Bill Verburg

Here's the 993 oil system schematic

Mike J

Thanks Bill!

So all oil goes through both filters, the small one is key to make sure no crap from the tank gets into the engine, and the big one to make sure the oil in the tank stays clean.

SO if the small filter is slowing down the flow, or reducing the pressure, then the main bearings, cams, sprayers, lifters all will take a hit.

Which is why I change both filters on every change. :-)

Cheers,

Mike

No HTwo O

A little bit off topic, but what about using Mann/Mahle oil filters on 996/986 and 997/987?

Slow Guy

Thanks Bill, I have it but didn't have access to it when i posted the previous comment.
That makes me feel good that the oil pressure sensor is between the oil filter and the main bearings/cam lobes and not closer to the pump. On even the hottest days mine doesn't drop below about 2 - 2.5 bar at idle and by about 2,500 RPM is back up to 5 bar, so that's good.

Personally, since I don't have a turbo I haven't seen anything that would give me concern about using any of the 3 filters in my car. If I had a turbo that would be a different issue.

geolab

Logically yes, technically No
Bill remember the 7th grade practice experiment with the water hose
fully open, flow is at max.
obstruct outlet with thumb, pressure rises and you rinse the blonde...
The brain thinks the same amount of water is still flowing out, but its not

pressure inversely proportional to flow in engine
all given practices constant
More pleats= more flow = more cooling = less presuure
Less pleats= less flow = less cooling = more pressure

BobbyT

What a great thread! I'm still not understanding the function or benefit of the anti-drainback valve, considering where this filter is mounted on a 993. Could someone shed some light on this?

Slow Guy

George, what I was trying to say is since there is a set diameter pipe/tube directly after the oil filter then more flow through the filter should translate to more pressure in the pipe/tube.

It's been a long, long time since I did those experiments in school so you'll have to forgive me if I'm a little rusty on them.

geolab

Logically yes , technically no
the output of oil from pump considered the same in pressure and flow
restriction creates pressure, that is the basis.
pressure from pump out in oil galley is high,
pressure drops drastically in oil filter (less restriction)
for info, pressure relief valve in 993 oil filter opens at 2.2 bar
oil, post filter, with less pleats is more pressurized,
then the galleys following create more pressure, so pressure is multiplied.
regards

axl911

Owww. My head hurts.

hoggel

This is only true if you are measuring differential pressure across the filter.

If you are measuring pressure in the lines relative to the crankcase then more oil volume in the same area is more pressure. In the analogy to the 7th grade experiment, the filter would be kink in the middle of the length of hose. The outlet would be the orfices to the bearings and the pressure regulator. Less flow out the bearing orfices would mean more pressure in the system ... as you said above.

geolab

I must be wrong
But I went from the pavlov idea that you cannot augment volume in the same galley
And augmenting flow reduces pressure in hydraulics in any scenario.

XR4Tim

I agree. If I put a kink in my fuel line leading up to my fuel rail, my fuel rail pressure drops. If I put a kink in my fuel return line, my rail pressure increases.
So, if you the filter is decreasing flow, then you are only increasing pressure pre-filter.

BobbyT

Interesting that the small filter is now in its third iteration. During a 993 tech session held by Tony Callas in 2004, the topic of excessive smoking on startup of the 993 Turbo engine came up. Here is an excerpt from my notes taken at that session:

"Excessive smoking on start-up. Text from Porsche TSB: When performing an oil change on the 1996 911 Turbo involving change of the oil filters, it is important to install the correct oil filter. Installation of the wrong part number small oil filter may lead to a customer complaint of engine smokes when started cold". Use the following chart as a guide for oil filter replacement.
General Information:
Vehicle type Small Filter Large filter

911 Carrera 1995 993 107 203 00 993 207 201 01

911 Turbo 1996 993 107 203 02 993 207 201 01
NOTE : Once existing stock of the small oil filter, part number 993 107 203 00 is used up, only the small oil filter, part number 993 107 203 02 will be available."

Was the 02 filter when the anti-drainback valve was added? Is the small filter mounted in a different location on the Turbo engine, necessitating this valve? I still don't understand how the anti-drainback filter can have any effect on the NA engine...