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Vapor lock?


ltdoyle

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I did a hot start and probably flooded the engine on my J model yesterday at Mineral Wells, Tx.  It was probably 100 in the shade.  No big problem though, I just did a flooded engine start and it started up and cleared ok.  I taxied to the runway and did a normal run up and takeoff.  After lifting off, I could feel a small vibration and just had that gut feeling that something wasn't right.  I was full rich, full rpm, and wot.  Everything looked ok, until I looked at my analog EGT, which was at peak EGT. I checked to make sure I was full rich, then I started to lean, but she told me that was a no no.  At first I thought maybe I had  broken mixture cable.

When I got enough altitude, I pumped the throttle from wot to closed and back to wot and the engine cleared and EGT went back to normal.  The rest of the flight was normal. I have about 30 SMOH, and have never run anything but 100LL..  In the summer, in Texas, I usually leave my cowl flaps open unless I get up high and cool.  I can only guess I was maybe a little vapor locked.  Anyone else have a similar experience?

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Yikes.  I'd have required clean underwear afterwards.

Do you have a FF gauge and/or an engine monitor that records fuel flow?  My takeoff callouts are:

  • Fuel pressure green
  • Fuel flow 16 (gph)
  • Engine (oil pressure and temp) green and (EGT's on the engine monitor) even
  • Airspeed live, 60 pull (65 rotate)

Hopefully that would catch a situation like that before liftoff...

 

 

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Jay, sorry, I don't have a fuel flow or engine monitor, 201er, good point.  I really can't say if I was leaned when taxing since it was a really short taxi.  I have new Tempest fine wires, but a fouled plug could be possible.  I have never seen peak EGT when full rich.  Just hope it doesn't ever happen again.

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No way to ever know what it was without an full engine monitor. But vapor lock is an excellent guess, but it also could have been a partially obstructed injector. But I don't even know what engine this as a Tapatalk user if you don't tell us, but assume it's injected. It's definitely the season for vapor lock issues and I having been seeing lots of it going around.


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19 minutes ago, kortopates said:

No way to ever know what it was without an full engine monitor. But vapor lock is an excellent guess, but it also could have been a partially obstructed injector. But I don't even know what engine this as a Tapatalk user if you don't tell us, but assume it's injected. It's definitely the season for vapor lock issues and I having been seeing lots of it going around.


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What kinds of symptoms are you seeing for vapor lock issues?  High power too or just popping on approach?  

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2 hours ago, jaylw314 said:

Yikes.  I'd have required clean underwear afterwards.

Do you have a FF gauge and/or an engine monitor that records fuel flow?  My takeoff callouts are:

  • Fuel pressure green
  • Fuel flow 16 (gph)
  • Engine (oil pressure and temp) green and (EGT's on the engine monitor) even
  • Airspeed live, 60 pull (65 rotate)

Hopefully that would catch a situation like that before liftoff...

 

 

16gph? Seems kind of low from sea level, I used to get 16.9 with a bad Cam and my friend’s Mooney gets 19, as did my plane long ago 

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What kinds of symptoms are you seeing for vapor lock issues?  High power too or just popping on approach?  

Fluctuating fuel pressure, if significant enough resulting in fluctuating EGTs and engine roughness that feels like missing but isn't ignition misfire.
Don't see it on approach since those are usually coolest temps inside inside cowling. But full rich coughing on approach is usually too rich of an idle mixture.
Most prevalent on takeoff and initial climb at high OATs but often doesn't appear till in the upper teens in climb. Usually clears in cruise with more airflow but at high temps sometimes the boost pump is needed to be on while in cruise at or above 18k the entire time.
It can be minor roughness or full on partial power loss if EGTs skyrocket. Very insidious.


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49 minutes ago, jkarch said:

16gph? Seems kind of low from sea level, I used to get 16.9 with a bad Cam and my friend’s Mooney gets 19, as did my plane long ago 

I call out "16" as the minimum go/no-go fuel flow.   I actually get 16.9 gph typically, although it might a couple seconds to get up there, but it's also faster to say "16" than "16.9" :)

 

1 hour ago, kortopates said:

No way to ever know what it was without an full engine monitor. But vapor lock is an excellent guess, but it also could have been a partially obstructed injector. But I don't even know what engine this as a Tapatalk user if you don't tell us, but assume it's injected. It's definitely the season for vapor lock issues and I having been seeing lots of it going around.

He did mention he had a J, so presumably an IO-360

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1 hour ago, jaylw314 said:

I call out "16" as the minimum go/no-go fuel flow.   I actually get 16.9 gph typically, although it might a couple seconds to get up there, but it's also faster to say "16" than "16.9" :)

I'd still check that. The Owners Manual for my C says 18.2 gph at sea level, WOT / 2700; I can't imagine that your J is happy with less fuel, since it's supposed to make 10% more power.

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6 hours ago, ltdoyle said:

I did a hot start and probably flooded the engine on my J model yesterday at Mineral Wells, Tx.  It was probably 100 in the shade.  No big problem though, I just did a flooded engine start and it started up and cleared ok.  I taxied to the runway and did a normal run up and takeoff.  After lifting off, I could feel a small vibration and just had that gut feeling that something wasn't right.  I was full rich, full rpm, and wot.  Everything looked ok, until I looked at my analog EGT, which was at peak EGT. I checked to make sure I was full rich, then I started to lean, but she told me that was a no no.  At first I thought maybe I had  broken mixture cable.

