REFLECTOR: Franklin Oil temp and flow data

Grover McNair grover at mcnairperformance.com
Mon Nov 11 09:57:36 CST 2013


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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