Oil Pressure Question

[John Straub]

I've just finished doing a rebuild on my '67. The car had been sitting since '74. The oil pressure goes up to 20 on the gauge and the engine runs great. When I did my '65 many years ago I remember reading about a oil pressure valve up-grade with a different piston and spring that gave the engine a higher oil pressure reading.

Have any of you ever heard of such a thing? I just don't remember, but it seemed to work.

Any ideas?

Thanks John

[Flieger]

Generally accepted proper oil pressure is 10 psi - 14.7 psi(1Bar) per 1000 rpm.

When the "oil bypass mod" is done, one must use an updated pressure limiting piston and spring. If the old style is used, it will cause very low oil pressure.

The "oil bypass mod" involves drilling a hole in the oil return tube (cast as part of the case) which diverts excess oil pressure back into the pressure side of the oil pump, rather than into the case. This keeps the sump drier for less frothing, and allows a smaller scavenge pump, making way for a bigger pressure pump.

[JKH]

early oil pressure relief caps were round and slotted, a tech bullitin was to add a 3mm (?) shim, Then it was replaced with a slotted round with a groove cut in the round diameter(denoting the upgraded version)
The latest version has a hex head .
http://www.pelicanparts.com/catalog/...g11.htm#item44

[edmayo]

John, if that's all the pressure you get when revving the engine you don't have nearly enough. Just to eliminate all electrical gauge/sender issues, I'd suggest temporarily installing a mechanical gauge, nothing fancy, just in the engine bay. Then compare those readings to what your electrical gauge showed. When revving the engine with cold oil you should be seeing more like 80-90 psi.

[VintageExcellen]

John, if everything seems ok except the reading you get at your gauge then swap the sender with one from one of your other cars.

I had a 70 911T with bad oil pressure once, changed the pressure sender and everything was ok.

If an oil bypass mod was ever done then the right oil pressure relief spring and piston must be used.

General rule of thumb is 10psi per 1000rpm. Pressure will be higher when the engine is cold.

[John Straub]

Thanks guys...I'll start checking.

John

I ordered a new sender.

[66S]

Adding shims [washers] under the relief valve spring usually increases oil pressure. Was the crank re-plugged? Ive heard of them coming out. First use a mechanical gauge to check pressure.

[John Straub]

OK... I got a new sender and put it in.

Before the oil pressure would not go above 20. Now I get a pressure of about 40 at idle, it goes to 60-80 at 2000rpm, and goes to 140 at 3000rpm and above. Does the gauge need to be calibrated to a new sender? When I put an external gauge on it I get the same readings. Any ideas? Is it bad to drive it like this?

John

[Flieger]

The pressure relief springs should kick in by about 100psi. You either got a later sending unit, which I have heard will cause weird gauge readings, or you are giving the cold oil pressure readings.

[John Z Goriup]

OK... I got a new sender and put it in.

Before the oil pressure would not go above 20. Now I get a pressure of about 40 at idle, it goes to 60-80 at 2000rpm, and goes to 140 at 3000rpm and above. Does the gauge need to be calibrated to a new sender? When I put an external gauge on it I get the same readings. Any ideas? Is it bad to drive it like this?
John

If the in-car, dash-mounted gauge reading is the same as the external mechanical direct-reading gauge you don't really have a problem in that area.

a couple of questions first, John:
1. Are you using the stock oil pump.
2. Is the idle oil pressure reading a cold reading or a normal operating temp reading ?

re "Is it bad to drive like this ?" In my opinion , yes, for the simple reason that the gauge only reads to 140 psi and you cannot be absolutely certain how much higher your actual oil pressure is at higher rpm. 140psi is certainly higher than normal and just not necessary for extended engine life. The real & biggest danger with that kind of oil pressure is blowing out the engine oil cooler. They are expensive.

North Hollywood is restoring, rebuilding my original oil gauge as we speak , because I had the exact same indications you are experiencing. They did not feel that calibrating a gauge to a new sender was necessary, and since your on-board gauge and the external reading match.....you're OK.
A good part of the reason I had problems is the inclusion of a GT3 oil pump with vastly higher oil flow without any other changes.

After much thought & consultation, my suggestion is to cut one coil off the relief spring and check oil pressure at 3000 rpm or higher with external mech. gauge. If it's still over 110psi trim off another coil and you should wind up with approx. 90-100 psi at 3-4000 rpm. I submit that's a good, safe reliable oil-pressure that'll provide all the lubrication needs of the engine while preserving pressure sensitive components.

Good Luck

JZG