Z W

I'd like to see a test where a painted "tank" with a Mooney-style SAF fuel sump is filled with G100UL and then made to slowly leak out the sump, or maybe from a leaking rivet, with a timelapse camera pointed at it for a week. That would be the best real-world test. I don't plan to soak any inspection panels in fuel, but I'm pretty sure at some point the above will happen again on my plane.

Also I've never had this happen from idling before. The plane is properly adjusted to idle at 700 RPM or so. I parked it as normal in my home hangar, using the same power settings and practices. Now that you mention it, I always do give it an RPM boost to finish turning it around to back it into the T-hangar before shutting off the engine, which would naturally run the scavenger pump as suggested. But something has changed.

Thanks for the thoughts and information. I'll focus on the lines and valves. The thinking to overhaul the turbo too is based on: 1) I am not confident on when it was last overhauled. According to the logbooks, it was 2,700 hours ago in 1988. The engine got an overhaul a little over 1,400 hours ago in 2004, including the lower end with new bearings and all new cylinders, but the turbo system was not done or if it was there was no log of it. It did not qualify as a legal major overhaul. I have reason to believe some of the previous owners were not all that diligent about logging work done on the plane, though that is not obvious from just reading the logbooks. We have put a little over 1,100 known hours on this turbo. 2) Recent failure to develop full MP on takeoff and occasional MP fluctuations during flight. I'm now wondering if the turbo bearings are going and causing rubbing of the blades occasionally. We have overhauled the turbo controller and wastegate, but not the turbo itself. The MP fluctuations I've seen before, and cured with overhauling the controller and lubricating the wastegate, and the loss of 1 inch on the takeoff roll could just be instrumentation or environment changes, but I'm not feeling confident about it. Lately I've been subscribing to the idea of overhauling critical components before they fail and scrub a trip and/or leave me stranded somewhere, at best, or create a life threatening safety situation at worst. I'm typing this from a hotel that's halfway through an 8-hour drive I'm making because I canceled the flight due to this leak. I don't want to waste money and am also aware of maintenance induced failures. Hard line to walk. When I get back I may borescope the turbo and see if I can find any play in the bearings, just to know. But I'm still leaning towards sending it out either way.

Arrived at the hangar to a surprise today - a puddle of oil under the end of my exhaust pipe. Pictures below. Plane last flew about 3 weeks ago for 0.6 hours without issue, has been parked since then. Have not had to do any maintenance to this turbo in 14 years of ownership. No record in the logbooks of it being worked on since 1988 when it was installed with the engine. So it doesn't owe me anything. Had been considering sending it out for a preventative overhaul anyways. No problems with it except maybe, lately, I've been seeing 35 inches of MP instead of 36 on takeoff sometimes, and once, in flight, had MP fluctuations of 1-2 inches for about 15 minutes before it quit and went back to normal. I had about convinced myself it was just density altitude/temperature/winds or something. I applied mouse milk to the wastegate and it did not repeat. TSIO-360-MB engine. Searching here says it could be a problem with the check valves in the oil lines, which can be inspected/cleaned. The oil lines themselves look a little aged, may see if I can have those replaced/overhauled as well. I plan to have the turbo overhauled. A&P can't come look at it until maybe Monday at the earliest, so I have some time for some internet research. New V-band clamp is on order. Showing expected in stock 1/13/2025 for the V-band through Air Power. Hope that date is correct. Best I can tell, it should be the new riveted style clamp, part number 670105. Any other ideas/suggestions while I'm at this? Thanks in advance.

If a nitrile O-ring is available from Aircraft Spruce with a MS part number and costs $0.25, but a Viton O-ring is also available, either from Aircraft Spruce or elsewhere, for $1.50, and is identical in size and function but will not swell if exposed to high-aromatic 100LL or G100UL gas and lasts 10x as long, and will not deform if exposed to high pressure, I would happily pay you or another A&P/IA to research that and install the superior product. Maybe just me, but there's one data point.

I am not an A&P nor an IA, but I believe most of us are flying around in airplanes that may no longer conform exactly to the type design and that are full of parts not shown in the parts catalog. Examples include starter and main power solenoids, voltage regulators, SCAT/SCEET tubing, fine wire spark plugs, engine baffle seals, door and window seals, main ship batteries, and many other parts where the OEM part is no longer available but FAA-PMA replacement parts exist. My understanding of this is that an A&P or IA could swap out a nitrile O-ring with an identical one made of Viton if they are confident it will not impact the service of the part or the airworthiness of the aircraft. Am I wrong?

