Mystery Penetration 1975 M20F

[mike_elliott]

34 minutes ago, Yetti said:

I am trying to get my head around.  How hot is it back there anyways.   If it is hot enough to boil fuel would the fuel lines outside the shroud not also boil fuel.   I would think the fuel injection lines sitting on top of the engine would boil fuel better until they are hit with pressurized fuel.  The shroud/hose assembly is only going to work while in flight or maybe a little air with the prop spinning in ground ops.  How hot is it back there?

Leaks.  There is a tell tale drain on the pump.  The pump housing would have to split or the diaphragm blow out the side.  Seems like a really, really remote chance.

My thinking would be if it were NOT an area of potential issue of reasonable probability occurrence, Mooney would not have put it on to begin with and raise their COG. Be careful not to rationalize not having it there. Most likely it was not re-installed because, as a lot of  lesser A$Ps have said "Mooneys are hard to work on".

It may be just to aid the life of the pump, as an afterthought, but it was eventually designed and included on the planes when new for a reason

[cnoe]

What model/years planes is this setup on? My '78 J has no baffle pass-thru, no scat, no pump shroud and I'm fairly certain it never did. Never had a vapor lock issue even in Texas summertime. Just wondering...

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[TTaylor]

17 hours ago, Marauder said:

I also have a tube that cools the vacuum pump. I need to take some pictures when I am doing oil changes. These questions come up a lot!

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I agree with Marauder, on the 75 it is for SCAT tube to the vacuum pump. 

[N601RX]

 

43 minutes ago, cnoe said:

 

What model/years planes is this setup on? My '78 J has no baffle pass-thru, no scat, no pump shroud and I'm fairly certain it never did. Never had a vapor lock issue even in Texas summertime. Just wondering...

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The J models don't have the fuel pump shroud, but they have the oil cooler airflow and some additional baffling above the fuel pump that the earlier models don't have.   The only time I have saw any indication of a problem is after landing with the engine hot and then having to set and idle for several minutes in warm weather.  After several minutes the fuel pressure became erratic and dropped. The boost pump would bring it back up as soon as it turned on.  Another concern that may not be immediately obvious may be shortened fuel pump life.

The vac pump shrouds that I have saw is an aftermarket item made by Tempest.

http://www.aircraftspruce.com/catalog/inpages/tempestShrouds.php

[N7186V]

From Frank at Mooney:

"Vince,

I have looked further into the Scat Tubing – This maybe your item: The one I sent earlier was on the lower baffle – This one is on the upper (P/N 600208-3 baffle)" (SEE PICTURE)

Added response:

"There is a reference “Note:  Route End of 640001-19 Duct, approximately 2 Inches from fuel pump directing air stream around pump.” "

 

The engineering doesn't show a shroud for my model.  I did reply to make sure that the tube is indeed loose and directed at the air pump only, but if there was supposed to be a shroud, I would expect to see it here.  I'll confirm his response.

 

I don't have the manuals for pre-1975 models, so I'm not sure if this is a change from earlier models.

 

Thanks all!

Edited January 21, 2016 by N7186V

[Yetti]

2 hours ago, mike_elliott said:

My thinking would be if it were NOT an area of potential issue of reasonable probability occurrence, Mooney would not have put it on to begin with and raise their COG. Be careful not to rationalize not having it there. Most likely it was not re-installed because, as a lot of  lesser A$Ps have said "Mooneys are hard to work on".

It may be just to aid the life of the pump, as an afterthought, but it was eventually designed and included on the planes when new for a reason

No rationalization.  I want to keep beating the horse till I get the correct answer.  There was lots of things not done properly with this plane over the years.   For a plane(75F) with a undocumented electric landing gear and a TDS max rpm that does not match the propeller or the engine.  I think we are all here to learn.   And the drawing above helps us all learn.   I am also wondering if the earlier fuel pumps were not dual diaphragm without the tell tale so that made the shroud more necessary.

Luckily there is an oil change in the near future looks like I will be rerouting some tubing.

[Guitarmaster]

From Frank at Mooney:

"Vince,

I have looked further into the Scat Tubing – This maybe your item: The one I sent earlier was on the lower baffle – This one is on the upper (P/N 600208-3 baffle)" (SEE PICTURE)

Added response:

"There is a reference “Note:  Route End of 640001-19 Duct, approximately 2 Inches from fuel pump directing air stream around pump.” "

 

The engineering doesn't show a shroud for my model.  I did reply to make sure that the tube is indeed loose and directed at the air pump only, but if there was supposed to be a shroud, I would expect to see it here.  I'll confirm his response.

 

I don't have the manuals for pre-1975 models, so I'm not sure if this is a change from earlier models.

 

Thanks all!

That is exactly what mine looks like!

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[Guest]

Most airplanes have a cooling shroud on the fuel pump.  The manufacturer must have had sound reason for installing it.  If yours is missing it is not as designed.  

Clarence 

[Shadrach]

9 hours ago, Yetti said:

The boiling point of 100LL is 170 C.  Is it at or near 170 C hot?

The initial boiling point of Avgas is 25-170C or 77-338F. The number changes temp and pressure. Vapor lock is real. It may not be a huge risk in a 4cyl Mooney, but it happens.