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Fuel Pump Oil Seep

avrojockey

Well Known Member
Patron
This is a fairly new rebuilt low-pressure fuel pump with 200-250 hours on it. Fuel pressure is bang on desired carb inlet pressure of 3 psi. There is no leak from the vent so I assume the diaphragms are good.

However I have oil seeping from the right edge of the top diagram. I checked the torque on the screws and that one seemed loose, but I can't find the torque requirements. I know the torque for the bottom bolts are suppose to be 30 in-lbs but I can't find any reference for screws.

I'm assuming improper torque is why the oil is seeping here (oil is definitely coming from here and not anywhere else) but would like to know what the proper torque is.

Thanks! Tim

Note: pic below is not my pump but for reference
 

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This is a fairly new rebuilt low-pressure fuel pump with 200-250 hours on it. Fuel pressure is bang on desired carb inlet pressure of 3 psi. There is no leak from the vent so I assume the diaphragms are good.

However I have oil seeping from the right edge of the top diagram. I checked the torque on the screws and that one seemed loose, but I can't find the torque requirements. I know the torque for the bottom bolts are suppose to be 30 in/lbs but I can't find any reference for screws.

I'm assuming improper torque is why the oil is seeping here (oil is definitely coming from here and not anywhere else) but would like to know what the proper torque is.

Thanks! Tim

Note: pic below is not my pump but for reference

It is possible the the rubber was defective and hardened / shrunk in that spot. If that is the case, re-torquing may not resolve the leak.

Larry
 
It is possible the the rubber was defective and hardened / shrunk in that spot. If that is the case, re-torquing may not resolve the leak.

Larry

I tightened I little bit and it seemed to help. I don’t want to overtighten though so I’ll make a quick call to tempest or Lycoming to find out the torque on those top screws should be. Also it looks as though you make need to re-torque the bottom screws after the top as they look like they go all the way through

FWIW it looks like I have a Tempest overhauled pump as it has these fasteners...
 

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Lycoming says same as the bottom 30-45 in-lbs and if they're loose reapply Loctite 243 by backing out one fastener at a time, re-snug, and then re-torque in the usually crisscross pattern.

I'll report the results.
 
Yep...screws were definitely loose. Re-torqued as recommended and no oil seeping after 4.5 hours of flying
 
Update

Just a quick update if someone's search hits this thread...

The leak around the pump perimeter came back, and I'm 99% sure the leak was coming from the top "oil" diaphragm...the fiber reinforced one.

I decided to get a new pump to resolve and will post back with the results.

However, I disassembled the leaky pump to inspect the diaphragm and it looks like it's in great condition. I can't tell how/why oil is making its way outside :confused:
 
Just a quick update if someone's search hits this thread...

The leak around the pump perimeter came back, and I'm 99% sure the leak was coming from the top "oil" diaphragm...the fiber reinforced one.

I decided to get a new pump to resolve and will post back with the results.

However, I disassembled the leaky pump to inspect the diaphragm and it looks like it's in great condition. I can't tell how/why oil is making its way outside :confused:

Is it possible that it's not coming out there, but dripping from somewhere else? Oil under the cowl can do some really strange things...
 
Is it possible that it's not coming out there, but dripping from somewhere else? Oil under the cowl can do some really strange things...

I thought I had a pump leak like this, but it turned out to be 'drippage' from the oil filter change, since the filter is directly above it.
 
This seems to be a chronic problem. A couple of years ago I installed a brand new Lycoming I/O 390 and within the first 50 hours had the same problem with oil seeping from the upper gasket, enough to get the whole pump pretty wet. Nearly new pump, direct from Lycoming! Replaced the pump and got a refund from Lycoming. So, there is apparently a quality problem where those are made. I've been told they are now all made by Tempest.
 
Is it possible that it's not coming out there, but dripping from somewhere else? Oil under the cowl can do some really strange things...

Yea...I've been through that. I had a leaking thru-bolt on #2 and the oil was going as far forward as the alternator mount. I've have gone over every millimeter of the engine with thorough cleaning. There is just no other place it's coming from.

Even if I'm wrong, I'm glad I changed the pump. The A&P that changed the pump 2 years ago before I owned the airplane over-torqued the adapters and stripped the threads on the inlet and outlet of the pump. The torque was so high I had to stick the old pump in a vise and use a breaker bar to remove the adapters. Way over the 23-24 ft-lbs spec'd in the build manual or instructions that come with the pump.
 
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This seems to be a chronic problem. A couple of years ago I installed a brand new Lycoming I/O 390 and within the first 50 hours had the same problem with oil seeping from the upper gasket, enough to get the whole pump pretty wet. Nearly new pump, direct from Lycoming! Replaced the pump and got a refund from Lycoming. So, there is apparently a quality problem where those are made. I've been told they are now all made by Tempest.

Aero Accessories makes the Tempest brand...we will see how this pump goes. I bought a new one as ACS didn't have overhauled in stock and it was only $60 more.
 
Update...

New Tempest pump installed...clean and dry after a run and test flight. Fuel pressure seems less variable also. Still don't know why the other one was failing.
 
I have the same fuel pump oil seep on my I/O 390 with 375 hours. I too thought the oil was coming from somewhere else, but am now convinced its the pump itself. Is it likely that these small leaks will actually effect fuel pump pressure and fuel flow? After reading this thread, I am leaning toward just replacing the pump.

Thanks for posting this topic and any insight.:D

Greg Novotny
Tacoma Narrows
RV-14a N14ZP
375 hours
 
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