Technical Discussion about Oil Pressure

Larry Bastanza

Larry Bastanza

Legendary Member
Tech Expert
Joined
9 February 2000
Messages
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Location
Warwick, NY, USA
Guys,

I spoke to my friend Peter Mills, who tracks a 1997 NSX. He was at Summit Point yesterday and had an oil pressure problem. I beleive this has been discussed before, but I really did not recall a conclusion or definate fix.

Here we go:

At about 7K rpm on the front straight in 4th gear the oil pressure started to drop steadily. As soon as he lifted of the throttle pressure came back up. It was repeatable.

I know this has happened to a few folks. I slept on it last night and I am thinking oil starvation. But I wanted to toss around some ideas and hear a few from you guys about it.

I am thinking if the oil pressure comes up immediately after lifting, then the cause has to do with teh engine reving up in the 7K range. So my first thouth is crankcase pressure, since it will go away as soon as you lift off the throttle. (my theory anyway)

I am wondering (carefully chosen word) if due to crankcase pressure, the oil is not returning properly to the pan from the heads, essentially leaving the pump with no oil.

The other thing is this is a new issue for Peter. He tracks the car regularly, and this is the first time we are talking about this issue. I beleive it has 50K miles.

Peter has steadily increased his skills, but at least a year ago he was driving very fast already, so I am not thinking all of a sudden he has pushed the car past where it was before the symptoms started recently.

I started thinking about deep sump, more oil, things like that, but I am not ready to "add" stuff to this, until I can understand better about the problem.

For those of you going to NSXPO2002, I would really like to discuss this at some point also.

All input appreciated.

Thanks,
LarryB
 
This is an interesting discussion since it seems to be a prevalent problem among people who track their cars hard. I hope to approach this in a methodical manner.

I will be installing a new multi-function Defi digital display that will show oil pressure and temp among other things. It also happens to log readings. I plan to then add the new ARC high capacity/baffled oil pan that we have now and see if this makes a difference. Lastly, I'm looking at using an Accusump. I'm curious if the readings are actual the system running low on oil, or some type of electrical or resonance interference.

Larry ... I'm really curious about Peter's situation since if the pump is indeed encountering starvation, something other than lateral force is preventing the pickup from being able to suck enough oil to maintain pressure. I'm looking forward to Hrant's findings with the new pressure sender.

-- Chris

------------------
Revolutionize your NSX with ScienceofSpeed
www.ScienceofSpeed.com | [email protected] | 877-863-4520
 
OK Guys,

I have some new info.

This situation with Peter's car is not actualy new. He has seen it before but in a very abbreviated manner on the back straight at the Glen.

One pertinent qiestion I have is this a 3.2 related issue or 3.0 and 3.2. Chris, you are running a 3.0 correct?

Thinking a little further I had one other question for Peter which we discussed last evening. Are you blowing any smoke? His answer is no.

So let's say it is starvation, no smoke out the tailpipes, so where is the oil????

I an thinking it is up in the heads and not returning to the sump due to crankcase pressure.

One thought I had was that is the 3.2 engine there was a reducion in the size of the return galleys to fit the larger cylinders, but I am not really beleiving that since I am suspecting this is not isolated to 3.2 engines.

I think the first thing to due is understand if the oil pressure is really dropping as the gauge indicates.

A mechanical gauge placed as discussed in the service manual for testing oil pressure with a long hose so it can be monitored will tell us if the pressure is actually dropping.

I have to say I am having a real hard time thinking the sender is just srewing up, then coming back and working fine, once you lift off the throttle. Just a little too much of a stretch in my mind.

If there is actually a drop in oil pressure I think it can only be starvation. At that RPM you have the VTEC on, so you are even pumping oil at a faster rate upstairs.

Also I have read about folks actually coughing a qt. of oil out of the vent into a bottle in the past. If the vent is attached to the valve cover, and the oil is not going back to the sump, couldn't this be where that quart comes from??

To me it relates to the oil flow rate up to the heads, etc. vs. the flow rate back down into the sump (gravity, maybe fighting crankcase pressure.)

With these things in mind I am sure we can run a few tests on the track at NSXPO to solidify the symptoms at least.

LarryB
 
Well I just went back and read the post of past sighted above by Hrant. It tells me that the mechanical tests have been done already, and it appears as though, from that post, and the data contained, there really is not a starvation issue and oil pressure is actually there all the time.

If that is the case, great, we have some funky senders/gauges and all is well. I still would like to discuss this further and make sure all the data aligns.

LarryB
 
I've always suspected a problem w/ the sendor or gauges because people see the gauge go to 0 regularly but the only oil failures seem to be from either oil pump gear failure or extended high lateral G track use. NSXEE's testing really backs this up, though more data points would certainly be helpful.

