The Cessna 120-140 Association Forum

During a cold spell (lows in the single digits) I found a clear, sticky, gel-like substance on the right fuel sump and on the cowling below the air filter. The tank was half-full with mogas. The left tank was full with no sticky residue. Is this the result of water condensing in the half-full tank? From what I've read, the water in fuel may form ice crystals but I haven't found anything about it turning to gel. I'm assuming once it warms-up, the water will turn to liquid and I'll be able to drain it. Is that correct?

Lora, I can't answer as I haven't experienced the "gel" and (fortunately ) don't dwell in area with temps that low. That said, my guess would be some (very cold) oil residue up front below air intake area...but, at the sump, IDK. How long had it been since you'd drained fuel from that tank sump? ...just thinking that it could be old fuel mixed with some gunk in tank(?). Prob unrelated, but I recall a gent @ OSH several years back who'd purchased a 140 there & discovered that neither tank sump would drain...both apparently totally plugged up with accumulated gunk. Sorry I can't be of more help -- maybe there'll be others who'll wade in here with answers. You might post the question to the "140 Facebook group" as I understand that there's much more activity there. Mac

Hi
I have no idea what it is, but its not water. When water freezes in fuel (Avgas or Jet but cant speak for Mogas) it turns from liquid, or from liquid in suspension directly to ice; very very dangerous as it will very quickly clog a fuel line or filter. One study showed that water could remain as liquid down to -36.6C then instantly turn solid on encountering a fuel line.

Maybe a picture might help an expert diagnose?

Si

Thanks for the responses! There was still some sticky gel this weekend so I drained the tank and removed the sump. There was the sticky gunk around the the threads (tried to attach a picture but I don't think it worked). Cleaned it off, filled the tank with fuel, did a ground run and then flew for two hours with no problem. I fly the plane about once a week and sump it every time. I'm guessing it was just some junk in the tank and probably unrelated to the cowling, which seems like oil residue and possibly some of the stickiness from the air filter. I think the gel on the sump had me searching extra hard all over the plane

A Brackett air filter is sort infamous for sticky oil, on the bag the filter comes in it says to blot off the excess but many don’t so the gooey oil can run out some

Yes, and also why they require annual replacement, low time flight time or not!