Oil Pressure Question

[Tspringer]

I got my '69 911S hotrod project running yesterday evening... first time in 10 months. Its going to need some tuning, but that was expected. The engine was out as the entire engine bay was stripped and painted and all the rear suspension was rebuilt.

I also installed a complete oil cooler system purchased from Elephant. Chuck was really great working with me on install and some custom fittings for my car. I had the oil tank out for cleaning and painting, so the entire oil system was expanded and had been dry.

The car has me worried on oil pressure. Before I began this project, the oil pressure was on spec at 10lb per 1000 rpm or so. When hot (less than 210 degrees) under hard acceleration to 7000rpm it would show a maximum pressure of about 70lb. When in a constant state cruise on the highway at 3500rpm, it would show perhaps 30lb or slightly less. Now when I ran it yesterday, the pressure was low. Usually when cold, the pressure at 1500rpm would be close to 60lb. It was more like 20lb yesterday and fluxuated a good bit.

Im not panicked yet, as I expected some of this. The entire oil system was apart and tank removed. The filter is new, The oil lines, thermostat, cooler and everything was dry so it would take some time for oil to flow through everything and come up to full pressure. I just dont have any idea how long this should take or if any bleeding of air would be required in some way? I also have a small leak at the front cooler that I will track later today, perhaps that is contributing as well.

I only ran the car for about 5-10 minutes total and never above 3000rpm or so. The pressure was still fluxuating a good bit when I shut it down.

So.... how long should it take for the pressure to stabilize? Anything special needs to be done to help bleed out any air?


Thanks,

Terry

[yelcab1]

Don't panic yet!

As soon as your engine fires up, the oil pressure should be high when oil is cold and more viscous. When the engine warms up, the oil becomes more liquidy (less viscous) and oil pressure drops at a given RPM. So 20 psi at 1500 RPM with a cold engine is a little low. The fluctuating bit is somewhat puzzling too.

Slow down, take a breather, fix that leak at the front cooler. I never had to bleed any of my oil cooling system, it is normally open-ended anyway with the oil squriting at the cams and then free falling into the bottom of the case.

There is also an update with the cam oil fitting with some of the earlier engines to restrict the oil flow and increase the oil pressure. Did you do that?

[Grady Clay]

Terry,

Is it possible you don't have enough oil? When starting from scratch, you have to fill all that plumbing. Fluctuating oil pressure is a common symptom of picking up air in the tank. Whenever in doubt, use a machanical gauge. It may be an instrument/ground problem.

Best,
Grady

[Tspringer]

I did add oil, and it helped a bit. The pressure was fluxuating but never dropping to zero or anything like that. I do have the updated oil fitting installed at the heads with the smaller orifice.

When I run it next, I will continue to add oil until the level is correct and I am sure the system is properly full. I also have a mechanical guage I can put on it. Last summer when I tested with the mechanical guage it showed the stock guage as accurate. Still, lots of electrical stuff has been apart so its worth testing again.

Terry

[Early_S_Man]

Terry,

All of the 'dry' lines to external thermostat, and front cooler are irrelevant to main oil pressure, as all of the above are in the scavenge circuit. The main pressure pump has a full tank of oil supplied via the 'S' hose as soon as you fill the tank, so oil pressure buildup is less than two seconds after startup.

Two possible problem areas ... sender sticking, or bypass/safety valves sticking or binding.

I suggest checking for both possibilities ... before running the engine again.

The sender can be checked by removing from the engine and slipping the M10 x 1.00 threads into a 3/8" rubber air hose and clamping in place with a worm-gear clamp ... and monitor resistance as you dial-up an air regulator in 10 psi increments up to 100 psi or so. I don't have the specific resistance measurements through the pressure range, but the 'at rest' value is in the 15 Ohm to 20 Ohm range. Any sticking should be obvious when the resistance stops rising with pressure.

Removal of the bypass/safety relief pistons requires a special tool be fabricated ... I ground down a Thorsen #574 'Drag Link Bit' to fit VW relief piston plugs decades ago and the Porsche 911 engines prior to SCs use the same size slot in their plugs. The tool is the equivalent of a GIANT slotted screwdriver bit ... about 0.1" thick, and 1"wide at the tip, and the fit in the slot needs to be very precxise and tight ... no slack or looseness. It needs to be 1/2" drive ... because it takes a lot of force to compress the springs for installation, and a very firm grip on a 6" impact 1/2" extension to control the plug and spring on removal.

The relief valve pistons usually fall out after the plug and spring have been removed ... within a minute or so. If stuck in place ... it may take some work with a tap or wooden dowel to get the piston out!

[fintstone]

Try removing the lead from your sender and cleaning the connection a bit of emory cloth or similar.

[Tspringer]

Warren,

Thanks for the tip. Any chance you have a pic of the tool you made? Also, does removal of the bypass/relief valves require any other disassembly or are they directly accessible from below? When they are out, is there anything special that should be done that could help increase oil pressure? I do want to test these things before running it again, and I have plenty of time since the front suspension is coming apart again.

Terry

[Early_S_Man]

Terry,

The two springs should measure 70.0 mm in length, relaxed. I have seen them as short as 68.0 mm, and would recommend replacement. With early heat exchangers ... access is fairly easy.





