Oil Pressure at the filter

calling911 · 03:56 PM

I'm trying to figure out if my filter is going into bypass mode or not.. I use the standard Mahle filters which I SEEM to have discovered has a By-Pass Valve Setting of PSI: 18-22.

I was shocked initially.. but after looking at a oil diagram I see there are two pumps, one for pressure to the motor and one to scavenge.

So it looks like the pressure I see at the gauge in the car is not relevant to what is occurring at the filter.. I wonder if I have figured this right.. if I am right Im wondering if anyone knows what typical pressures are on that side when the oil is cold using 15w50 wt synth oil?

I have recently found really bad stuff in my oil tank.. and have also recently installed a oil cooler.. I do not want to be in bypass mode.. ever.. I was keeping my max pressure below 60psi thinking Id be safe.. but now i know, well, I know I just didnt know what I was doing is what I was doing.
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I know bearing failures dont seem very common so this is probably over-kill but I would like to try and limit the time Im in by pass mode..

Since 18-22 psi is really low, Im guessing the pressures above 180f are VERY low on that side of the system but I wonder if someone has some good data.

also, is the thermostat to the cooler analogous? In other words does it open slowly? My oil starts to gurgle to my cooler at 180f and I see all sorts of references that it doesnt open till 210f..

I did do some searching.. sorry if I missed a thread.

Joe Bob · Joe Bob's Garage

Using a hand held pyrometer and your on the oil lines hand will tell you what temp the external thermostat opens. Assuming you have a cooler in the wheel well.

Shooting the oil tank with the pyrometer will get results too....

DRACO A5OG · DRACO A5OG's Garage

Someone posted pics of a front oil cooler that they replaced new only to find debris and metal particals in it. Did you inspect the new oil cooler before install?

I recall, you need the by pass mode for cold starts. Some will confirm this.

calling911 · 05-10-2011, 04:31 AM

Quote:

Originally Posted by DRACO A5OG

Someone posted pics of a front oil cooler that they replaced new only to find debris and metal particals in it. Did you inspect the new oil cooler before install?

I recall, you need the by pass mode for cold starts. Some will confirm this.

That was me, and yes it was cleaned but I don't want to take a chance. I guess the only way to find out is going to be to install a gauge of some sort.

The other option will be to use a non- bypass filter which many feel are crappy just because of that fact..

calling911 · 05-10-2011, 04:33 AM

Quote:

Originally Posted by Joe Bob

Using a hand held pyrometer and your on the oil lines hand will tell you what temp the external thermostat opens. Assuming you have a cooler in the wheel well.

Shooting the oil tank with the pyrometer will get results too....

I guess my question was more about how much it opens, how fast... my thought is, at high PSI there is little to no oil flowing thru the cooler because the oil is cold.. so not a lot of worry about debris from the cooler getting to the engine right? Well, not necessary if the bypass opens at 18psi! But again, I dont know the pressure ON THAT SIDE.

Grady Clay · 05-10-2011, 04:40 AM

JP,

The pressure relief bypass valve in the oil filter operates on differential pressure (pressure difference) across the filter element and the valve in parallel.
I find a Porsche spec for the valve opening at 2.2 bar (~32 psi).
There are two situations where the valve opens: The first is when the filter element becomes restricted with dirt and debris filtered from the oil. Unlikely with proper maintenance.

The other is (I think) on start-up in extremely cold conditions. The oil has moved (by gravity) to the bottom of the engine. For the first few seconds, there is 100% oil being pumped by the scavenge pump (40% air normally). There is no safety pressure relief for the scavenge circuit in the engine.

The safety pressure relief valve integral with the external thermostat opens at about 120 psi (8 bar). This is the differential pressure across the front cooler and pipes and would only open during cold conditions and aggressive warm-up. This simply diverts the oil on to the filter.

Keep in mind that the ‘downstream’ (low pressure) side of the filter (element & valve) is at the oil tank and substantially at ambient atmospheric pressure.
In a 911 application, the filter sees little pressure.

