O-360 manifold pressure goes to 30?

Discussion in 'Maintenance Bay' started by Craig-Bearhawk, Nov 12, 2017.

  1. Craig-Bearhawk

    Craig-Bearhawk Filing Flight Plan

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    I have an O-360 with a constant speed prop and intermittently during a two hour flight I may see two to three times the manifold pressure quickly climb to 30 and then slowly come back down to where I had it at about 22. During this there’s no change in engine noise, RPM or power. The plane has about 110 hours on it from new. Anybody have any ideas?
     
  2. Briar Rabbit

    Briar Rabbit Pre-takeoff checklist

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    Probably a problem with the gage or an intermittent leak in the plumbing to the gage.
     
  3. SkyDog58

    SkyDog58 Final Approach

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    What goes here?
    A leak that vents to ambient would make it jump to around 30.
     
  4. Salty

    Salty Pattern Altitude

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    30 seems a little high for a leak to cause unless you're awfully low
     
  5. Briar Rabbit

    Briar Rabbit Pre-takeoff checklist

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    Wonder if it could be getting some compression from the airspeed resulting in higher displayed ambient pressure?
     
  6. denverpilot

    denverpilot Taxi to Parking

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    What altitude?
     
  7. BiffJ

    BiffJ Pre-takeoff checklist

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    could be a leaky intake valve bumping pressure in the manifold up too. Lots of possibilities so more specific info needed on when, how high, temps, rpm, manifold pressure setting, etc.

    Frank
     
  8. Craig-Bearhawk

    Craig-Bearhawk Filing Flight Plan

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    Altitude has been 1500 - 2500. Normal cruise 22- 23 squared, temps all in normal operating range.
     
  9. JAWS

    JAWS Pre-takeoff checklist

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    Check the connections and hose/tubing in the engine compartment. Should be a pressure cowl.
     
  10. Dan Thomas

    Dan Thomas En-Route

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    The manifold pressure is taken off the manifold, which is in the low-pressure section of the cowl, under the engine. The cooling air outlet puts that area at less than ambient.

    But a leaking line is most likely. Could be anywhere between the manifold and the gauge.

    It won't be a leaking intake valve. Any valve leaking enough to disturb the gauge would affect power output.
     
  11. Dan Thomas

    Dan Thomas En-Route

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    Is this a glass panel, or steam gauges?
     
  12. Craig-Bearhawk

    Craig-Bearhawk Filing Flight Plan

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    All analog gauges, it’s s stripped Down Bush plane
     
  13. Salty

    Salty Pattern Altitude

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    That's probably true. The pressure in the engine compartment is probably higher than ambient.
     
  14. Dan Thomas

    Dan Thomas En-Route

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    See post #10. There are two pressure zones in the cowl.
     
  15. Paulie

    Paulie Line Up and Wait

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    You have a leak in the line or gauge.
     
  16. Pat Elliott

    Pat Elliott Pre-Flight

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    on an O-360, it's usually taken off the #4 jugs primer port which opens to the intake just shy of the valve.

    in any case It's a loose fitting
     
  17. Paulie

    Paulie Line Up and Wait

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    Not always, I have a o360 that's plumbed to the bottom of the sump for manifold pressure. Don't get the pulses that the jug pickup causes.