Oil pressure and the answer

Coming back from a canyon drive, I noticed an odd flicker on my oil pressure gauge.

The first time it was just in my peripheral vision and I wasn't quite sure what I saw. The second time, I was in first, pulling away from a stop sign. My oil pressure climbed with RPM, passing the 60lb/in2; mark, and got most of the way to 90lb/in2; for just a fraction of a second before dropping back down to its regularly scheduled ~60lb/in2; steady state.

Before and since, oil pressure has been great and predictable. The motor is a 2001 with VVT, it has <20k miles on it and was treated extremely well before I got it. Oil pressure climbs with RPM to somewhere around 60lb/in&sup2; and stays there.

What the heck is going on? I'm concerned about the pressure actually falling while the RPMs are climbing. If this is the relief valve kicking in, why did the pressure get past the target pressure? And why doesn't it do this all the time?

Factory oil pressure gauge?

Yes. The real one.

Based on the history of the motor, I'd guess a bad sending unit. The idiot light in most cars will go off both if the pressure(according to the sending unit) goes too high or too low. Throw a quality sender at it and go from there.

I'm using the sending unit from the original '94 motor. It's not an idiot gauge.

In reply to peter:

Ah, brainfart, I figured it's not an idiot gauge but whenever I hear flicker I think warning light going off. Still probably a bad sender, especially one with 20 years on it.

Not a problem, I should have mentioned this is a later motor in an earlier chassis.

I'm not buying the failed sender idea, it's worked fine other than this incident, and the trip above 60 was very short, and also the gauge has been very consistent otherwise.

Puzzling. Appreciate the input!

Oil not at full operating temperature, maybe?

In reply to BoxheadTim:

Should have been plenty hot coming back from a canyon drive. Given the history of the engine, I'd doubt the relief valve is sticky. Which pretty much only leaves an electrical fault as a reasonable explanation.

Oil pressure at idle can drop very low, especially when the oil temp is high.

I have seen cars with automatics that it makes a difference whether in drive or neutral. Idle speed being the key.

So yes, most likely it is the sender/gauge, or your idle speed had dropped.

If your pressure is good while driving, don't worry about it.

A famous race mechanic was noted as saying 10 psi per 1000 rpm oil pressure is sufficient.

Oil was very much up to temp, as Kenny points out. Idle pressure is good, this 'drop' happened about 3/4 of the way through 1st.

If the car did this consistently, I'd be more inclined to call it normal, the fact that it's intermittent concerns me. But electrical faults are often intermittent... I'll check the connection and consider replacing the sensor...

The most likely suspect is a bad wiring connection between the sender and the meter, that disconnected for a moment and then went back to normal.

At least, that's what I would diagnose if your sender works like the usual kind I'm familiar with -- I was taught the sender's resistance increases as the oil pressure increases; at lower pressures, the sender allows the meter voltage to shunt to ground. If the connection between the sender and the meter is broken, the gauge swings all the way over to max.

So if you have intermittent jumps of the gauge to the high side, the suspect is intermittent breaks in the circuit to the meter. If you have intermittent jumps to the low side, the suspect is a short in the circuit that's putting the meter voltage to ground.