Oil pressure

[John Vardanian]

Out on the freeway today I started out with the normal 80 psig oil pressure but somewhere along the way it dropped to about 40. There are no leaks and the engine doesn't sound any different. What could’ve happened?

What happens when the oil pressure valve doesn't function properly? Could this be the culprit?

Thanks.

john

[whturner]

Hi John:

Was the engine completely warmed up when you had #80? Seems a bit high.
Were you still at the same speed when it dropped to #40?
Is it #80 again the next time you drove on the freeway at the same speed?
Finally, what are the Factory specs for oil pressure at various RPMs?

Cheers
Warren

[Rudy van Daalen Wetters]

John,

The first thing I'd check is if the gauge is registering correctly. Maybe you could hook up a manual test gauge to experiment with. Also, you should tell us at what RPMs you were taking these readings and the oil temperature at the time. My Maserati Mexico starts at 120 lbs when cold and drops to half that when fully warm. Nature of the beast on that motor and quite common.

Rudy van Daalen Wetters
1963 GTE s/n 4001
1966 330 S/n 8705

[John Vardanian]

Warren,

Answer to your Q's:

Was the engine completely warmed up when you had #80? Seems a bit high.
Yes. 75-80 is my normal read at full operating temp.

Were you still at the same speed when it dropped to #40?
Yes.

Is it #80 again the next time you drove on the freeway at the same speed?
No. It is still about 40 psi at hi RPM and about zero at idle.

Finally, what are the Factory specs for oil pressure at various RPMs?
I do not know, but my outside plug 250 has this same kind of pressure: 30-40 at idle and 75-85 at high RPM.

I will check the gauge (Rudy), but somehow I do not think it is the gauge.

john

[whturner]

Hi John:

Your first guess is a likely reason - but there are, I am sad to say, worse possibilities.
I did have that happen to me once (on a 46 Ford - but hydraulics are hydraulics). The oil pressure plunger spring broke, so full oil flow through the controlling valve could now take place. Gave the same symptoms - lower pressure throughout the system.
But check the gauge function first, as suggested. And then try to raise the pressure by adjusting the pressure control valve. Should be informative, whether it works or not.

Cheers and good luck
Warren

[John Vardanian]

I wanted to close the loop on this issue.

I removed the oil pan to inspect the short section of rubber hose in the scavenger plumbing, suspecting it to be the culprit. But the hose was fine. The strainer (what works as a filter in these old engines) wasn't clogged either. I lastly removed and cleaned the pressure relief valve. Now everything is back together and the pressure readings are normal.

The only problem was that the preset pressure got lost since the valve had to be dismantled. I understood that the setting should be 40 psi at idle and 85 at higher RPM's, with the cutout right at about 85. It was a given that attempting to dial in the pressure with the car's own gauge would be a futile exercise. So, I cut in a real gauge to set the thresholds. I don't think it is quite zeroed in yet. It will take some trials on a road trip.

john

[sjvalin]

Excellent, John! Will you be driving the old girl to Monterey this year?

-steve

I wanted to close the loop on this issue.

I removed the oil pan to inspect the short section of rubber hose in the scavenger plumbing, suspecting it to be the culprit. But the hose was fine. The strainer (what works as a filter in these old engines) wasn't clogged either. I lastly removed and cleaned the pressure relief valve. Now everything is back together and the pressure readings are normal.

The only problem was that the preset pressure got lost since the valve had to be dismantled. I understood that the setting should be 40 psi at idle and 85 at higher RPM's, with the cutout right at about 85. It was a given that attempting to dial in the pressure with the car's own gauge would be a futile exercise. So, I cut in a real gauge to set the thresholds. I don't think it is quite zeroed in yet. It will take some trials on a road trip.

john

[Michael Bayer]

John I would first examine the pressure regulator to check its ports and freedom of motion first, as if it should fail, the engine could be harmed, then after, move to examine the guage. I believe these gauges were calibrated such that when the engine was fully warmed and with proper weight oil, they displayed near dead center of scale, with higher readings cold. M

[John Vardanian]

[quote="sjvalin"]Excellent, John! Will you be driving the old girl to Monterey this year?

-steve

Yes Steve. We are. We plan to stop by the gathering Thursday evening.

JOHN