Oil pressure on Franklin 90

[Tim Lunceford]

Hi everyone,  My daughters Cadet is powered with a Franklin 4ac-199.  It has 157 hours since MOH by Winfield Aviation in New York and runs really well.  The issue I am having is low oil pressure.  It shows 22 lbs at startup and increases to about 25 lbs as the throttle in increased.  As the temp. reaches 160 degrees it falls to about 18 lbs.  and stays there.   I have had the oil pan pulled and check the screen.  No debris of any kind.  Replaced the oil pump gears, plunger and spring.  Changed oil to Aeroshell W100 a little better but still under 22 lbs at idle.  I replaced the gauge prior to all of the above to make sure the gauge wasn't at fault.  I would like to hear from anyone that has similar issues and if they were able to cure them.   Thanks, Tim

[Culver Dreamer]

Hi Tim
I was having a read in the Franklin Operators Handbook. It sure looks like you have covered all the possible bases with the oil pump.
On page 11 it indicates the only other thing low oil pressure can be is excessive main bearing clearance.
I wonder if other Franklin engined Culver Cadets could comment on what their oil pressure is at start up and in cruise. Do you really get the 35-45 psi as the book states should be there?
Regards Mark

[JoeB]

My Franklin 90 registers just under 40 on the gauge when fully warmed up during cruise.

[Tim Lunceford]

Thanks for the input Joe.  Does your installation include an oil filter and/or oil cooler?  I have both on my engine and we are beginning to suspect that pressure is reading low because the oil pressure gauge pick up port where the oil returns to the engine is down stream of both. 

[JoeB]

Thanks for the input Joe.  Does your installation include an oil filter and/or oil cooler?  I have both on my engine and we are beginning to suspect that pressure is reading low because the oil pressure gauge pick up port where the oil returns to the engine is down stream of both.

No, I have no oil cooler or filter installed. 

[Tim Lunceford]

Thanks Joe.  We pulled the oil pump again and shimmed the plunger with two washers.  I am now showing 33 lbs. at idle.  I am now convinced that the low reading is due to the location of the oil pressure pick up port being place downstream of my oil cooler and filter.  I have ordered a couple of fitting so that I can cap off the oil distribution block and bypass the cooler and filter.  I will be able to read the pressure directly.   I expect it to read higher the 45 lbs.  If its does I will feel confident that the issue is resolved.