You said: “I have recently found really bad stuff in my oil tank.”
Can you post a link?

You also said: “…have also recently installed a oil cooler ….”
What system? Is it a standard Factory system from ’74->’88?
Other?

Here is something I wrote on this subject yesterday:
question re oil flow engine vs tank

Best,
Grady

Grady Clay · 05-10-2011, 04:46 AM

Why don’t we rig an oil filter bypass valve with a switch that operates when the valve opens?
Collect data if/when the valve opens.
That will put this important subject to rest, once and forever.

Best,
Grady

calling911 · 05-10-2011, 04:48 AM

Quote:

Originally Posted by Grady Clay

JP,

The pressure relief bypass valve in the oil filter operates on differential pressure (pressure difference) across the filter element and the valve in parallel.
I find a Porsche spec for the valve opening at 2.2 bar (~32 psi).
There are two situations where the valve opens: The first is when the filter element becomes restricted with dirt and debris filtered from the oil. Unlikely with proper maintenance.

The other is (I think) on start-up in extremely cold conditions. The oil has moved (by gravity) to the bottom of the engine. For the first few seconds, there is 100% oil being pumped by the scavenge pump (40% air normally). There is no safety pressure relief for the scavenge circuit in the engine.

The safety pressure relief valve integral with the external thermostat opens at about 120 psi (8 bar). This is the differential pressure across the front cooler and pipes and would only open during cold conditions and aggressive warm-up. This simply diverts the oil on to the filter.

Keep in mind that the ‘downstream’ (low pressure) side of the filter (element & valve) is at the oil tank and substantially at ambient atmospheric pressure.
In a 911 application, the filter sees little pressure.

You said: “I have recently found really bad stuff in my oil tank.”
Can you post a link?

You also said: “…have also recently installed a oil cooler ….”
What system? Is it a standard Factory system from ’74->’88?
Other?

Here is something I wrote on this subject yesterday:
question re oil flow engine vs tank

Best,
Grady

I think I read what you wrote yesterday.. I guess I assumed what you just said here but when I saw the crazy low pressures that Mahle supposedly opens at I was shocked.. The Porsche spec you mention might be a Porsche spec.. but what about Mahle.. you will find posts on this board saying 18 psi.. but it was from WIX literature! So.... well...

I change my filter MANY times during the summer.. so what you say gives me some more confidence...

I also found debris in a brand new oil cooler I just installed.. it is a carrera reproduction from out host.. it was cleaned but I was told it could NEVER be cleaned 100%.. this is why the old design is no longer used.. the new coolers can be heated to 500f at the final stage and all debris is melted... not so with the old type which use brazing....

thanks.. and here is the link to the nastyness I found in my oil tank!
This cannot be good to find in my oil tank..

calling911 · 05-10-2011, 05:18 AM

Quote:

Originally Posted by Grady Clay

Why don’t we rig an oil filter bypass valve with a switch that operates when the valve opens?
Collect data if/when the valve opens.
That will put this important subject to rest, once and forever.

Best,
Grady

In looking at a mahle filter design.. I see a HUGE FLAW in Porsches design.. when the bypass opens.. the DIRTY SIDE of the filter is fully exposed to oil flow..

Its not wonder I found debris in the bottom of my tank.. Im sure it was from a former motor failure...

FWIW, I cleaned my oil tank out with mineral spirits.. the stuff I found in there was SHOCKING and fully exposed to the engine... luckily the oil tank has some safe areas for HEAVY and only HEAVY debris to land.. but go to a race track and all bets are OFF.

I'm sorry, but porsche screwed up... BUT I NEVER READ about bearing failures... so...

T77911S · 05-10-2011, 08:27 AM

here is some info on oil filters. it talks about the bypass valve and the anti drain back valve.

