[help/opinions needed] Oil pressure won't go past 40psi.

[Jazz86]

Good Evening gurus, 

 

I am having an issue with my L-series L30 motor. I have been chasing this issue for a long time. In short my motor will not be able to go over 40psi of hot oil pressure. I am hoping some of you might be able to shed some insight into this. 

 

Here is a table of the oil pressure when warm. Measurements were gathered using both my mechanical gauge and a custom electrical gauge using a 2% accuracy 150psi pressure transducer. 

 

 

 

RPM                Oil pressure

1000 (idle)      12.5psi

2000               23.9psi

3000               30.2psi

4000               40.4psi

5000               40.6psi

6000               41.8psi

7000               (not attempted)

8000               (not attempted)

 

From 1000 to 4000 rpm the motor has no issue following the rule of (10psi per 1KRPM). Past 4000@40psi the motor will no longer build oil pressure. I suspected many things and began my burning of money to try and fix the issue. Here is a list of things that were done that ultimately did not fix the issue. 

 

1. Upgraded Baffled Oil pan (fixed for oil starvation on track)

2. High flow Oil pump (didn't change anything)

3. Shimmed Oil pump relief valve (no change)

4. Oil filter bypass deleted (lead slug pressed into block)

5. Oil cooler 

 

Any one have experience with this issue? 

 

Thanks, 

J

 

[jonbill]

What modifications does the engine have?

Maybe there's a missing plug in the crank or the front of the oil gallery, or the oil jet to the head is too big or the bearing clearances are much too big.

Edited April 9, 2023 by jonbill

[Jazz86]

8 hours ago, jonbill said:

What modifications does the engine have?

Maybe there's a missing plug in the crank or the front of the oil gallery, or the oil jet to the head is too big or the bearing clearances are much too big.

 

Hi Jon,

 

The engine has quite a bit done to it when I built it my last year of college. 

I don't have the list off the top of my head but here is the short list:

1. Head Ported

2. Isky Cam

3. Triple carbs 

4. Bored over L28 block

 

When I was building the motor it was on the looser side but not out of spec. 

Clearance for the Crank to main bore: 0.0021-0.0025"

Clearance for Rod big end to crank: 0.0015-0.0018"

If the bearing clearances were off wouldn't I see low pressure at idle most? 

 

Crank plugs:

I am not sure but wouldn't that bleed all pressure out of the crank and oil pressure be zero? 

 

Oil Gallery plug:

I am 100% it is in the motor verified when the timing cover was removed for the oil pan install.

 

Oil Jet:

I installed new oil jets when I built the motor

 

Cheers, 

J

[NewZed]

How about a new spring in the pump?

 

Example -

 

https://www.thezstore.com/product/3995/high-pressure-oil-pump-springs-70-83-zzx

 

Here is an old thread about the topic.  I didn't read through it, but the guys in it are typically well-informed.

 

 

[Jazz86]

6 hours ago, NewZed said:

How about a new spring in the pump?

 

Example -

 

https://www.thezstore.com/product/3995/high-pressure-oil-pump-springs-70-83-zzx

 

Here is an old thread about the topic.  I didn't read through it, but the guys in it are typically well-informed.

 

 

Thanks NewZed, 

 

I was really hopping it was the spring inside the oil pump. It does line up with my issue as the oil pressure is locked in at 40psi abouts. 

I have tried two things relating to that oil pressure relief spring. 

 

1. Spring Shim (m4 washer at 0.120" thickness)

 No change in pressure

 

2. DL Potter Oil pump relief springs

No change in pressure even with a single thin washer. 

 

-J

[jonbill]

Didn't you say you'd tried a new high volume pump too?

So can't be that - pressure is being lost somewhere in the system.

I'm really not sure whether the effect of excessive clearances or unplugged galleries will be seen from low rpm or not.

I could be persuaded either way 🤔

Another possibility might be a partially blocked gallery - flows enough to get 40psi at your measuring point, but no more.

I suspect the true diagnosis can only come with stripping the engine  down and checking everything.

[NewZed]

On 4/8/2023 at 10:29 PM, Jazz86 said:

40psi of hot oil pressure

What is cold pressure?

 

What oil?

 

Not clear what this, below, would accomplish.  It forces the oil to always pass through the filter.  The filter bypass is meant to guarantee oil supply to the galle(r)y, even if the filter blocks flow.  Pressure comes from forcing the oil through all of the various bearing gaps after the filter.  Are you sure that this was done after the problem and not before?

 

On 4/8/2023 at 10:29 PM, Jazz86 said:

4. Oil filter bypass deleted (lead slug pressed into block)

 

[Jazz86]

11 hours ago, NewZed said:

What is cold pressure?