It would be nice to finally isolate the specific cause for the gauges to go to 0 on many people's cars.
 
Larry -- It seems as if the oil in the heads is a possibility, but with the pickup being so low in the oil pan, that would mean 3-4 quarts are hanging up there. That's a lot of oil! Yes, I have a 3.0L. I think the best results would be gained with a separate sender and gauge other than factory. Sounds like a good discussion for NSXPO...

-- Chris

------------------
Revolutionize your NSX with ScienceofSpeed
www.ScienceofSpeed.com | [email protected] | 877-863-4520
 
Chris,

I agree. After reviewing the other post it does seem to be a sender/gauge problem, although I think we should discuss it further.

The other thought I had was to understand it more from the electrical perspective in regard to the sender. The sender basically is a variable resistance from ground to the gauge input, best I can tell from the service manual. At first I thought the sender was getting it's ground through the block (as in one wire on the connector from the sender). I will verify on my car at home this evening, but the service manual seems to say a "2 pin" connector for the oil pressure switch.

If the output and ground lead from the sender are on the connector, I would think it is less likely to be a grounding issue, but I cannot rule that out 100% either.

I have seen incredibly small resistance make things like gauges be way off, especially when you put them under the extreme conditions we are talking about.

More Thoughts.......?

LarryB
 
i'am new to the nsx, but doesn't the oil pressure drop occasionally, depending on how hard you push it?
i'm probalby wrong
hey how come my sig aint showin?
 
Originally posted by Larry Bastanza:
Chris,

I agree. After reviewing the other post it does seem to be a sender/gauge problem, although I think we should discuss it further.

<snip>

More Thoughts.......?

LarryB
Click to expand...

Let's rev this topic again, shall we .....
biggrin.gif


Well, 2 days of track testing with a new sender appears to have solved the problem in my case
cool.gif


The gauge did not drop below 2.75 or 3 ..... Only time will tell if this is a permanent fix or the sender will go bad again with heavy use of the full range ....

I have another track event this Sunday and will test it there again. FYI, the ambient tempreature varied from 50F to 65F ......
smile.gif
 
Originally posted by Gokwi:
i'am new to the nsx, but doesn't the oil pressure drop occasionally, depending on how hard you push it?
i'm probalby wrong
hey how come my sig aint showin?
Click to expand...

The oil pressure will fall when the VTEC system is pressurized, however, the "as indicated" pressures shown at WOT near redline on several cars was near zero, even in straight line runs.

I was watching several cars at NSXPO on the track while I was the PSX, and the pressure on the early cars seemed to indicate lower pressures than the later cars in similar situations.

However, it seems that the cause of this looks to be the pressure switch/gauge, and not an accurate indication of oil pressure based on what Hrant and Ed have seen (www.NSXBuilder.com - good write up).

Cheers,
-- Chris

------------------
Revolutionize your NSX with ScienceofSpeed
www.ScienceofSpeed.com | [email protected] | 877-863-4520
 
Well,

We have 2 threads going on about this problem. Anyway, here's a write-up i did some time ago, with some data and findings.

http://www.nsxprime.com/members/dutchblacknsx /OilTroubleFindings.txt

More data has been collected, but is not in here at the moment.


Mich
(Damn Larry....., we really should have met at XPO)
 
I'd like to revisit this topic briefly as I experienced the exact same issue as described by Larry in the intial post. On the track today I almost had a heart attack when I saw the oil pressure dropping like a rock as I passed 7k rpm. I'm getting a secondary sensor for oil temp/oil pressure anyway so that will help confirm that my pressure is not actually that low at high rpm. Was there any resolution to this? :confused:
 
anxious...

Acuraphile said:
See if this answers your question:
http://www.nsxprime.com/FAQ/Troubleshooting/oilpressure.htm

Regards,

Bill
Click to expand...

(Thanks Bill, atleast I can sleep now w/o detonation in mind! :p )

Well, I've been having the same issue as stated by a few on this thread...

Oil-pressure reading of 1.0-2.5 kg/cm, sometimes 0.5 at idle and 4-6 kg/cm at 4-5,000rpms+.

My NSX is a '91 5spd. w/ NA bolt'on mods. I use 5W30 dino'juice w/ OEM NSX filter & 3750mi change intervals. I checked engine oil-level and there was adequate volume. VTEC/cam seals were changed 2.5yrs / 15,000 miles ago. Like all/most NSX owners/drivers, I am fairly aggressive in an enthusiastic way w/ my driving (launching, VTEC, down-shifting, etc'...).

