Low Oil Pressure - measured with external gauge

[Coultl]

Ugh. Not what I wanted to find and would love any insights from the community.

On my 84' 911 the dash oil pressure gauge showed low oil pressure once fully warmed up at idle. Near zero. Felt likely to be a gauge issue as the engine has been well taken care of (140k miles but no varnish inside).

Got an external gauge, hooked it up, and got the exact same readings. Cold = 3 bar at startup. Fully warmed up = Near zero pressure at idle. Something like 2 psi maybe. 1 bar at 1k rpm, 2 bar at 2k rpm, 3 bar at 3k. Seems to stop rising at about 3.5 bar.

The oil pressure light has never come on. Oil and filter are new. Mahle filter. 20W-50 VR1 oil. No knocking or other unusual noises. No noticeable oil leaks. I cut the filter open on my last oil change and it was clean / no metal.

Anyone insights or ideas? Anyone had low oil pressure like this? Thanks in advance!

[Michael7810]

My 85 with 225K miles has the same OP as you stated both at idle and off idle. My light does not come on at idle but is on with engine off so it works. The manual says it’s OK for the light to come on at idle when the oil is hot. I’ve never tested with a direct reading gauge. I wonder if your direct reading gauge is accurate at low pressures. With the exception of you direct gauge readings, your OP looks normal to me.

[porschyard]

The oil pressure spec is 4.5 bar (65lbs) at 5k rpm, it was 5 bar at 5k rpm on earlier cars.
The idiot light is 1.5-4.5 psi. (0.1- 0.3 bar) I would make sure your oil pressure is 4.5 bar at 5k at operating temp then I would pull the bypass and oil pressure relief valves and see if there is anything in the seat keeping them from closing completely at low rpm.
Many years ago I saw a similar problem and it turned out a couple of the piston cooling jets were missing but by the time the motor was disassembled the main and rod brgs were also showing a lot of wear so that could have contributed to the low idle pressures.

Richard

[911obgyn]

I put oil line restictors on the cam lines and it improved my idle oil pressure. I would like to see opinions, no oil light flicker before at idle without them but the needle is not buried anymore. Makes me feel better.

[Michael7810]

Originally Posted by porschyard

The oil pressure spec is 4.5 bar (65lbs) at 5k rpm, it was 5 bar at 5k rpm on earlier cars.
The idiot light is 1.5-4.5 psi. (0.1- 0.3 bar) I would make sure your oil pressure is 4.5 bar at 5k at operating temp then I would pull the bypass and oil pressure relief valves and see if there is anything in the seat keeping them from closing completely at low rpm.
Many years ago I saw a similar problem and it turned out a couple of the piston cooling jets were missing but by the time the motor was disassembled the main and rod brgs were also showing a lot of wear so that could have contributed to the low idle pressures.

Richard

The owners manual for my '85 says at 5000 rpm the oil pressure should be at least 3.5 bar

[porschyard]

Originally Posted by Michael7810

The owners manual for my '85 says at 5000 rpm the oil pressure should be at least 3.5 bar

From the technical specifications book

[porschyard]

Spec for 83 and earlier cars

[porschyard]

3.5 bar would be a minimum pressure spec.

Richard

[Coultl]

Appreciate all the input on this one!

Agreed, the external gauge is probably not accurate at such low pressures, but it really seems like there's almost no pressure. I can press the relief valve on the oil gauge to let oil out and it barely comes out.

What I'm hearing is that oil pressure at idle just isn't that critical on this engine. I don't understand that, but hey, I'll take it for now. I do hit 3.5 bar at about 4k rpm but it doesn't really go up from there. Maybe hits 4 bar. I'll double check.

The oil light not coming on makes me think that maybe the oil pressure is also lower at this location.

I bought the cam oil restrictors (901-105-361-02) and I will report back on the change in oil pressure. Should have that done next week.

[Ian Comerford]

Over time lots of people have experienced very low oil pressure at tickover when hot and been concerned. It seems that with a used engine such as yours it is not unusual. The key detail is what it is doing as the revs rise and yours does not seem bad at all. Put the restrictors in, keep using good oil, change it regularly and enjoy your car.

[wazzz]

What I don't understand from your first post you say near zero pressure at idle and 1 bar at 1 k.
Assuming your idle is 800 rpm, does that mean that the oil pressure jumps from near zero to 1 bar in just only 200 rpm?

