Air bubble of doom in gascolator!

[4BravoWhiskey]

I was thinking about that exact idea yesterday!!! I have one and just might give it a try.

[n2582d]

I think Tim may be on the right track in thinking about vapor lock. Except for the change from the gooseneck vent, the 170 fuel system is virtually identical to the early 172's which were subject to AD 72-07-02. I would make sure the gooseneck vent is unobstructed and that both tanks have vented caps that are working. Also check that the inter-tank vent line which the gooseneck is connected to is as flat as possible, i.e. not sagging down. Then, if this occurs again, see if switching to a single tank corrects the fuel starvation problem. The applicable C-172 Service Bulletins in the Maintenance Library are included here.

Finally, I'm reminded of a friend of mine who was able to keep a C-150 going after carb problems caused the engine to begin to quit. He used the primer to keep the engine running. Of course if there is air in the gascolator at the primer line intake this technique may not help much.

[GAHorn]

I've never understood how switching to a single tank can prevent vapor lock on that AD. Can someone explain it?

I don't know if this is the real answer or not... but running on one tank (vs two) will increase fuel-flow in the supply line, which may reduce the amount of time fuel may stagnate and absorb heat.

[hilltop170]

I have no idea whether my gascolator has a bubble in it or not, it is metal and I can't see thru it! But the engine has never quit either, no matter how hot the ambient is or how long it sits after shutdown, it always starts quickly and keeps running. This is still baffling to me.

[4BravoWhiskey]

Well maybe if mine were metal I wouldn't have this problem!

Couldn't reproduce an air bubble on the ground no matter what. I mounted a GoPro near the gascolator, it was working great until the battery died 5 minutes into the flight. doh. I'll try again soon with charged batteries. I could even monitor it on my iPhone in the cockpit during flight! I flew for nearly an hour anyway (high, and over the field) and didn't get any air bubble.

But the new EI oil temp/pressure gauge works fantastic, as do the new push-to-talk switches. So at least there new lights and digits to look at, and buttons to push!

[GAHorn]

Well maybe if mine were metal I wouldn't have this problem!

Couldn't reproduce an air bubble on the ground no matter what. I mounted a GoPro near the gascolator, it was working great until the battery died 5 minutes into the flight. doh. I'll try again soon with charged batteries. I could even monitor it on my iPhone in the cockpit during flight! I flew for nearly an hour anyway (high, and over the field) and didn't get any air bubble.

But the new EI oil temp/pressure gauge works fantastic, as do the new push-to-talk switches. So at least there new lights and digits to look at, and buttons to push!

Maybe the new gizmos will distract you so you can forget about bubbles....

[MoonlightVFR]

Is there a final solution to bubble of doom observation?


Is there still a bubble in gascolator?


Have we built up our knowledge base on operating the C170?


Regards

[4BravoWhiskey]

No solution yet.

However, brace yourselves for the most exciting flying video of all time:
https://youtu.be/eQIiGP5tkVU

Prior to this flight I replaced the gaskets on the gascolator with the Cessna versions (George). I haven't had a chance to bypass the fuel flow sensor with a new fuel line. That'll be next.

HOWEVER, I also noticed after the two 45-min legs, where this occurred on the second leg, I had burned a lot more from the right tank (12 gal) than from the left tank (3 gal). Engine ran perfectly the whole time. On the return, I tried left tank only for 30 min, and there were no issues at all, and no air bubble after that leg. So if it is somehow a venting issue, it's intermittent.

[4BravoWhiskey]

(and btw my carb does NOT have an accelerator pump, so that's why it needs a bit of primer to start.)

[blueldr]

As a matter of curiousity, what is the complete part number of your carburetor?

[4BravoWhiskey]

Yes the camera was attached to the engine mount.

Don't know the carb model # but will check next time I'm out there.

I'm gradually adding some more interesting flying videos (didn't think that was possible did you??) to my YouTube channel. In fact, a couple of clips from one of the coolest flights ever been on, several years back. Click on my name in YouTube and you can find them. I'll add more soon.

[Bruce Fenstermacher]

Does the bubble get bigger than that?

I don't know if that is enough to worry about. Heck my gascolator may have a bubble that big in it. Now I'm going to have to mount a camera and watch it. See what you've done now.

[4BravoWhiskey]

Well when it gets to be 3/4" tall or more, I think it's a problem. It certainly seemed to be a real problem when I was flying in Utah that time.

I was actually wondering if people might start checking their gascolators at the end of their flights and just see. Because normally one checks before a flight, not at the end, and ometimes I have seen that the bubble goes away overnight. Maybe a little bit of air is not entirely unusual... although I still don't see how it gets in there.

[Bruce Fenstermacher]

I don't know if it is a problem. And I didn't have your problem in Utah. If I had your problem in Utah and I was convinced as you are it had something to do with it, I'd be chasing it just like you are.

Just keep in mind that, it is entirely possible your trouble in Utah had nothing to do with the bubble. And that a bubble is normal.

We need more Go Pro owners to monitor their gascolators.

[hilltop170]

That vapor has to come from somewhere! The only logical place is tiny entrained bubbles in the lines from the tanks that coelesce in the strainer. I bet your's is not the only one that does that.