Mr. Braley posted some guidance from the FAA recommending replacing nitrile O-rings with equivalent Viton or Fluorosilicone. I'm certain some A&P legal scholars will weigh in soon, but I believe there's an accepted practice to do that. Not recommending anyone go out and install the wrong O-rings in their plane.

I learned some things about O-rings from all this. I guess I shouldn't be surprised the world continues to use and sell inferior-grade materials that are a few pennies cheaper. Viton O-rings appear to be easily available for purchase for not a lot of money.

Well, I will double-check my installation then. Makes me wonder if my TOGA is set higher than 7 degrees.

The AFM supplement for the GFC500 for a M20M (shown below) says TOGA establishes a 7 degree nose up pitch. I thought I had a scan of mine but can't find it right now. Calling it Vx was inaccurate on my part, although I believe it produces performance close to that at full power, but I do know it is referencing pitch, not airspeed. In my plane it's enough nose up pitch to startle passengers who are not expecting it and is more nose up pitch than I like to use on a standard climb-out for sure.

Nice post. I don't like to use the TO/GO for a normal takeoff though. The attitude it provides to give Vx, while what you want on a go-around in IMC, is too nose-high for a normal departure. It also then requires that you re-configure the autopilot entirely for your first turn - You must press HDG or NAV, then VS or IAS, then dial in your preferred VS or IAS on the wheel, then press "AP", all while possibly bumping around, entering IMC, talking to ATC, etc. Instead I prefer to configure the autopilot to fly my planned departure, which means flight director on, heading mode engaged, heading set to runway heading, vertical speed set to 500+ FPM, altitude bug set. This allows me to follow the flight director and heading bug on takeoff manually until 500 feet AGL, then engage the autopilot and be fully configured just by pressing the "AP" button. Also passing 500 feet AGL I will roll the heading bug over to my assigned heading, or enter NAV mode to go on-course, whichever is appropriate. An alternative to this is instead of HDG, to leave it in ROL mode, and pre-set your heading bug to your assigned heading if you have one. So when you begin your first turn and press the AP button, you just also press HDG and you're configured and don't have to remember what your assigned heading was during takeoff. This maybe works better and removes one item you have to remember (your assigned heading), but I like having the heading bug available to follow to fly runway heading, in addition to the flight director, which in this scenario is not actually tracking runway heading. So for me, the TO/GO is more of a GO button. But I'm curious to hear if anyone sees issues with what I've developed above as my practice or does it differently. A note - I had to add each of the autopilot configuration steps to my pre-taxi checklist to start getting it all right, after the GFC500 was installed. Highly recommend that to anyone learning this new autopilot - there are a lot of configurations you can make on the ground to make your life easier right after takeoff.

Had it once due to an air intake restriction caused by a poor air intake box repair. Restricted air intake prevented the turbo from spooling up to full power. Also caused the alternate air door to open and that light to come on. Could be a lot of things, unfortunately, but there's one.

I had a fuel pressure gauge that would occasionally drop to 0. Sure got your attention, but the engine never faltered. New sensor, new fittings, checked the connections, no more problems.

I've had leaks patched by small local shops a few times, at a cost of a few hundred dollars here and there. My tanks have not been fully resealed since 1982, as far as I can tell from the logs. It's a maintenance item, but nothing to be too concerned about. Every model of plane has its maintenance issues. Cheaper than a parachute repack. You could also buy a plane that was resealed 5 years ago and have it start leaking after your first bounced landing, so just be prepared. Many (most?) leaks can be left alone until the next annual or the next time it's in the shop. They result in stains on the wings but often the fuel evaporates before it even drips on the ground. I've never had one that was a flight safety issue or would ground the plane.

I'll be glad to not splash liquid lead on my hands sumping tanks, and I'll be glad to get it out of my engine and oil too, when that becomes possible. I'll be even more glad if it keeps an overreaching government wanting to ban lead from grounding the fleet. If a side effect is that some of the sealant in my fuel tanks, which is up to 42 years old at this point where it hasn't been patched, has to be replaced to run a new modern lead-free fuel, I will call it a cost of keeping a 42-year-old airplane in the air. I just hope I can find a shop to do the work. If it seeps and causes my 12-year-old paint, applied by a reputable shop and still in excellent shape, to bubble off, then I'd say there's a problem. From everything I've read about GAMI's testing, I don't think it will. I expect by the time this fuel is available to me in the Midwest, if that's what it does, everyone will know about it.