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Why does the oil filter add oil pressure ??

L

Larry DeCamp

Well Known Member
I just added a remote filter to my 320. the cold oil pressure (xc20-50 / 75F ambient) went from 100 at start to way past 100. There is a no cooler relief with the Vernatherm, just the main gally relief with shims ( not adjustment thread).

Is it safe for the engine to fly until the oil reaches 180F ( normal pressure is 90 ) ? I assume the extra pressure setting was always there on the relief valve but the resistance of the filter is greater than the old screen !

Comments appreciated.
 
Larry DeCamp said:
I just added a remote filter to my 320. the cold oil pressure (xc20-50 / 75F ambient) went from 100 at start to way past 100.
Click to expand...

Where are you tapping the system for the oil pressure transducer?

There is a no cooler relief with the Vernatherm, just the main galley relief with shims (not adjustment thread).
Click to expand...

When the oil is cold, the vernatherm is wide open, thus significantly reducing pressure in the supply side of the oil cooler circuit.

When the oil is hot, the vernatherm extends, closing the bypass port. All oil flow must pass through the cooler. However, even hot, if the cooler circuit should become blocked, the vernatherm spring provides pressure relief and a flow path.

 
Oil Filter

On this subject: I recently called Airwolf and asked their engineering guy how much of a restriction did a spin on oil filter present to oil flow. His reply was when using the Champion filter they specify it was minimal, like 1-2 psi pressure drop across filter. I've never tried to measure this (yet)but always thought it would be higher. The filter specified has internal bypass.

Don Broussard

RV 9 Rebuild in Progress
 
Thanks Dan!

The OP sensor port is the left side as we dicussed. As you suggested, the most accurate supply pressure is sensed on the right side and I will move it there. However, it appears the filter has added at least 15-20 psi with cool oil as pump shaft load. Since many engines have filters, I assume the unrevealed extra pressure on the system is not a problem. I will carry on and simply move the sensor port so the pressure reading is relevant to the Lycoming spec.
 
cajunwings said:
His reply was when using the Champion filter they specify it was minimal, like 1-2 psi pressure drop across filter.
Click to expand...

A pressure drop figure without specifying a temperature or viscosity is meaningless. And it changes as the filter gets dirty.

Larry DeCamp said:
However, it appears the filter has added at least 15-20 psi with cool oil as pump shaft load.
Click to expand...

Refresh my memory...what port are you using? You seem to be measuring pressure prior to the filter element.

Here's a handy viscosity vs temperature chart, courtesy Donaldson. Look in the change in viscosity between 70F and 180F.

 
Oil Pressure

Quite a few years ago Lycoming changed the max oil pressure limit(red line) from 100 to 115 psi. I believe the top of the green arc is still 90 so I like to see the cruise pressure a bit below 90. I do not like continued operation at low green numbers. I believe high green numbers are beneficial for valve lubrication.
 
cajunwings said:
On this subject: I recently called Airwolf and asked their engineering guy how much of a restriction did a spin on oil filter present to oil flow. His reply was when using the Champion filter they specify it was minimal, like 1-2 psi pressure drop across filter. I've never tried to measure this (yet)but always thought it would be higher. The filter specified has internal bypass.

Don Broussard

RV 9 Rebuild in Progress
Click to expand...

that 1-2 PSI is with warm oil. Filters don't do well with cold, high viscosity oil. This is one of the reasons you are discouraged from running your engine past 1000-1200 RPM with cold oil, especially straight weights. If you crank up the RPM's, the filter can't pass the cold oil and it exits via the bypass, sending any debris in suspension back into your system.

Larry
 
Larry DeCamp said:
I just added a remote filter to my 320. the cold oil pressure (xc20-50 / 75F ambient) went from 100 at start to way past 100. There is a no cooler relief with the Vernatherm, just the main gally relief with shims ( not adjustment thread).
Click to expand...

BTW, what sort of remote filter adapter did you use, and what filter did you put on it?
 
Answers to Dan

Late breaking news, I moved the sensor to the right side and get 80+ psi at 75F with xc2050 at start. The filter is a NAPA 1515 that Rocket Bob uses and appears comparable the ACS champion offering. I fabricated my own adaptor that includes OT senser and Vernatherm ( you saw the pic). This was because B&C would not clear the motor mount tube and Airwolfe looked heavy, so I machined one from 4" round stock. Hoses are TS Flights lines -8 and Jeggs filter bracket. Lyc specs are 55 to 95 psi. Will post if any anomolies are observed.
 
>I do not like continued operation at low green numbers. I believe high green numbers are beneficial for valve lubrication.

I would agree wholeheartedly. Any comments on high oil pressure robbing horsepower?
 
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