drv911

Problem: oil pressure builds and doesn’t stop. Cold pressure as high as 275 psi.

History:
’74 911
Updated oil pump and update kit, along with oil bypass mod to the case. Work done in ‘96
Long spring with guide pin and new type piston installed in the pressure relief valve.
Short spring and new type piston installed in the safety valve.

First off I’ve bought a oil pressure tester and tracked down an adapter to check pressure from the sending unit next to the fan, testing from the top of the square block. Tester is made by KD tools and is sold at Napa.

Problem: Pressure at cold start up at idle speed is a 125 psi and climbs with more rpm’s, 225 psi at around 2000 rmp and if I give a quick rev I see a reading of 275 psi. Once engine is at operating temp pressure at 3000 rpm is 60 psi.

What I’ve checked so far. Removed the cam oil line from the sending unit to cam tower, check for clog, no clog. Removed both upper valve covers and with coil wire removed crank the engine and get a good stream of oil from both spray bars. Removed the pressure relief valve, first time piston needed some help to get out, I used a fuel line that fit snug in piston to grab it and then it slid out. Reinstalled same piston, spring & guide pin, no change. Removed again, this time the piston slid out on it’s own after a few seconds, so it’s not sticking but I installed the old style short spring with a new piston (the new type of piston) and no change in reading. Have not looked at the safety valve yet.

The manual states the relief valve should open at 88 psi and the safety valve should open at 114 psi. Could a sticking safety valve cause this high pressure?
Even though the cam tower spray bar is spraying oil, does it sound like there may be a clog in the tower causing the pressure to backup?

At this point the car is parked until I find the problem. I’m posting this a two forums for better exposure.

Ed Hughes

Are you sure the gauge or sender isn't the problem?

drv911

Yes, Check paragraph 3

Steve Weiner-Rennsport Systems

I'll tell you that a real honest-to-God 275 psi will blow the engine mounted cooler pretty fast so my first suggestion would be to absolutely, positively make sure that your readings are accurate.

Don't assume anything: calibrate it.

drv911

I assume that when the dash gage and then a independent tester show the same results it should be accurate. Should I test the pressure from a different place? Should I have the KD tester checked?

Steve Weiner-Rennsport Systems

IMHO,....from experience,.....thats not a valid assumption.

The sender MUST match the guage and I've seen people make a lot of erroneous conclusions when the wrong sender is used with the car's guages.

drv911

OK. I have to ask this just to make sure we are on the same page. I've removed the sending unit from the square block and attached an adapter at this 18mm x 1.5 hole to test the pressure with a mechanical tester made by KD tools, readings are the same as with factory sending unit to dash gage as with the mechanical tester. Should I have the KD tools mechanical tester checked? Do note that high readings will drop as engine warms up and I'm beginning to get some drips from engine, a little oil at stud to the intermediate shaft, some drips on the heat exchanger under oil cooler.

old man neri

Wait, are you saying that your stock sender/gauge was giving you a reading of 275 psi?

whalebird

the above given advice should cover it. It is hard to assume the oprv is the problem if it has been working. i doubt that any of the stock components woul hold up to that kind of pressure.

drv911

I understand what Steve is telling me, to verify that the KD-Tools oil pressure tester that I bought to check the dash gage/sender is giving me a correct reading. The dash gage only reads to 140 psi, by 2000 rpm's the gage is pegged out, the KD tester reads to 300 psi. These high reading are only on cold oil, out side temp of 60 to 70 Fahrenheit. The pressure does drop as engine warms up, the dash gage is showing around 60 psi @ 3000 rpm's @ 180 Fahrenheit showing on the temp gage, in the past I believe this would be about 45 psi. These reading just showed up a few weeks ago, the car's was driven around 40 miles like this. Last summer not noticing any high pressure the car did produce an oil leak on the heat exchanger at the oil cooler. I changed the cooler seals, thermostat O ring and the pressure sender for the oil light and the leak was fixed but I never determined just where the leak had come from.

It just sounds strange to check the tester that was bought to check the dash gage & engine sender.

Brads911sc

Why dont you just try a known good sender? They are $110 new at Pelican... Maybe dC Auto or LA DIsmantlers or a friend has one you can get for less / try out.

drv911

Replacing the sender was the first thing I tried.

drv911

I called KD Tools about testing the tester, they had me call GSI, the maker of the gage. They said I could test there gage by using air pressure. So using an adapter directly from the gage to the air compressor, starting the compressor at 40 psi the GSI gage followed the air compressor gage up to 110 psi, that's the max my compressor will put out. So my high reading are accurate.