 

What oil?

 

Not clear what this, below, would accomplish.  It forces the oil to always pass through the filter.  The filter bypass is meant to guarantee oil supply to the galle(r)y, even if the filter blocks flow.  Pressure comes from forcing the oil through all of the various bearing gaps after the filter.  Are you sure that this was done after the problem and not before?

 

 

Glad you asked!

 

Oil is 5w40 rotella T5.

On a 75F day a cold start with idle RPM at 800rpm the oil pressure is at 25psi. Give it a small rev to 2500 rpm the oil pressure again tops out at the same pressure around 40psi maybe a little higher at 42psi. I have not logged that using my transducer setup. The pressure shoots up and hits a wall at 40psi.

 

As for the bypass plug. Was worried that it might be the cause of my issue as this was the only original part of the motor. Weak spring pressure, maybe causing the lack of pressure as it always tops out at 40psi. But I was clutching at straws.

 

[Jazz86]

23 hours ago, jonbill said:

Didn't you say you'd tried a new high volume pump too?

So can't be that - pressure is being lost somewhere in the system.

I'm really not sure whether the effect of excessive clearances or unplugged galleries will be seen from low rpm or not.

I could be persuaded either way 🤔

Another possibility might be a partially blocked gallery - flows enough to get 40psi at your measuring point, but no more.

I suspect the true diagnosis can only come with stripping the engine  down and checking everything.

 

Yep I tried a few combinations of oil pumps and springs. 

 

OEM Style Oil pump OEM spring: 40psi max pressure

OEM Style Oil pump with OEM spring shimmed with 0.120" M4 washer: pressure still topped out at 40psi I did notice a quicker response to the oil pressure on my mechanical gauge. This could be a false since this is all "eyeball" on how fast the mechanical needle rose. 

 

280ZX AT Turbo High Volume pump with factory spring: 40psi max pressure

280ZX AT Turbo High Volume pump with 0.120" washer: 40psi max, again quicker response to oil pressure. 

280ZX AT Turbo High Volume pump with LD Potter springs: 40psi max, again quicker response to oil pressure. 

 

At this point I was really sad about it all so I kept the 280ZX pump on and moved on to trying different things. 

[Jazz86]

Quick update on the issue. I changed my oil and on the first crank I saw the needle on the mechanical gauge shoot to 65psi on the first rev to 3000rpm. This had me excited and the oil pressure would keep pegging out to 65psi with each small rev. Then I shut the car off to go clean up a few things, returned to the car and on the second start the oil pressure is back to topping out at 40psi. 

 

Checked oil level and it is right at the top of the dipstick. 

 

Drama summarized here:

1. Oil change with fresh oil 5w40 rotella, first start after new filter and oil

     -Oil pressure while cold and at 3000rpm is at 65psi 

 

2. Shut engine off

 

3. Start engine again 

    -Oil pressure is back to 40psi Max (cold oil rpm at 2500, oil pressure is back to being pegged at 40psi)

    -Hot oil pressure is 4000rpm is again at 40psi max.

 

Possible causes?

Clogged pickup?

Jammed oil pressure relief? 

 

At a loss here, Again thanks for all the suggestions!

 

-J

[NewZed]

jonbill's suggestion of a blockage in a passage seems reasonable.  It would have to be before the gauge port.  And moveable.  Something that opens after sitting then gets pushed to block flow.

 

A gauge on the oil filter might tell something.  Here's an example, not sure what measurements you would need.

 

https://www.amazon.com/GlowShift-Filter-Sandwich-Adapter-Thread/dp/B007SXGAZQ

 

 

 

 

 

 

 

[Jazz86]

Thanks guys!

On 4/9/2023 at 11:40 PM, jonbill said:

Didn't you say you'd tried a new high volume pump too?

So can't be that - pressure is being lost somewhere in the system.

I'm really not sure whether the effect of excessive clearances or unplugged galleries will be seen from low rpm or not.

I could be persuaded either way 🤔

Another possibility might be a partially blocked gallery - flows enough to get 40psi at your measuring point, but no more.

I suspect the true diagnosis can only come with stripping the engine  down and checking everything.

I got to tearing apart my oil cooler set up and the oil pressure line on the gauge. I used compressed air, thin metal wire and a spray bottle filled with thin oil to see if there was any obstruction between the post oil filter union and the block. 

Please excuse the horrible diagram as it was drawn on my phone during my lunch break. 

 

There doesn't seem to be any thing blocking between the post filter union and the oil sensor location. For reference I am using the OEM location where the OEM electronic sending unit would be instead its plumed to my mechanical gauge. 