When I got enough altitude, I pumped the throttle from wot to closed and back to wot and the engine cleared and EGT went back to normal.  The rest of the flight was normal. I have about 30 SMOH, and have never run anything but 100LL..  In the summer, in Texas, I usually leave my cowl flaps open unless I get up high and cool.  I can only guess I was maybe a little vapor locked.  Anyone else have a similar experience?

And what was the DA of the field?   I got 3000 DA at Brenham today which is a 300 foot field.   Did you do a lean run up or just shove the mixture full forward?   Last year at Midland I shoved everything forward for a quick departure.    Not a good idea  DA was 5000.  Do you aggressively lean on taxi?

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You may have a failing mag. I had the same EGT indication 7 years ago when the mag was failing on my m20f: intermittent high EGT. 

Buy once. Cry once. Get an engine monitor. 

I had an engine failure on takeoff at 200ft after getting mine. The peace of mind it gave me knowing that there was no warning, compared to including it in the potential “what ifs”, especially had it resulted in life changing results was worth it alone. 

My engine monitor also alerted me to when my engine had spun a main bearing and I would’ve not noticed the intermittent drop in oil pressure otherwise. The shop that did the overhaul said it was one of the worst engines they’d seen and suspected I was close to a catastrophic failure. 

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And for a FI engine running at 30PSI, I don't think a vapor lock is possible inflight.  There is too much cooling on the fuel lines and too much pressure.  On take off you are putting 20 gallons through those 4 little tubes.  Vapor lock is fuel boiling in the fuel lines.  You are clearing the vaporlock when you start.   possibly if your pumps are weak.   Now you may be sucking some air into the system.

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11 hours ago, Hank said:

I'd still check that. The Owners Manual for my C says 18.2 gph at sea level, WOT / 2700; I can't imagine that your J is happy with less fuel, since it's supposed to make 10% more power.

There's no spec for min FF at full power in the J POH (and I suspect it's not a spec in your C), and it's not field adjustable unlike in Lycomings, only idle FF.  If you think about it, 100% power should be had with 13.3 gph or so, although the motor will probably be very unhappy.  16.9 gph should be plenty of margin with the extra 3.5 gph or so rich of peak.  I end up about 300-350oF ROP at full rich at sea level, and CHT's don't exceed 370oF on hot days, so that seems about right.

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5 hours ago, Yetti said:

And for a FI engine running at 30PSI, I don't think a vapor lock is possible inflight.  There is too much cooling on the fuel lines and too much pressure.  On take off you are putting 20 gallons through those 4 little tubes.  Vapor lock is fuel boiling in the fuel lines.  You are clearing the vaporlock when you start.   possibly if your pumps are weak.   Now you may be sucking some air into the system.

Its possible. The lift line from the firewall to the mechanical pump inlet can get vapor. The mechanism is this, the line runs vertically, almost, from the bottom of the firewall to the mechanical pump inlet, it also passes close to the muffler.  Mechanical pumps push better than they pull. The fuel in the inlet line gets hot, then as its pulled upwards, vapor bubbles form. The hose is under suction, not pressure. the pump then passes this air and partially loses its prime. The hotter it is outside and the steeper you climb, and the higher you go, the more the fuel pressure dips.  Mine would get to 11 PSI.  Below around 15 PSI the engine would change tone and the EGTs would start fluctuating too.

  I got this when I replaced the fuel lines with 124J integral silicone fire sleeve hoses. They meet the design spec for fire rating but they transfer more heat to the fuel, because there is no slip-on fire sleeve over the hose. I installed the fire sleeve from the old hose OVER the new one, and fixed it.

 

Edited by jetdriven
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3 hours ago, jetdriven said:

ts possible. The lift line from the firewall to the mechanical pump inlet can get vapor. The mechanism is this, the line runs vertically, almost, from the bottom of the firewall to the mechanical pump inlet, it also passes close to the muffler.  Mechanical pumps push better than they pull. The fuel in the inlet line gets hot, then as its pulled upwards, vapor bubbles form. The hose is under suction, not pressure. the pump then passes this air and partially loses its prime. The hotter it is outside and the steeper you climb, and the higher you go, the more the fuel pressure dips.  Mine would get to 11 PSI.  Below around 15 PSI the engine would change tone and the EGTs would start fluctuating too.

  I got this when I replaced the fuel lines with 124J integral silicone fire sleeve hoses. They meet the design spec for fire rating but they transfer more heat to the fuel, because there is no slip-on fire sleeve over the hose. I installed the fire sleeve from the old hose OVER the new one, and fixed it.

 

I could see it.  For this situation I would still vote to over rich.   The interesting one to note would be to check the mech fuel pump cooling.   Is the shroud in place or is the air hose pointing at the pump.    I could see the Mechanical pump cavitating along with your issue of trying to suck fuel up from the gas collator.      Popping on the electric pump should fix the issue.

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2 minutes ago, Yetti said:

I could see it.  For this situation I would still vote to over rich.   The interesting one to note would be to check the mech fuel pump cooling.   Is the shroud in place or is the air hose pointing at the pump.    I could see the Mechanical pump cavitating along with your issue of trying to suck fuel up from the gas collator.      Popping on the electric pump should fix the issue.

I have to imagine, though, that the OP had the electrical fuel pump on since this was an issue during his takeoff?

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The pump doesnt cavitate, its a diaphragm.  But it can get air on the inlet side and then not pump as efficiently as it is supposed to.

Turning on the electric fuel pump fixes it, but its not fixed, its covered up.

He likely doesnt run the fuel pump in climb because a Dukes electric fuel pump is quite expensive, and not rated for continuous duty.  forgetting to turn the pump off can cost you 1500$.

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