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Sat May 10, 2025 10:10 am

Hi experts.
I have a sky-high oil pressure problem. Up to about 3000 rpm, the pressure is normal, 45 pounds. Above that rpm, the pressure climbs to peg the gauge at 80 pounds.
I've removed the two oil pistons and blown compressed air through the gallery. No change.
I've removed the piston at the flywheel and run it.
No change.
I've stuck a wire up the flywheel gallery supply line, but it couldn't make the turn.

I believe there's a plug in the oil gallery somewhere, and I'm hesitant to take the world apart to gain access to all the gallerys.

Any Ideas?

Sat May 10, 2025 10:46 am

What kind of oil pressure guage & sending unit. I think VDO has 2 different sending units with a different range(0-80 & 0-150psi) and must go with the matching guage. I would test actual pressure with a mechanical guage at the sending unit port.

Sat May 10, 2025 10:52 am

DerrickfromNC1 wrote: What kind of oil pressure guage & sending unit. I think VDO has 2 different sending units with a different range(0-80 & 0-150psi) and must go with the matching gauge. I would test actual pressure with a mechanical gauge at the sending unit port.

what Derrick said ^^^

Also, you need 10 PSI per 1000 RPM. I manage my oil pressure to about 12 - 14 psi per 1000 when the oil is at max temp, by choosing a viscosity that allows that.

Sat May 10, 2025 11:34 am

The oil pressure was fine at all rpm's, until I took the engine out to find a vacuum leak at the intake manifold boot.

Then the problem. I bought the 80 psi gauge and sender at the same time

Sat May 10, 2025 12:45 pm

Eric Hodges wrote: The oil pressure was fine at all rpm's, until I took the engine out to find a vacuum leak at the intake manifold boot.

Then the problem. I bought the 80 psi gauge and sender at the same time

Have you cross checked the sender number to the gauge to be sure they sent you the correct one? Have you tried the old gauge from when the engine worked fine? I guess you had a gauge before to be able to make the statement that it worked fine before. Does the new gauge have settings that are configurable if it is not an older style VDO gauge?

Sat May 10, 2025 5:56 pm

The gauge and the sender are old.

Sat May 10, 2025 6:06 pm

Eric Hodges wrote: The gauge and the sender are old.
what is the gauge model number and the sender number?

Sat May 10, 2025 6:09 pm

Eric Hodges wrote: Hi experts.

I've removed the piston at the flywheel and run it.
No change.
I

Hold on, do you mean you removed the plunger and spring and put the threaded plug back and ran the engine

OR
you left the threaded plug out and ran the engine with the thing just open?
huh, well, no, that would let all the oil drain out right?

Need clarity on this. :shock:

The oil relief bore should have two holes drilled sideways through it in the bore.
one near the top which is where the oil passes back into the sump when the plunger gets pushed down, and the other below the plunger which is a vent.
Both those holes need to be there for it to work.

Sat May 10, 2025 6:16 pm

Tho it's not a great angle, in this cutaway pic you can see the two holes drilled horizontally through the flywheel side oil plunger bore.
the upper hole exits into the case between the lifter and the pushrod tube.
the lower hole goes into the inside of the sump about at the oil level

Sun May 11, 2025 5:11 am

Just to clarify.

The oil pump/sender was purchased in 2016-ish and not changed, not removed not replaced.

The oil pressure regulates properly from about 1500 to 3000. It rises to 45 psi and stays to about 3000 rpm. Then, as the rpm rises, the oil pressure rises to 80 psi, pegging the gauge.

I removed the piston and spring from the forward (flywheel) plunger and replaced the threaded plug. No leaks.

Sun May 11, 2025 5:19 am

My guess is a plugged gallery somewhere, and I don't relish the thought of tearing it apart and sending the cases out for a hot tank....

Sun May 11, 2025 6:59 am

Eric Hodges wrote: Just to clarify.

I removed the piston and spring from the forward (flywheel) plunger and replaced the threaded plug. No leaks.

Do you mean, that you removed the piston and spring completely, and put the plug back with no piston/ spring?
If not, what exactly did you do?

It sounds like, the issue is with that spring and piston, as it should open to dump the high pressure you are seeing. I would look for another OEM spring and piston, and make sure the piston edges are eased, and check that it moves freely in the bore.

Sun May 11, 2025 9:48 am

What size of oil pump? 30mm?

Sun May 11, 2025 6:16 pm

I found the problem.
My apologies for sending you all out on my wild goose chase,

Sudden problems tend to point to the last thing you did, which in my case was R and R the engine. Everything was disconnected and reconnected. The thumb nut on the sender, that goes to the gauge, was loose.

I tightened it and I now have 40 psi no matter what the rpm.

Fixed.

Sun May 11, 2025 9:55 pm

Eric Hodges wrote: I found the problem.
My apologies for sending you all out on my wild goose chase,

Sudden problems tend to point to the last thing you did, which in my case was R and R the engine. Everything was disconnected and reconnected. The thumb nut on the sender, that goes to the gauge, was loose.

I tightened it and I now have 40 psi no matter what the rpm.

Fixed.

So....at 850 rpm idle you have 40 psi....and like....at 4500 rpm you have 40 psi?

Not quite so sure that is an improvement.

Ray