[Coultl]

Wazzz, that’s whats’s strange. The oil pressure builds in such a non-linear way. It’s not quite at 1 bar at 1k rpm but it’s easily at 2 bar at 2k rom. It also tops out at 3.5 bar when hot. When cold it tops out at 4.5 bar. Video with engine hot below.

I think I might have either an oil relief or safety valve issue. Here’s my panned sequence. Install cam restricters, test, new oil relief valve & spring, test, new oil safety valve & spring, test. Really don’t want to remove the header to get to the safety valve…

Video: https://youtu.be/Bg3nkYAc1ls?si=Xcs4Dy6ZntNHs91l

[Coultl]

Also, the above video is with a brand new Porsche pressure sensor installed. It’s more optimistic at idle than either the old sensor or the external gauge. Makes me feel better but who knows which one is actually the most accurate. Ha. All showed the same(ish) peak pressures.

[wazzz]

From your video, two things. Your 0 when engine is cut and ignition is on is a bit offset towards negative. Your idle rpm seems a bit low. If you account for these two factors, your oil pressure at real idle (800 for you I think) is not so bad. Probably still a bit under 1 bar, but that's correct IMO.

Don't know about the top 3.5. It could be better, but it is not that bad if you consider the negative offset of your dash instrument.

[Coultl]

Installed the cam oil line restrictors tonight and I have some results!

Not a bad job at all but I also don’t have the AC in the car. The left side requires you to remove the distributor. The rubber section of the right cam line was toast and had been seeping for a while. Replaced it with some high quality 5/16” fuel line. Strangely the other side looked perfect.

As for the outcome, there’s a clear increase in oil pressure. I’m seeing about 0.5 bar more at idle and a full bar more at 2k rpm. The peak pressure is still not hitting 4 bar but it’s a little improved from before. Videos below.

Next up I’m going to replace the oil pressure relief valve and spring. I’d be really surprised if there’s an issue there but it’s easy and cheap enough to do.

Before cam oil restrictors: https://youtu.be/Bg3nkYAc1ls?si=LdviCTjuyJl4oR_s
After cam oil restrictors: https://youtu.be/JyHZnbTW1IE?si=YFYYucPZqzK6mIXg

[Coultl]

And here are a few pics of the adapters. The one with slot cut out of it is the new one and that slot makes it easy to identify what’s in your car.

[wazzz]

It improved the idle pressure. Please note that your idle rpm is about 700, which is still a bit low and missing 100 rpm. As far as I remember the engine speed at rpm for your model year should be set to 800.
I took a screen cap from your first video before restrictors were installed, just at a moment when rpm climbed at 800. You can see that you have a good half bar showing on dash gauge. Accounting for the slight negative reading offset, that's almost 1 bar.

Second screen cap is from video after restrictor install. This time, captured again at 800 rpm, a good 1-bar pressure is showing on the gauge, which should be almost 1.5 real pressure when accounting for your negative offset. All good.
As for the higher engine speeds, it seems that the restrictors improve pressure at mid range too, but do nothing past 4000 rpm.
I checked my own car (88 Carrera) the other day at running temp (90°C) and reached 5 bars at 6000+ rpm... in 5th . Man that car is fast!
But my gauge is sometimes slightly offset in the + direction (as opposed to your negative offset), meaning what I see on the gauge is actually half a bar lower.

[proporsche]

as Gilles said your idle is too low..overall i am thinking you are using the restrictor as a band aid..i would really look for the low press cause....what oil are you using?

Ivan

[Coultl]

Thanks Gilles and Proporsche. The idle does look low on the tach. I will check. A couple weeks back I adjusted the idle screw per the correct procedure and used my timing light to get an exact RPM. It was dead on, but maybe something changed.

I believe the cam line oil restrictors are recommended by Porsche? I don’t love the idea of it, but I have to assume they had their reasons. Hopefully…

[proporsche]

Originally Posted by Coultl

Thanks Gilles and Proporsche. The idle does look low on the tach. I will check. A couple weeks back I adjusted the idle screw per the correct procedure and used my timing light to get an exact RPM. It was dead on, but maybe something changed.

I believe the cam line oil restrictors are recommended by Porsche? I don’t love the idea of it, but I have to assume they had their reasons. Hopefully…

here is some reading for you...
Oil line restrictors, good or bad idea?

Ivan