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RV-8A fuel smell after landing

pv9

Member
Hi folks:
I just “adopted” my recently purchased and RV-8A and did my transition training. It is a wonderful aircraft to fly. Lots of minor squawks but a possibly worriesome one that I wanted to consult the experts on this forum on.
I have a carbureted O-360.
After landing with the fuel boost pump on and mixture rich I get a smell of fuel that goes away. This happens every time on landing:
 
Look for the telltale blue stains on the fuel runs aft of the firewall, including wing root. Don’t forget to look at the vent lines as well.

Here a small air leak will show up as a fuel smell after running the boost pump for landing. The RV-8/8A fuel line plumbing is challenging - and a source of hours of “loosing your religion” work.

Carl
 
Look for the telltale blue stains on the fuel runs aft of the firewall, including wing root. Don’t forget to look at the vent lines as well.

Here a small air leak will show up as a fuel smell after running the boost pump for landing. The RV-8/8A fuel line plumbing is challenging - and a source of hours of “loosing your religion” work.

Carl

Thank you so much. I will troubleshoot based on this valuable tip!
 
I had a tank leak develop at the famous aft baffle seam. It was small enough I couldn’t see any evidence of it externally but found it with a borescope. I could smell it in the cockpit after landing for some reason.

Good hunting
 
Probably not your case, but the -8 is well known to give a fuel smell with full tanks in the pattern because it burps a little fuel out the tank vents, and this migrates into the under-wing passenger vent. It seems more common with a full right tank than left (probably because that is the side the vent is on).

If you’re sure it only occurs with the pump on, then you might well have a leak somewhere - but since you’re new to the -8, figured you should know of this “characteristic”. I think other models will burp fuel out the vents as well, but they don’t have an under-wing vent to pipe the fuel into the cockpit.
 
Value of VAF

Ironflight,
This is one of the many reasons this VAF forum is so valuable! Pearls like this. Funny thing was when I saw the post I thought what the heck, then read it and went oh yeah, just took that "uniqueness" for granted everyone else knows this. Nice to keep sharing the nuisances of each airplane type.
Thanks!
 
Probably not your case, but the -8 is well known to give a fuel smell with full tanks in the pattern because it burps a little fuel out the tank vents, and this migrates into the under-wing passenger vent. It seems more common with a full right tank than left (probably because that is the side the vent is on).

If you’re sure it only occurs with the pump on, then you might well have a leak somewhere - but since you’re new to the -8, figured you should know of this “characteristic”. I think other models will burp fuel out the vents as well, but they don’t have an under-wing vent to pipe the fuel into the cockpit.

I found these blue telltale signs by the fuel flow transducer cube.
The area around it was dry but there was an oily residue near the corners. It appears that there is a very small amount of vapor coming from there. Aircraft is grounded until this can be traced and fixed!
 

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Its hard to tell from the photo, but it looks like there may be Teflon tape on the blue threaded fitting going into the red cube. If that is the case it should be removed and replace with a more appropriate thread sealant (lots of debate on VAF regarding favorite products).
 
Its hard to tell from the photo, but it looks like there may be Teflon tape on the blue threaded fitting going into the red cube. If that is the case it should be removed and replace with a more appropriate thread sealant (lots of debate on VAF regarding favorite products).

It could be teflon tape. If so, serious builder error. I'm going to have to inspect everything at this point.
 
Looks like this was a recent “repair” by an A&P who attempted to fix a faulty fuel PSI reading. He put a mechanical gauge in line with the cube transducer to check the PSI and then re-sealed it with Teflon tape.
Lesson learned. Do your own repairs, trust almost nobody.
 
Fuel line

While you're at it also check the fuel line that leads to the red cube - in the photo it appears as if the bend is kinked and a bit flattened and has a slight dent, possibly from when the line was temporarily removed to insert the test gauge.
 
Good catch! They pushed the fuel lines apart to make room for the gauge and slightly bent the hose.
 
And while you're down there... maybe it's just the angle of the photo, but it looks like the fuel flow transducer is just hanging in space, supported only by the fuel lines connected to it. If that's the case, I'd worry about something cracking eventually.
 
If you are going to rework the red cube, then use the opportunity to move it to a better location. I suggest just after the mechanical fuel pump, using adel clamps to mount it on the engine mount - not the engine.

Follow the normal rules - no right angle fittings, fuel line on the output side running slightly up hill, etc.

Carl
 
I was told not to put the fuel pressure transducer or the boost pump in the engine compartment due to the heat generated by the exhaust. Is that just hearsay?
Thank you.
 
Typical install is the boost pump and fuel selector on the cabin side of the firewall. Fuel filter may or may not be.

Fuel flow sender on the engine side of the firewall, between the mechanical fuel pump and the engine. Fuel pressure sender on the firewall, tapped into the output of the mechanical fuel pump.

Carl
 
Typical install is the boost pump and fuel selector on the cabin side of the firewall. Fuel filter may or may not be.

Fuel flow sender on the engine side of the firewall, between the mechanical fuel pump and the engine. Fuel pressure sender on the firewall, tapped into the output of the mechanical fuel pump.

Carl

Looks like everything is as you suggested except the fuel pressure sender which should be relocated outside. The boost pump is on the cabin side.
Thank you for spotting that.
 
Looks like everything is as you suggested except the fuel pressure sender which should be relocated outside. The boost pump is on the cabin side.
Thank you for spotting that.

Nope - looking at your photo your fuel flow sender (red cube) is on the cabin side of the firewall, not mounted at all - the photo suggest it is suspended just by the fuel lines. That alone is a fuel leak waiting to happen.

Carl
 
Thank you. The cube was a recent addition by an A&P and I will be sure to relocate it on the other side of the firewall.

I've grounded the aircraft and am going through pretty much everything with a fine tooth comb at this point.
 
fuel system schematic

Thank you. The cube was a recent addition by an A&P and I will be sure to relocate it on the other side of the firewall.

I've grounded the aircraft and am going through pretty much everything with a fine tooth comb at this point.

Sent you a PM with my fuel system schematic for a reference. Your system should be the same since we both have carb'd engines.
 
Thank you so much. That was fortunately not Teflon. It was approved permatex fuel sealant. Now the hard part of relocating the fuel flow transducer.
 
Fuel Smell

Don't fprget to check the airbox for the drain holes that don't always get drilled during construction. See Vic Syracuse' column on this issue in the forums.
 
Thank you all so much. I have located the smell to the fuel vents that are pretty close to the exhaust ramp. The exhaust ramp has some cracks that are stop drilled (common problem on the 8A it seems).
After landing with a hot engine the vents have a pretty strong fuel smell that makes its way into the cabin.
 
Thank you all so much. I have located the smell to the fuel vents that are pretty close to the exhaust ramp. The exhaust ramp has some cracks that are stop drilled (common problem on the 8A it seems).
After landing with a hot engine the vents have a pretty strong fuel smell that makes its way into the cabin.

Remember you have blue stains on the floor near your rudder pedals. This is only a result of a fuel leak.

The exhaust ramp does need attention as it could be a source of Carbon Monoxide into the cabin. Pro-seal is a good option to seal it up.

Carl
 
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