Only other remarkable thing is that I blew one of the two large coolant hoses in the engine-bay about 2months / 1500 miles ago. I immediately stopped the car & pushed it to a safe location. All scheduled maint'/service is upto date. Current outdoor temperatures have been 105-107F, A/C is on high/full-blast as'per Acura's involuntary high-speed fan blower faus paux... :rolleyes:

bold = most prevalent

As far what I've read & come across so far on 'Prime is that only time there's been engine-failures attributed to low oil-pressure, the root causes have been:
- oil-pump failure
- high-speed/high-G oil-starvation (track-related)

Leakdown/compression test recommended or anyother inspection/observation?

Thanks. :cool:
 
WOW, a real blast from the past:). The original problem was solved by replacing the oil pressure gauge sender in Pete's NSX. Never got back to respond:).

Regards,
LarryB
 
With an engine using constant high revs. The vibrations will eventually damage a pressure sensor, especially with it being directly mounted to the engine block.
In my racing experience in many different Race cars all pressure sensors had to be remotely mounted away from the engine with a stainless braided line to avoid this problem.

Maybe this might be a solution to this common problem with Trackday cars?
 
breakin' the seal...

nsxtasy said:
Why? {use of 5W30 engine oil in NSX} :confused:
Click to expand...
Goodson Acura. And what I had lying around in bulk. 10W30 is recommended, indeed as'per manufacturer's recommendations. Had I been residing in a milder/cooler locale, I'd of-course taken more of an initiative to use what is/was recommended.

LarryB, thanks... I'm on it! I'll look up the part & order it, I need the peace-of-mind! :biggrin:

whrdnsx, interesting insight. :cool: If/when I do AEM (for NA 'build), aux' oil-pressure sensor was definitely something I was planning to consider.
 
Well guys I've had the privelege of using two oil pressure gauges coming from the same pressure point. One gauge uses the stock OEM sending unit and the other uses a high quality quick acting electronic sending unit for a Defi gauge setup which I've mounted in a pillar pod along with an ail temp gauge. This is what I've found.

During VTEC operation the oil pressure starts to drop. On the stock unit I find that it drops down to slightly above click number 2 on the gauge. On the Defi gauge which shows readings in lbs., it still is showing over 45 lbs. during full VTEC. It does not drop any lower than that. As soon as I get out of VTEC it jumps back up to 60 to 80 lbs. depending on the engine revs. and load. Normal cruising on the freeway in 5th gear doing around 75-80 mph shows a normal reading of 80 lbs. on the Defi gauge and on the stock OEM gauge it's a little over the 6 mark. My conclusions from this is that we always have oil pressure to the crank and other engine components, and if we lost oil pressure below a certain point, then we also would lose VTEC operation which would be very noticeable. It would act just as if the ECU control unit had turned of the spool valve/hydraulic pressure switch. That doesn't mean we can't starve the engine before this occurs but it would be a very close following.

Since the stock oil pressure unit is so slow and marginal in accuracy, that's why I decided to add a second gauge with better response and accuracy. It's also in lbs. which makes it a little easier to monitor true pressure.

I currently use Mobil 1 10/30w oil and have also installed one of SOS's ARC oil pans.
 
ATERPAK said:
Normal cruising on the freeway in 5th gear doing around 75-80 mph shows a normal reading of 80 lbs. on the Defi gauge and on the stock OEM gauge it's a little over the 6 mark.
Click to expand...

Sounds about right: 6 kg/cm2 = 85.34 psi
 
Aterpak, good info on pressures under various conditions. The spool valve pressure switches are there to act as observation points on VTEC operation. They require a certain pressure to break continuity, and the manual specifies 57 psi as the upper limit. You can jump the VTEC solenoids and use your pressure gauge to check each head to see what the pressures actually are when the switches open. If the oil pressure is ever below these levels the next time VTEC kicks in you'll get a CEL. Since pressures throughout the engine are roughly the same (lowest in the heads), you can get some peace of mind that pressure in the engine will be roughly at the pressure switch break points or higher each time VTEC kicks in.
If you take those measurements, please report back.
 
Spool valve troubleshooting starts on 6-15 in the '91 manual. Pressure switch troubleshooting procedures start on 6-17. Method for reading the oil pressure is on 6-18. The pressure limit for breaking continuity is on 6-19.
 
I believe the reason the oil pressure drops after long periods in VTEC is because the oil pressure sender is located at the very end of the oil path, after the spool valves. If you stay in VTEC long enough, the pressure reading will drop to almost nothing, because the pressure is bleeding off to keep the car on the high cam. I have a mechanical gauge hooked into the same block the electrical sender is in, it will show instantaneous pressure drop when VTEC is engaged. The stock gauge is very heavily damped and takes quite a while to register change.

All this being said, I think the main bearings never see this pressure drop because the oil system maintains enough resistance before the VTEC to keep pressures up in the bottom end.
 

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