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m20e manifold pressure gauge took a break while flying


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Hey while shooting approaches the manifold pressure gauge decided to stop working.  

if I remember correctly, I think it read somewhere between 15 and 20 inches and I was at 3000ft.

Engine kept running, prop kept spinning  but mani pressure wouldn't move.

on the way back to the airport,  at approx. 2500 to 2000 ft the gauge decided it wanted to work again. wth?

landed,  taxied to the ramp for a runup,  everything seemed fine.

called my IA,  he didn't seem worried, at all.

 

anyone had this happen?  am I good?

Edited by McMooney
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The line has a couple of ways to fail...

1) At the engine end, it is open to evaporating fuel and deposited blue goo...

2) the goo has a tendency to get as far as the calibrated weep hole... follow advice from Clarence above... ^^^^

3) if you have an old Mooney, your MP line is about a 1/8” diameter, soft aluminum line, the calibrated weep hole is about 2” from the back of the MP instrument... the same line turns into copper on the other side of the firewall...

4) The calibrated weep hole has a tendency to crack, propagate and break... but before it breaks it can give the image of working properly, or opening up and failing... then closing up and working again, then cracking in half one day to never work again... vibration is tough on the long, and often unsupported, line.

5) Did I mention calibrated weep hole..? That’s a near secret, hidden in plain sight.... in the parts manual for one particular model... 

PP thoughts only, an old M20C lesson direct from Bill Wheat... Let us know if you need calibrated weep hole dimension...

Best regards,

-a-

 

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18 hours ago, M20Doc said:

I would open the manifold pressure line at the gauge and the engine flush and blow the line out.  

Clarence

Or check to see if the line broke at say maybe one of the connections.   Reflare the end and retighten.

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The little Flare fittings in the bnut between engine and firewall kept cracking, so I went to a flexible hose instead of the tiny aluminum tube. No problems since then. I think it’s a #2 size

Edited by Browncbr1
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As my engine only sees WOT or closing for decent and landing I really have no use for MP :-)

You can fly without it very easy by just going to high RPM and flying it like a fixed pitch prop. 

You won't harm it at all. 

BTW, "over square" won't really harm the engine either, within certain limits. Its even in Lycoming manuals if you look. Learned about it at MooneyMax this year, 

Lindbergh proved it in WWII on P-38s 

See what you miss by not attending?  :-) :-)

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Yes in my case aluminium tubing some how got split in it very subtle location. The manifold pressure gauge behaved like an altimeter when I  climbed to higher altitude. That's when I realized that I had a leak. 

I Do you  have aluminium tube going to your manifold pressure gauge? If so I suspect  you have a leak in the line some place, especially if you haven't replaced them in a while. They work harden become brittle and break easy.

James '67C

 

 

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On 6/16/2019 at 8:53 PM, M20Doc said:

I would open the manifold pressure line at the gauge and the engine flush and blow the line out.  

Clarence

This. I don't know why, but mine starts sticking and I have to crack open the line and blow it out every annual. A drop or two of oil-like substance clogs the line.

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