 

I will make plans to measure the pressure drop before and after the filter and at my gauge location as I can do that with two pressure transducers. I will report back to this page if there are any interesting results. 

 

3 hours ago, NewZed said:

jonbill's suggestion of a blockage in a passage seems reasonable.  It would have to be before the gauge port.  And moveable.  Something that opens after sitting then gets pushed to block flow.

 

A gauge on the oil filter might tell something.  Here's an example, not sure what measurements you would need.

 

https://www.amazon.com/GlowShift-Filter-Sandwich-Adapter-Thread/dp/B007SXGAZQ

 

 

 

 

 

 

 

 

[NewZed]

15 hours ago, Jazz86 said:

oil cooler set up

 

You don't show the oil cooler in your drawing.  

 

A follow-up on why a gauge on the filter housing might tell something.  After it leaves the filter it hits the small main oil galle(r)y passage.  Then it splits up and down.  You will have maximum possible pump pressure in the oil filter.  If you get the same number in the filter as at the port then you'll know that something before the filter is the problem.  If after, then you can stop looking at the pump.

 

Don't forget also the Bernoulli and Venturi principles.  If you have some sort of obstruction in front of the oil pressure port the moving oil can actually cause a pressure drop at the port opening.  Which makes me think that maybe your fixture at the gauge port is projecting in to the oil galle(r)y channel.  

 

https://jacobsanalytics.com/eductors/venturi-eductors/#:~:text=Basically the Venturi vacuum pump,partial vacuum in the process.

 

[jonbill]

Fwiw, the front jet in the head actually supplies oil from the head to the timing chain tensioner gear.

[Chickenman]

I've seen Oil Pump Screens partially blocked Silicone Sealant. Especially by so called " Mecahnics " who goop the Oil Pan with the stuff. Draining Oil will sometimes allow silicone to drop off screen. Thne float around till it partially clogs screen again.

 Oil screen pickup too close to bottom of pan can also cause an Vortex effect that affects oil pressure. Screen should be no closer than 1/2 inch from bottom  of pan .  

 You also say you have a Turbo Oil Pump. But is it an OEM Nissan Aluminium Pump. I seen some of the Cast Iron aftermarket pumps lacking in pressure output because Internal ports or claerance are machined wrong. Surprisingly some of the Melling pumps are causing issues at higher RPM's. I've had a couple of customers have issues with Melling Crat Iron Pumps. Strange, because thye are normally good quality. 

 You can still purchase OEM Nissan Aluminium Turbo Oil Pumps from Nissan. 15010-S8000. And Rock Auto sells Hitachi made OEM Nissan Turbo Pumps. Hitcahi is an OEM Maufcaturer for Nissan. 

[Jazz86]

!!!!!!!!!!!SOLVED!!!!!!!!!!!

Special thanks to @jonbill @NewZed for helping me with suggestions. I thought I would post my findings here so in case anyone in the future has my issues you might find some insight into your issues. Happy racing!

 

To recap things we looked at:

1. Upgraded Baffled Oil pan (fixed for oil starvation on track)

2. High flow Oil pump (didn't change anything)

3. Shimmed Oil pump relief valve (no change)

4. Oil filter bypass deleted (lead slug pressed into block)

5. Oil cooler 

 

You all suggested 

6. Oil pump springs (confirmed not the issue with several spring configurations and preloads)

7. Oil pump tried 240z Standard pump (springs tested no change)

8. 280ZX AT high volume pump (springs tested no change)

9. Cleaning oil channels from the oil filter to various locations on the block (nothing clean as a whistle)

10. Pressure drop from the oil cooler and or oil channels

 

@NewZed I sat on what you showed me with Bernoulli and Venturi principles. Out comes my old college text books! I will leave all my mock math out of this post for simplicity. I found a large restriction at my oil cooler system, at the heat exchanger. I removed the oil cooler system completely and the engine now had a peak pressure of 75psi. A few small revs and my mechanical oil pressure gauge would flick really quickly and I verified the data on my electronic oil pressure transducer setup. Meaning the oil cooler setup was causing a significant pressure drop. Those who have read the whole story will say, "but wait Jazz, you said you always had low oil pressure". I did, and what I also suspected was the oil relieve valves. Sadly I was an idiot and did both the oil cooler and pressure relieve valve around the same time and never really drove the car above 3000 rpm. So my bad, and onwards to the story. 

 

Here is a bad drawing of my oil cooler setup.  

 

 

So to simplify the pressure drops of the whole system with warm oil I will talk of peak oil pressure that is generated and the final pressure at my gauge with all the restrictions on it. 

 

Without Oil cooler setup, just filter on block, peak pressure was 75psi. 

