any pressure imbalance between the two sides can easily push fuel around regardless of the fuel selector.

I used to occasionally switch to the right tank, but now I just leave it on both and it never gets too bad.

 

[WCG]

Appreciate the reply. Next time I'm at the hangar I'm going to do the blow test on both vent lines as well as swapping the fuel caps between right and left tanks - there was a thought that could help with the flow / balance issues. Also need to ensure that both caps are on the tanks properly...

 

[Randomskylane]

Yours is newer and has a different system etc but I remember after buying mine sticking the tank after landing and then the next day/week and marveling at the cross tank fuel movement. After a few checks I was comfortable that nothing was lost/leaking/stolen etc

enjoy

 

[Magman]

Since Servo brought up bladders:

Investigating similar symptoms as WCG led to discovering improper vent line

installation in the Tank.

These long range bladders incorporated “ loops” to support the plastic(?) vent lines

in the tank. Thus LEFT and RIGHT tanks had interconnections through the fuselage

and on to the the other tank.

For some reason the in- tank lines were not passed through the loops.

This allowed the lines to remain immersed in the fuel.

So rather than than air/fumes moving it was the fuel that did so.

As the LEFT tank was directly pressurized from the external vent tube ,

the fuel in that tank transferred to the RIGHT tank via submerged vent

lines.

So; if you flew while operating on the RIGHT tank you would see the

LEFT tank quantity drop.

 

[Gary Ward]

Welcome to POA.
I was lucky enough to talk with Butch Hartwig last year during a fuel tank replacement in my 172. He is a expert on fuel tanks especially cessna. He discussed in detail how important fuel tank vent tube placement is. He sent me about 5 pages on how to measure fuel tank vent tube placement. It needs to be within a few thousands of inch, surprising tolerances.
Also like said above Cessna Owners Pilots Magazine published a story how it is important that Butch sent me also. If your tanks are not drawing down properly than the vent may need adjustment according to Butch. They really are the best place to take a leak.