REFLECTOR: Oil temps

[Chuck Jensen]

Al,
 
Good explanation.  Hard to believe but I could actually get my head
around the thermodynamic explanation.  Perhaps the higher oil temp is a
combination of the two; higher horse power as Scott surmised and greater
oil flow as John postulated.  Even though the amount of heat rejected by
the oil cooler is higher with higher oil flow, a temp sensor downstream
of the oil cooler may still be hotter with the higher oil flow at higher
rpm.  As always, everything is related to everything.
 
Chuck Jensen 
 
 -----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Al Gietzen
Sent: Monday, May 28, 2007 6:49 PM
To: 'Velocity Aircraft Owners and Builders list'
Subject: REFLECTOR: Oil temps



 

 

I see higher oil temps at higher rpms also.  I think the reason is that
the oil pump is a positive displacement pump which means the amount of
oil pumped is proportional to rpm.  The cooler can not cool a greater
flow down to the same temp as a lower flow. 

John 
SERG/Franklin 

Other things being equal; higher flow results in a higher heat rejection
capability.  It decreases the fluid side temp drop, which increases the
average temperature, and if the air temp is the same; increases the
average delta T from fluid to air, increasing the heat rejection.  I
know; it may seem counterintuitive, but the thermodynamics works that
way.  

The increased rpm increases the hp a bit, and would increase the oil
temp.

Al

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