 

With Oil filter adapter, 3 90 degree fittings, 10AN lines and a Mishimoto oil thermostat and a bypass line peak pressure was now at 70psi.

 

With oil filter adapter, 3 90 degree fittings, 10AN lines going directly to the Mishimoto oil cooler (heat exchanger) peak pressure was at 45psi. 

 

With Oil filter adapter, 3 90 degree fittings, 10AN lines and a Mishimoto thermostat and the mishimoto heat exchanger (oil cooler) peak pressure is at 40psi. And noted sluggish oil pressure readings. All the above configurations yielded a very fast response from the oil pressure gauge. Funny enough the oil pressure gauge is so quick to respond it can almost double as a tachometer.  

 

So I have now confirmed that the oil cooler heat exchanger from mishimoto is trash and that my oil bypass was also the cause of the issue. Looking into more into the data looks like Mishimoto does not release official data on their heat exchangers. This is a red flag for me and I am stupid for not trusting a cooler without any form of datasheet. Shame one me I should have my engineering degree taken away. 

 

A quick skim on the interwebs about mishimoto oil coolers showed thier engineering report on a test they ran on a car. I will include that document below in case Mishimoto reads this post and takes down their findings. mmoc-gen4-10_engineeringreport.pdf . Here is a snip of their readings before cooler and after cooler:

This looks like a 10psi oil pressure drop from the 19 row cooler. That is A LOT considering the motor was not being revved out. More red flags on mishimoto's oil cooler heat exchangers.

 

I was looking into other oil cooler heat exchangers to see if other makers were expecting similar pressure drops. Sadly there isn't much data on it but lucky I remembered my track 350z is running a 19row Setrab cooler setup and I have not had any issues at all on the street and on track. Oil pressure was the same with out without the Setrab oil cooler setup. 

 

Luckily I found Setrab's data on their coolers. See screen shot below: 

Setrab has estimated numbers for their coolers, and how much heat they can dissipate along with the change in pressure from running one of their coolers. Visit their site and you can see the engine parameters of where they got their numbers and what speed and oil pump flow etc. Here is the link: http://www.setrabusa.com/products/oilcoolers/engine/index.html

 

So I thought, why the hell not this car is already a money pit. I bought a the same cooler that I run on my 350z track car. This motor should be pushing 300hp crank like my 350z does. I installed the new Setrab oil cooler to my existing setup and low and behold pressures are all good. Peak pressure is now at 65psi. This should be fine for my motor. I will be sending black stone labs an oil sample to see if there was any damage to the bearings but so far so good. 

 

Again thank you all for those who had input. I will see you all at the track!

 

CAUSE OF MY LOW OIL PRESSURE:

OLD OIL PRESSURE RELIEVE VALVE 

POS MISHIMOTO OIL COOLER (HEAT EXCHANGER)

 

 

 

 

 

 

 

 

[Jazz86]

On 5/13/2023 at 3:29 PM, Chickenman said:

I've seen Oil Pump Screens partially blocked Silicone Sealant. Especially by so called " Mecahnics " who goop the Oil Pan with the stuff. Draining Oil will sometimes allow silicone to drop off screen. Thne float around till it partially clogs screen again.

 Oil screen pickup too close to bottom of pan can also cause an Vortex effect that affects oil pressure. Screen should be no closer than 1/2 inch from bottom  of pan .  

 You also say you have a Turbo Oil Pump. But is it an OEM Nissan Aluminium Pump. I seen some of the Cast Iron aftermarket pumps lacking in pressure output because Internal ports or claerance are machined wrong. Surprisingly some of the Melling pumps are causing issues at higher RPM's. I've had a couple of customers have issues with Melling Crat Iron Pumps. Strange, because thye are normally good quality. 

 You can still purchase OEM Nissan Aluminium Turbo Oil Pumps from Nissan. 15010-S8000. And Rock Auto sells Hitachi made OEM Nissan Turbo Pumps. Hitcahi is an OEM Maufcaturer for Nissan. 

 

Yes, I have a genuine Nissan Turbo oil pump. I also compared the height of the rotor to several pumps and confirmed that it is indeed the high volume pump. 

 

Oil pickup being clogged was a small possibility. When I first took the OEM pan off to go to my new baffled pump I looked at the pickup and it was clean. I did a pretty clean job of installing the baffled pan, but hopefully there isn't anything there like when I first built the motor. 

 

 

[NewZed]

Congratulations on finding the source.  I'm not really clear on what your picture is showing or how the cooler is supposed to work.  But, regardless, if you keep working back to the basic principles on a problem eventually you have to find the solution, as you did.  Good luck.