Motorcycle Oil Filters & Air Filters
Oil Filters Revealed - MiniMopar Resources

calling911 · 05-10-2011, 03:25 PM

Quote:

Originally Posted by T77911S

here is some info on oil filters. it talks about the bypass valve and the anti drain back valve.

Motorcycle Oil Filters & Air Filters
Oil Filters Revealed - MiniMopar Resources

Thanks.

Grady Clay · 05-10-2011, 05:53 PM

JP,

I agree.
The design is flawed.

What do we do about it?
Re-design the system properly with aftermarket (and Porsche) parts.
I would like to see more Pelicans contribute to and question my proposal.

Best,
Grady

calling911 · 05-10-2011, 06:04 PM

Quote:

Originally Posted by Grady Clay

JP,

I agree.
The design is flawed.

What do we do about it?
Re-design the system properly with aftermarket (and Porsche) parts.
I would like to see more Pelicans contribute to and question my proposal.

Best,
Grady

I have thought many times about installing a screen filter on the scavenge side.. I remember I used to use a moroso unit on a V8 based race car... Really not enough but something.. but the only other option would be to use a non bypass filter and watch your pressures very closely..

I read your ideas but Im no engineer.. and frankly Im even a little concerned about putting a screen filter on the scavenge side but I remember thats where they were on the race car and they worked fine... (had two lines on that car from the sump)... at oil change time would be simple to inspect...

I also feel pretty good about changing my filter way more often then needed.. its cheap insurance.. especially if bypass mode is mostly encountered when it gets dirty..

But again, how many bearing failures have you read about??? I've read about none... Which is interesting.. and I havent read about clogged oil galleys... have you?

If you look at the oil tank you will see that the very lowest parts of it are BELOW the hose output... which is where all my shrapnel was located.. it was lots of gritty metal and also the large pieces in the picture I posted..

If there are any engineer types on here, yeah Id like to see a discussion... I've had some mini discussions on here but the consensus was nothing on the scavenge side... you'd need positive pressure there.. so a small bilge type pump would work.. they make these for transmission coolers.. but you could NOT have a failure at that pump.... would be "bad".... I think...

calling911 · 05-10-2011, 06:12 PM

THis is what I think Im gonna do.. but in a -16... simple installation... and cheap.. oberg might be a better option.. but youd be surprised how much screen area there is in these moroso units.

calling911 · 05:51 AM

Here's another option.. this would stop debris in by pass mode.
Moroso 23845 Moroso Pre-Filter Oil Screen

and it would be on the positive pressure side...

Wonder if the dimensions would be right.. guess it fits a "small block chevy"... if it fits I think Im going to go this route..

EDIT: I think Im wrong.. this would not screen the output, only the input...

Grady Clay · 05-10-2011, 06:35 PM

Even the Porsche race department realized this problem with the earliest 6-cylinder race cars (in 904s).
There was a screen filter in the sump tank to prevent debris getting TO the pressure pump and there was a screen-type fine-filter (in place of the engine oil cooler) between the pressure pump and the engine lubrication.

Even the 917 (which has far more oiling requirements) had a HUGE screen filter at the outlet of the oil tank.

Guys,
Read this:
question re oil flow engine vs tank
Please criticize.

Best,
Grady

calling911 · 05-11-2011, 05:50 AM

I responded to your post in the other thread.. thanks for weighing in on this.. I thought I was the only one who thought this was a problem...

I think when you find metal in your oil tank you stop ignoring this oversight by Porsche.

Quote:

Originally Posted by Grady Clay

Even the Porsche race department realized this problem with the earliest 6-cylinder race cars (in 904s).
There was a screen filter in the sump tank to prevent debris getting TO the pressure pump and there was a screen-type fine-filter (in place of the engine oil cooler) between the pressure pump and the engine lubrication.

Even the 917 (which has far more oiling requirements) had a HUGE screen filter at the outlet of the oil tank.

Guys,
Read this:
question re oil flow engine vs tank
Please criticize.

Best,
Grady