1976 Oil Pressure

[hank911]

So my new to me 76 seems to have low oil pressure after warmup.
I'm running BP 20/50 in the car.
On cold startup my gauge shows around 35 psi at idle and up towards 60@3500 rpm.
Once it gets warm the idle pressure drops to 10 or a little under and 3k rpm yields around 30psi.
The car pulls strong through 5k rpm.
I'm going to try a mechanical gauge to verify the pressure this weekend.
Am I correct I. Thinking I should see st least 20 psi around idle?
Seems like all my 3.0s ran more pressure at idle and at running rpms
If I'm not dealing with a sender issue, what are some other common reasons that it could be dropping off as it warms up?

Thanks

[john walker's workshop]

If the hot idle is 1000, you should have about 1bar pressure and 3bar @ 3000. A 76 with a lot of miles could show what you have now. There are cam tower oil line restrictor fittings that could raise the pressure in your bottom end.

[Targalid]

Cam oil line restrictors are recommended for our cars in a Porsche service bulletin. If you are below 3.8 bar your piston oilers will not help cool the pistons. The engine actually runs cooler with these oil line restrictors. Here is Peter Zimmerman's how to:
How-To: Replacing a 911 Cam Oil Line Adaptor - Porsche Wiki

[faapgar]

Hi,a very common issue with miles is leaking oil between the main bearing webs from wear.Have both case halves resurfaced and a line hone.Another area often overlooked is the cam tower bores lose their line hone from broken head studs and there is additional clearance between the cam bearing surface and cam tower bore.The line bore is not round anymore hence a leak of pressure.Fred

[Mark Salvetti]

Originally Posted by Targalid

Cam oil line restrictors are recommended for our cars in a Porsche service bulletin. If you are below 3.8 bar your piston oilers will not help cool the pistons. The engine actually runs cooler with these oil line restrictors. Here is Peter Zimmerman's how to:
How-To: Replacing a 911 Cam Oil Line Adaptor - Porsche Wiki

I seem to remember some years ago a debate about this mod. It increases oil pressure, but at the expense of oil flow to the cams.

Is consensus still that this is the way to go?

Mark

[hank911]

Forgot to add that the car has 140k on it with a documented rebuild by Redline in Los Angeles about 55k miles ago.
Has Carrera tensioner and runs pretty cool ( front cooler & thermostat) at about 190 on a 85-90 degree day, running it like a Porsche

[Targalid]

Mark,
True. The oiling of the cams is less, raising the pressure elsewhere in the engine. The wisdom at the time said that the cams were so heavily oiled that some reduction did no harm. Cams turn at half speed versus the crank. I did this modification a few years ago and saw a large increase in oil pressure. I also noticed a drop in engine temperature. Peter Z comments on these observations in his wiki. The OP may already have this upgrade since he had a full rebuild with carrera tensioners though his reported oil pressure suggests that he does not have the cam oil line restrictors. They are easy to install, cheap and easily reversed if he does not like them.

[Mark Salvetti]

Thanks, I don't have them either, but was planning to do a bit more research and probably install them.

Mark

[hank911]

Here's a couple shots of the current set-up.

[faapgar]

Hi,I apologise for my doom & gloom forecast for your motor.By the looks of your sender for your gauge it looks like a 3.2 unit which is not compatible to your 2.7 gauges.Usually reads about about 30% less.So the guys from Redline did a good job.Ciao Fred

[faapgar]

Hi,the oil temp sender looks correct.If it was a silver color it would read a different inaccurate value.But it is a brass color so different value.Ciao Fred

[Rawknees'Turbo]

Originally Posted by Targalid

Mark,
I did this modification a few years ago and saw a large increase in oil pressure. I also noticed a drop in engine temperature.

I wonder if the drop in observed oil temperature (am assuming that is what you are referring to by "engine temperature") is the result of less heat being removed from the cams via the oil, and thus lower oil temperature (would not be a desirable situation, if so)?

[faapgar]

Hi,just.one more thing.The Carrera tensioners do drop your oil pressure about 3-5 lbs.On an early motor this can trip the O.P warning light on at idle.I have a bag of around 800 of the pins for the pressure fed tensioners.Free to the 1st artist that will do something creative with them.Fred

[faapgar]

Carbon fiber kneepads reduce your friction temp when you are on your knees.Yeah whatever my name is.

[Rawknees'Turbo]

Originally Posted by faapgar

Carbon fiber kneepads reduce your friction temp when you are on your knees.Yeah whatever my name is.

Faaptabulous Fred, I read that as an endorsement based upon your extensive experience - thank you for the tip (just the), my friend!

[Flat6pac]

The 2.7 gauge sender is supposed to be a 0-10 bar unit. Imprinted along the base of the sender on the flats.
As far as restrictors, I'd rather waste a cam than a crank. As a general rule for me, I open the hole to 5/64.
Bruce

[gomezoneill]

Try replacing your oil pressure relief springs and pistons. Cheap and easy worth a try. They most likely not replaced when the engine was rebuilt. There are two pistons and two springs.

[hank911]

So I installed the oil-line restrictors today and happy with the results.
Before at idle my indicator was just a hair above the "0".
Would have only taken 30 minutes if I didn't have the original air-pump!

[930cabman]

Our 75S has the opposite, when cold the indicated pressure is close to 140 psi. I have not checked with an actual mechanical gauge yet. Where does the pressure relief open?

[Mark Salvetti]

Originally Posted by Flat6pac

The 2.7 gauge sender is supposed to be a 0-10 bar unit. Imprinted along the base of the sender on the flats.
As far as restrictors, I'd rather waste a cam than a crank. As a general rule for me, I open the hole to 5/64.
Bruce

Bruce,

I thought the restrictors came with 2.5mm holes. Your 5/64 is only 2mm. You sure you don't go bigger than that, maybe 1/8" (3mm)?

Mark