REFLECTOR: Cylinder repair followup

[Al Gietzen]

John;

 

For the same 'average' temperature of the oil cooler; the lower temperature
drop across the cooler is increasing the outlet temp; but reducing the inlet
temp. Of course to really know what's going on we need more data than just
one temperature.

 

Perhaps a key point based on what we think we know, is that the 'average'
oil temp seen by the engine is lower - maybe very little, but lower.  That;
combined with higher flow, I would surmise, could only be a good thing for
the engine.  Higher flow will reduce the average bearing surface temp by
moving more oil through, which is a key factor.

 

Don't get too focused on the temp that you are measuring at one particular
point in the system. In the extreme you could reduce the flow until the
engine was being damaged, and your measured cooler outlet temp could be
comfortably away from the red-line temperature.  One view of what you are
seeing is that it suggests looking at ways to increase air flow to the
cooler, or consider a larger cooler. 

 

I don't know what the criteria or margins are built into the 'red-line'
temperature.  It's a function of the oil you are using.  If it is a good
synthetic, you could bump the limit up a few degrees if it makes you more
comfortable (but I would never actually suggest you do that).

 

Al 

 

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of John Dibble
Sent: Monday, June 29, 2009 9:25 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Cylinder repair followup

 

Al, that makes perfect sense and I have been thinking that all along.
Basically, the hotter the oil leaving the cooler, the more heat is being
removed.  In that sense, hotter is better.  But the fact remains that with
an OAT of 86 F, the oil leaving the cooler was 107 C, right near red line
and the oil entering the cooler must have been hotter.  I recall flying 2
years ago with a similar OAT and seeing an oil temp around 95 C.   I think
what is happening is that I am now removing more heat via the oil cooler,
heat which otherwise would be removed via the engine cooling air.  For sure,
if the oil flow is reduced, the temp will be lower.  I'm just struggling to
decide which senario is best for engine operation.  Seems like lower temp is
better. 

John 

Al Gietzen wrote: 

  

The increased flow will reduce the delta T, the change across the cooler
(and correspondingly in/out of the engine).  Depending on other factors, for
the same air flow, the amount of heat removal would be about the same or a
higher, so the average oil temp would be a bit lower.  However; with the
heat removal air flow limited the measured oil temp out of the cooler could
be a bit higher; while the temp in (out of the engine) would be lower.  Make
sense? 

Al

 





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