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04-04-2017, 11:21 AM
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Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,597
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Quote:
Originally Posted by N941WR
Dan Correct me, if I'm mistaken...
By lowering the oil pressure, I believe you give the oil more time in the cooler, to transfer its heat to the moving mass of air.
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The oil pump is a positive displacement pump. So the pump output volume is for all practical aspects independent of system pressure (for our closed systems) and constant. I offer that since oil is not a prefect fluid the heat generated by the pumping action might add a marginal amount of heat at a slightly higher pressure - but I'd estimate the additional pumping heat between 65 and 75 psig would be hard to measure.
Oil cooler heat rejection is a function of pounds mass of air and air temp rise across the cooler. Bigger cooler - more heat transfer area and better airflow (pounds mass of air). Better cooler then higher air temp rise across the cooler. Better air pressure drop across the cooler (and everything else constant), more pounds mass of air.
Carl
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04-04-2017, 11:38 AM
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Join Date: Jan 2005
Location: SC
Posts: 12,887
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Quote:
Originally Posted by Carl Froehlich
The oil pump is a positive displacement pump. So the pump output volume is for all practical aspects independent of system pressure (for our closed systems) and constant. I offer that since oil is not a prefect fluid the heat generated by the pumping action might add a marginal amount of heat at a slightly higher pressure - but I'd estimate the additional pumping heat between 65 and 75 psig would be hard to measure.
Oil cooler heat rejection is a function of pounds mass of air and air temp rise across the cooler. Bigger cooler - more heat transfer area and better airflow (pounds mass of air). Better cooler then higher air temp rise across the cooler. Better air pressure drop across the cooler (and everything else constant), more pounds mass of air.
Carl
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Thanks Carl, everything I learned about this stuff in school many years ago, I have forgotten!
__________________
Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html
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04-04-2017, 11:54 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Quote:
Originally Posted by Carl Froehlich
The oil pump is a positive displacement pump. So the pump output volume is for all practical aspects independent of system pressure (for our closed systems) and constant. I offer that since oil is not a prefect fluid the heat generated by the pumping action might add a marginal amount of heat at a slightly higher pressure - but I'd estimate the additional pumping heat between 65 and 75 psig would be hard to measure.
Oil cooler heat rejection is a function of pounds mass of air and air temp rise across the cooler. Bigger cooler - more heat transfer area and better airflow (pounds mass of air). Better cooler then higher air temp rise across the cooler. Better air pressure drop across the cooler (and everything else constant), more pounds mass of air.
Carl
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The oil does collect air to about 5-8%. Right on the pressure, with that increase the pumping loss would be higher but with 95% efficiency already, marginal, and the total flow would also incrementally be lowered, although the various paths to the sump will change. Nothing jumps out as to why it would have such a pronounced effect on the oil temps. Unless a baffle seal was pushed back into place in the process.
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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04-04-2017, 07:13 PM
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Join Date: Nov 2016
Location: Navarre, FL
Posts: 385
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probes tested and all are fine. I got a chance to get it up and cruise around a bit today and the CHT's really came down. Still something going on but oil temps are steady around 195-200. It'll get me to SNF and back until I have more time to mess with the 4" scat tube to the cooler. Thanks to everyone for the help. Will post up more after I get a chance to mess with it some.
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04-04-2017, 07:58 PM
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Join Date: Sep 2015
Location: Nevada City Ca
Posts: 198
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It looks like the cooler is discharging towards the firewall? If so it needs turned down towards the bottom it will never work as well like it is
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04-05-2017, 05:26 AM
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Join Date: Apr 2006
Location: melbourne australia
Posts: 10
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Oil temps
Just for the record , I have an enclosed plenum, 4inch scat to 13 row cooler, 25' timing . As said previously nothing has changed the temps as dramatically as winding down the oil pressure. I would not have posted my results if it was possibly something else .
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04-05-2017, 06:03 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by trifield
Just for the record , I have an enclosed plenum, 4inch scat to 13 row cooler, 25' timing . As said previously nothing has changed the temps as dramatically as winding down the oil pressure. I would not have posted my results if it was possibly something else .
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I have a theory, something I've been kicking around a while. At s&f on a cell phone, more later
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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04-05-2017, 06:24 AM
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Join Date: Apr 2015
Location: Wee Waa Australia
Posts: 279
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You could try running your oil quantity a bit closer to minimums.
__________________
Kit 140241
Tail Feathers done
Fuselage kit completed.
wings almost complete.
Flaps and ailerons done.
Canopy next. Phew!
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04-05-2017, 09:54 AM
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Join Date: Sep 2011
Location: Edgewater, FL. KSFB
Posts: 1,118
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Quote:
Originally Posted by DanH
I have a theory, something I've been kicking around a while. At s&f on a cell phone, more later
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I got to hear this. See ya tomorrow.
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04-05-2017, 10:01 AM
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Join Date: Feb 2010
Location: Gardnerville Nv.
Posts: 2,828
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Could the higher oil pressure been fighting the spring on the vernathurm and therefor holding it off the seat allowing some oil bypass and not full direction to the cooler?
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7A Slider, EFII Angle 360, CS, SJ.
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