O-360 manifold pressure goes to 30?

[Craig-Bearhawk]

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?

 

[Briar Rabbit]

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?

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

 

[SkyDog58]

A leak that vents to ambient would make it jump to around 30.

 

[Salty]

30 seems a little high for a leak to cause unless you're awfully low

 

[Briar Rabbit]

30 seems a little high for a leak to cause unless you're awfully low

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

 

[denverpilot]

What altitude?

 

[BiffJ]

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

 

[Craig-Bearhawk]

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

 

[JAWS]

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

 

[Dan Thomas]

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

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.

 

[Dan Thomas]

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?

Is this a glass panel, or steam gauges?

 

[Craig-Bearhawk]

All analog gauges, it’s s stripped Down Bush plane

 

[Salty]

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

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

 

[Dan Thomas]

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

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

 

[Paulie]

You have a leak in the line or gauge.

 

[Pat Elliott]

The manifold pressure is taken off the manifold,..

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

 

[Paulie]

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

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.