High Oil Pressure

[billd]

At an autocross this weekend, my recently rebuilt 3.2L short stroke engine started to show high oil pressure. At temperature it idles at about 30psi, at 2000 rpm it is up to 60psi, and at 4000 rpm the 150psi gauge is pegged.

My first step, when I get some time, is to put another gauge on it to see if this problem is real. Assuming it is, what could it be? I find it hard to believe that both the pressure relief valve and the safety valve have simultaneously failed.

Any ideas?

[Eagledriver]

Most likely a failure of the pressure sender. What does it read with the ignition on but the motor not running?

-Andy

[billd]

Unfortunately it is not the sender or the gauge. I checked the gauge this evening with a known good mechanical pressure gauge and it matched almost exactly. The pressure goes well over 150psi.

[hcoles]

Bill,
strange, the only thing I can think of is the relief valve is hung up.
most people on here mention 1 bar per 1000rpm... this sort of matches your lower rpm readings...but at higher rpm's you go too high.

4k rpm should be around 4-5 bar = 60-75psi

do you have the updated cam line restrictors installed? this raises the pressure a bit.

[billd]

Hank,

I do have the cam oil line restrictors installed. I pulled the pistons and springs from both the relief and safety valves this evening. They look a bit scuffed but not enough to cause them to hang up. I'm going to replace the pistons and springs and see if I still have a problem.

----Bill

[cgarr]

What does the alum sleeves (case) look like that that the pistons slide in? Did they fall out or where they hard to get out? What case are these in?

[J P Stein]

The latest (old now) fix is a tubular support (with a foot)for the pressure relief valve which fits inside the spring......the spring had been known to get "cocked" in the bore causing the piston to get hung up. In your pic, I see some wear on the outside of one of the springs and no support.

[billd]

Originally Posted by cgarr

What does the alum sleeves (case) look like that that the pistons slide in? Did they fall out or where they hard to get out? What case are these in?

No sleeves as far as I can tell. The pistons both required some persuasion with a magnet to get out.

I really can't get a very good look at the bores in the case with the engine in the car (a 914-6).

[billd]

Originally Posted by J P Stein

The latest (old now) fix is a tubular support (with a foot)for the pressure relief valve which fits inside the spring......the spring had been known to get "cocked" in the bore causing the piston to get hung up. In your pic, I see some wear on the outside of one of the springs and no support.

Do you have a part number for this tubular spring support?

[J P Stein]

No, sorry, but someone here will have it.

[billd]

Originally Posted by cgarr

What case are these in?

The engine is built on an aluminum 1976 Carrera 3.0 case.

[hcoles]

Bill,
what these guys are saying makes sense... the piston is getting hung up and keeping the spring straight should help.. I hope you don't have any damage in the bores.
-h

[304065]

You should have a spring guide for the longer spring. 930 107 533 00

[billd]

Originally Posted by john_cramer

You should have a spring guide for the longer spring. 930 107 533 00

Thanks for the PN. A few quick questions.

1. Do I put these guides on both springs (relief and safety valves)?

2. I assume the flange goes against the cap, not against the piston, right?

3. The flange will make the spring slightly longer, slightly increasing the pressure at which the valve opens. I assume I should just ignore this. Right?

[J P Stein]

Something you may find useful....a very nice feature from our host.
Your parts are under the engine section, Illustration 101-10, parts 29 thru 32.
It takes a while to load.
While you're at it, the new improved cap screw is a hex head rather that that PITA slot head.

https://techinfo.porsche.com/techinfo/pdf/en/catalogues/E_911_83_KATALOG.pdf

[billd]

I verified that the pistons move freely in the bores by pulling them back and forth with a magnet.

I then replaced both pistons and both springs.

There is no change in behavior. The engine still idles at 30psi and pegs the gauge at mid rpms.

Is it possible that my case (a 76 Carerra 3.0 case) does not have the oil bypass mod and hence needs the old style pistons? When exactly did Porsche switch over to the new system?

[hcoles]

Bill,
my car when cold has 2 bar at idle and pushes the inside gauge to the top when reved.
Then when hot I have a bit above 1 bar at idle and goes up from there maybe 1 bar per 1000rpm until hitting about 4 bar.
do you have the correct pistons/springs in each hole? Did you put the spring guide tubes on?
maybe if the springs are different you have mistakenly switched springs. I'm thinking that if no spring guide tubes the springs bind against the bores.

[hcoles]

I looked back at your picture... looks like both pistons and both springs are the same.
Did you always have this issue?

[cgarr]

If this case does not have the bypass mod then you are using the wrong pistons and it will run huge pressure.

[billd]

Originally Posted by hcoles

I looked back at your picture... looks like both pistons and both springs are the same.
Did you always have this issue?

I have had this issue since I acquired this engine. I rebuilt the top end but did not split the case and did not open up the relief valves until now.

I only recently got the pressure gauge working and have all of two autocrosses on the engine since I've been able to monitor pressure.

The next thing I will try is swapping out the lower spring for the longer one with the lower spring rate.