REFLECTOR: Franklin Oil temp and flow data

Mon Nov 11 11:12:53 CST 2013

 From my notes, and diagrams I made, my understanding of the system is 
that the bypass is there to ensure that the cooler is not over 
pressurized.  There are two regulators.
1) oil bypass, which causes a pressure differential across the cooler.
2) Galley bypass, which prevents overpressure on the engine.

The oil cooler will see an absolute pressure of galley pressure, plus 
cooler bypass pressure.  Absolute pressure does not imply oil flow.  
Only delta pressure across the ports to the cooler makes oil flow, and 
that's provided by the bypass.

If one looks at the bypass plate, you can see two spring loaded valves.

*    Increasing spring stiffness on the left valve sets the bypass 
pressure (delta pressure oil cooler) higher.
*    Increasing spring stiffness on the right side sets the max galley 
pressure higher.

The oil pump is a constant volume pump, not constant pressure. These 
valves are "relief" valves, meaning that above a setpoint, they will 
allow oil to bypass the circuit.  If the oil pressure is below the 
setpoint, then no oil is bypassed.  In other words, cranking up the 
spring pressure does not necessarily mean you get higher oil pressure.  
If the pump is only making 50PSI, setting the bypass at 80PSI is not 
going to get you more pressure.

That said, I do not know if the cooler bypass is bypassing.  If it is, 
then adding a stiffer spring there will cause more oil to flow to the 
cooler.

http://wiki.velocityoba.com/images/8/8e/Sevice_Letter_No_PZL-F_1_98_page_2_%28F6%29.jpg

On 11/11/2013 9:57 AM, Grover McNair wrote:
>
> Has anyone ever just bypassed the oil bypass valve to allow oil to 
> flow to the cooler constantly? I realize it would take longer to warm 
> and could potentially cause temps to be too low.
>
> Just curious.
>
> Grover McNair
>
> *McNair Performance Inc.*
>
> 6404 Westgate Rd.
>
> Raleigh, NC 27617
>
> 919-781-3604
>
> *From:*reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] 
> *On Behalf Of *John Dibble
> *Sent:* Monday, November 11, 2013 8:46 AM
> *To:* Velocity Aircraft Owners and Builders list
> *Subject:* Re: REFLECTOR: Franklin Oil temp and flow data
>
> On 11/10/2013 8:19 PM, Brian Michalk wrote:
>
>
>
>     It was about 70F today, not that cold.  The oil flow is just very
>     strange.  It didn't start flowing until nine minutes into the
>     flight, and I don't think it's a sensor problem because the
>     coolant temp leveled off after it started flowing.  If this data
>     is correct, I'm not getting enough oil through my cooler.  The
>     specs on the cooler are for 7gpm, and I'm barely half there.  Yes,
>     I'm having high oil temp problems.
>
>
> After my engine rebuild, my oil now takes 10 minutes to warm up.  It 
> used to take 4-6 minutes.  The reason for so much time is because when 
> the oil is cool, there is a high pressure drop across the 
> filter/cooler and nearly all the oil bypasses until the oil in the 
> sump, which warms faster, gets warm enough to reduce the pressure 
> drop.  The reason mine took less time before is because the bypass 
> spring was the wrong one.  It was the same as the oil pressure 
> regulating spring, which means there would be 80 psi across the 
> filter/cooler, before it would bypass.  That means the pressure off 
> the pump could get as high as 160 psig.  YIKES, but it ran without 
> incident for 1100 hours.  I couldn't get one of the special bypass 
> springs for the Franklin, so I made my own from a spring from the 
> hardware store that I calculated would give 20 psi pressure. My oil 
> runs 10 C cooler after the rebuild and I attribute most of that to new 
> bearings.  New bearings have a smaller space between the bearing and 
> crankshaft, so less oil passes through and therefore doesn't pick up 
> as much heat.  That reduces the oil cooling requirement.  Also, with 
> more oil now bypassing the cooler, there is less oil to cool and that 
> contributes to a lower oil temp (leaving the cooler) as well.  I 
> should point out that I have a larger oil cooler than the standard.  
> My CHTs are 10 C lower as well and I attribute that to the lower oil 
> temp.  My oil pressure runs 10 psig higher, also due to the lower oil 
> temp.  One trick I use to warm the oil with less idling is to runs for 
> 2 minutes, then shut down for 10-15 minutes.  When I start back up, 
> the oil warms up in 2 minutes.  This way my CHTs are still low.
>
> John
>
>
>
>
>
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