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04-05-2017, 10:29 AM
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Join Date: Oct 2006
Location: Garden City, Tx
Posts: 5,147
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The oil bypass relief that dumps excess oil back to the crankcase once it exceeds set pressure - is that routing before, or after the cooler? If most of the oil is bypassing right there it never sees the cooler, right?
__________________
Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2020 dues paid 
N16GN flying 700 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, 430W
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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04-05-2017, 11:44 AM
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Join Date: Sep 2011
Location: Edgewater, FL. KSFB
Posts: 1,118
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My initial thought on heat transfer is that the engine is a bucket holding x- heat.
The cooler subtracts heat. The combustion and friction add heat. If more heat is added than subtracted then is has less heat (cooler). If more is added than subtracted then more heat (hotter).
Unless a major amount of oil is by-passing the cooler and the cooler return oil is very cool then I would say no. the cooler is still removing x heat.
I would think that no matter the velocity or volume of oil flowing through the cooler then it will remove x heat. More or cooler air will change the amount of heat removed but the amount of oil will not.
The only other thing that could change the total amount of heat the cooler can remove (other than the mass airflow) would be the temperature delta/difference of the air vs oil temp.
I hope I wrote what I was thinking.
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04-05-2017, 12:21 PM
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Join Date: Jul 2005
Posts: 118
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Thanks for the feedback
After reading the feedback and studying the lycoming oil schematic I have a theory.
There is a constant quantity of oil going through the pump AND cooler at a given rpm. The cooled oil is either going to go through the galleys and hot parts of the engine or is going to be dumped back into the sump to recirculate. Setting the oil pressure relief value higher will cause more oil to flow to the hot parts of the engine before returning to the sump resulting in hotter oil in the sump. A lower oil pressure would cause more of the cooled oil to dump back into the sump resulting in a cooler sump temp. I could see a lower oil pressure resulting in a lower oil temp in the sump but higher oil temps in the engine where it actually matters.
Oil schematic found here:
http://www.vansairforce.com/communit...ad.php?t=45548
__________________
Todd Neidinger
RV-9 Flying
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04-05-2017, 01:04 PM
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Join Date: Sep 2011
Location: Edgewater, FL. KSFB
Posts: 1,118
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Quote:
Originally Posted by tsneidin
The cooled oil is either going to go through the galleys and hot parts of the engine or is going to be dumped back into the sump to recirculate.
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All the oil goes to the hot parts after the pump. None can bypass the hot parts.
It is possible to bypass the cooler but all the oil will go through the filter and then to hot parts.
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04-05-2017, 01:20 PM
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Join Date: Nov 2016
Location: Navarre, FL
Posts: 385
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Is there a kit we can install that will take the vernatherm completely out of the loop and push all of the oil through the cooler? I live in Florida so not too concerned with cold weather flying at this point
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04-05-2017, 01:52 PM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,298
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Quote:
Originally Posted by MarkW
All the oil goes to the hot parts after the pump. None can bypass the hot parts.
It is possible to bypass the cooler but all the oil will go through the filter and then to hot parts.
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This is incorrect, unless you meant that the sump is a "hot part." Right after the output of the oil pump, the oil reaches a control valve. This valve reduces the oil pressure from the pump (assuming it is actually higher - it should be). It does this reduction by dumping excess oil flow directly into the sump. Depending upon how much higher the pump output pressure is, relative to the pressure set in the valve, more oil will overflow to the sump. You can expect a considerable amount of oil is overflowing to the sump.
I would also argrue that most of the "hot parts" are actually not hot. The majority of the oil is flowing through the crank and cam bearings and the oil reduces most all friction there and therefore there is no more heat than the ambient internal case temp (the oil's job is not to reduce heat here, but to create a fluid surface for the journal to spin in, greatly reducing friction). Some of this oil flowing out of the crank bearings will be thrown on to the cylinder walls and pistons and cam lobes. That oil will pick up considerable heat, but that oil is the minority of the oil flowing through the system. Most oil goes straight to the sump at the same temp that it left the sump. This is why it takes so long to heat your oil up a low power settings.
This is why engines with oil squirters have higher oil temps or higher oil-based heat loads. They are sending more oil to the cylinders and therefore absorbing more heat into the oil. Without them, most of the heat is being transferred to the external air.
Larry
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N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
Last edited by lr172 : 04-05-2017 at 02:18 PM.
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04-05-2017, 02:00 PM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,298
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Quote:
Originally Posted by airguy
The oil bypass relief that dumps excess oil back to the crankcase once it exceeds set pressure - is that routing before, or after the cooler? If most of the oil is bypassing right there it never sees the cooler, right?
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Oil flows directly from the sump to the pump and then to the cooler (assuming vernatherm is closed and max pressure not exceeded.) then through filter and then to pressure relief (overflow to sump) then to galleries.
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
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04-05-2017, 03:17 PM
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Join Date: Sep 2011
Location: Edgewater, FL. KSFB
Posts: 1,118
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Oops, I looked at Dan's old drawing and missed the relief valve after the oil filter.
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04-06-2017, 05:49 AM
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Join Date: Apr 2006
Location: melbourne australia
Posts: 10
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Oil temps
Bret im not sure whether the oil pressure is in front of or behind the vernatherm but it did cross my mind that it may be lifting it.
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04-06-2017, 05:53 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by trifield
Bret im not sure whether the oil pressure is in front of or behind the vernatherm but it did cross my mind that it may be lifting it.
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DeltaP across the vernatherm = cooler pressure drop.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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