Here are a couple of pics that may make it more clear. You may want to update to the later 86 mm spring and guide, but you don't want to change pistons ... unless the bypass mod described in this thread had been done.

oilpump modification

[Tspringer]

Warren,

Thanks for the pic. Ill see about making a good tool for this. My car has SSI heat exchangers... at a glance it would seem at least one of them will have to be removed. Oh well.... I had it off a couple of months ago so it shouldnt be too terrible.

My engine was built by Henry Schmidt at Supertec. It was based on a 7R case from a '77 911S. I have do not know what if any mods were done relative to oil bypass. Any good way to tell?

If updating to the 86mm springs will get more oil pressure.... I want to do it! I need this engine to be good for another year or so at least. I dream of building a super trick twin plug 2.8 RSR style motor. I have another 7R case core motor and complete MFI setup set aside for this. The plan was to slowly build the new engine, at my leasure so I can learn as I go and make sure everything is perfect. The 2.7RS engine in the car only has about 20K miles on it.


Terry

[fintstone]

Just call or email Henry...he would know about the mod and would probably have the "build sheet"...but if he built the motor, I am sure the oil bypass mod was done. He doesn't miss much.

Is it at all possible you have hooked up your new "custom" oil lines incorrectly?

Since you have not had the motor apart the problem is most likely electrical...probably the connection at the sender or a bad sender. Does the needle fluctuate slowly and linearly or rapidly?

[Early_S_Man]

Terry,

A '77 case shouln't need the mod ... it should already be the updated case casting. You should already have the grooved ratrher than perforated relief pistons.

The 86 mm spring and guide tube wasn't intended to raise oil pressure ... it was to prevent binding in the bore. That is what MAY have happened to cause your low pressure situation!

Be sure to check and see if the plugs have slots or hex heads ... the latest updated plugs wouldn't need the special tool, and Henry may have already equipped your engine with them.
.

[Henry Schmidt]

Hi Terry
I have seen small pieces of gasket material travel through the engine and lodge under a piston. Check that first. If the engine was built by us within the last 15 years we would have used updated springs and pistons. One way to improve the oil pressure in early engines is to replace the cam feed oil fittings at the cam towers with fitting from a 91/92 Turbo. 901 105 361 01. This fitting restricts the oil flow to the heads. Porsche decided that 17 gal/ hr was too much so they restricted the flow to 12 gal/hr. This helps keep oil in your bottom end. They're cheap, try them.

[Tspringer]

Henry! nice to see you chime in. I was actually going to call you.

You did build the engine. I was just reviewing the build sheets. It was built for Mike Walker and completed apparently in Nov. of 2001 though they did not install it and have it running until the following spring. Mike then sold the car to William Woods who sold it to me almost immediatly in Sept. of '02. I drove the car sporadically for almost a year, but the suspension was weak and it needed further restoration, so in August of last year I started ripping it apart. It has probably had 10K - 15K miles put on it at most, perhaps less.

The only problem I have had with it was a very pronounced fuel in the oil issue. I noticed this when oil was being blown out the breather and it reeked of fuel. Apparently it was pushing that much fuel into the oil past the rings from running rich, or it had an injector leak. I have replaced all the injectors, and first on my to-do list relative to tuning when the car is back together is set the MFI to fix this problem.

The oil pressure has never been really great. I actually did call you and discussed this shortly after I bought the car, but since it ran incredibly strong (INCREDIBLY..... this is a FAST car) and the pressure, though at the low end of the scale, was within factory specs I just didnt worry about it. I did add the updated cam feed oil fittings and that did improve the pressure a little bit, but not very much. Maybe 5lb average at higher rpm, nothing noticable at idle. I tested with a mechanical guage. The car used to always show 70lb+ at 5000rpm or so when the oil was cool shortly after startup. This would drop to perhaps 60-65lb max under hard acceleration at 7000rpm when the oil was 200 degrees or so. I never revved over 5k until it was fully up to temp. At a steady state cruise on the highway at 3500 - 4000rpm the oil pressure would be stable at around 30lb or so. It would jump with acceleration.

I will remove the springs and pistons this weekend and clean everything up and check for any gasket junk or other problems. I hope its just that simple.

I am also thinking it could be that I just didnt have enough oil in the car. The system was bare, and I added 7 quarts before starting the car. Then after startup as the pressure was fluxuating rapidly between 25-30lb and 10lb or so I shut it down and added 3 more quarts. The problem was still apparent on the guage but perhaps not as bad? Hard to say now. After speaking with Chuck Moreland on the phone some today, It would appear that with the front cooler and plumbing the entire system may need another 3 or even 4 quarts to be full.

At this point my plan is to drain all the oil, fix the minor leak at the cooler (Chuck helped me identify that.... minor issue), remove and inspect/clean the bypass valves/springs/pistons, reassemble everything, fill with 10 quarts of oil and fire it up.

If after that I still have low oil pressure.... I dont even want to think about that.

Thanks again for the help.


Terry

[Early_S_Man]

Terry,

That's low all right ... maybe 2 qts too low, so that may be your only problem. Add 2 qts and see if the pressure returns to normal.

[Tspringer]

Will do Warren. Check your PM's, sent you a couple of questions.


Terry

[Vintage911Racer]

NOT ENOUGH OIL.............