Should the oil pressure reading move at constant RPM?

[burbel]

Hey all, looking for a bit of advice before I try and tear down and replace the motor on my NSX. I noticed once that the oil pressure reading dropped very close to zero at high rpms, since then I have been trying to track down the culprit.

I just replaced the oil sender unit attached to the engine, as well as the guage cluster that shows both coolant temps and oil pressure. During the test drive I noticed that the oil pressure reading was more sensitive than before, and moved faster and more often.

However, on the leg back from the test drive, after the oil had reached a steady temperature (I would assume), I noticed that, while driving on the highway at contant RPM, the pressure reading kept changing.

I was running in 5th gear at around 3200 rpms (type-R R&P), and the pressure would oscillate (not smoothly, but often) from around 3.5 to 4.5. After I turned off the A/C, less that complicate things, the same behavior remained.

My only thoughts now are that either a) the oil pump is dying (possibly the gears are wrecked? I saw that in another post) or that there is some obstruction in the flow of oil around the engine...

Any ideas?

 

[DutchBlackNsx]

Enough reading here


Mich

 

[burbel]

Thanks for the link, Dutch - the original problem that once the oil pressure near redline was low caused this whole thing to start, I pored over the post you referenced (Still have a printout in the tool chest). However, that post was mainly about at redline, what I am trying to see is the behavior at a far more reasonable RPM - around 3,500.

From that list I came to the expectation that the pressure should match the rpms, close to 1 at idle, close to 8 at redline, and scale in between. But the point of my caution is that, at constant RPM, the reading fluctuates. Has anyone else seen this?

 

[Larry Bastanza]

I think the first thing that needs to be done is get a mechanical oil pressure gauge hooked up. This is a really important step as Ed points out in the other thread. Regardless of what RPM the gauge changes and/or fluctuates, you need to make sure that the oil pressure IS really changing.

You may be pleasantly surprised.

HTH,
LarryB

 

[burbel]

I was talking with some friends about doing exactly that, however, they both have oil gauges with small cables - do you know an a mechanical oil pressure gauge that would a) fit the NSX, and b) I could easily route into the cockpit to watch pressure while driving around?

Or is there some other way to get the oil warmed up? I was always warned not to rev a car while it was sitting idle.

 

[MarkB]

...is there some other way to get the oil warmed up?...

Oil takes quite a while to cool off.

What I would do is install the guage, start the car and let it idle for say 5 minutes, and then you can safely rev the engine from the throttle body.

 

[DutchBlackNsx]

Burbel,

Next to the pressure drop-of at high RPM, i also have the same problem as you describe, where the pressure seems to have it's own live at the same RPM. Never lower then 4, but sometimes up to 7 bar, at the same RPM.
I believe the relief-valve start opening at approx. 3500 RPM, so the pressure should be steady at that point (discard VTEC drop), but mine seems to go up after that sometimes as well.......
I also have replaced relief-valve-spring, and pressure sensor.
After replacing the sensor it went all it bit better, but not spectaculair............

There was a post from someone having the same problem, but i can't remember where or who.....

What i suspect of that particulair problem, is the little connector from the pressure sensor into the wiring harness. If this little guy has the smallest bit of resistance, it will have a large effect on your in-dash gauge.

I sorta given up on the oil-pressure mystery, until someone sorts it out, in the mean time, i just hit the revlimitter as often as i can ......



Mich

 

[Larry Bastanza]

On the same line of thinking as Mich, last year at NSXPO Ed (nsxbiulder) and I, and a few others, had a discussion as we were looking at an NSX engine on the stand. This oil pressure sender only has one wire. The "return" or ground for this sensor is the block. We were quite suspicious of this and thought about either soldering a wire to the sender case and hard grounding it, Ed came up with the idea of making a spring-clip and secure it against the body of the sensor.

I do not think Ed had a chance to do it, and I unfortunately did not. I do know that once Ed used a mechanical gauge it did become less of an issue, since it was determined to be a gauge/sender problem rather then a true oil pressure issue.

HTH,
LarryB