Low Oil Pressure on Fresh Build

Nissan 300ZX technical discussion forum: Maintenance, performance, installations, modifications, how-to's and troubleshooting.
WhiskeyyMike
Posts: 11
Joined: Mon Mar 01, 2021 12:13 pm
Car: 1993 Nissan 300ZX TT

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Hey Guys!

Recently had a built long block installed into my '93 and am having a bit of an issue with the oil pressure.

Very low miles on the new engine. Just dyno break-in plus probably less than 50 miles on the road. The car only has a base tune right now as the shop wasn't happy pushing the power up with the oil pressure staying pretty low as it is.

The car idles at around 12-13psi. But at around 3000rpm(no load) it's only getting up to around 32-36psi. Standard pressure from what I could see in the service manual should be in the 50s at that RPM.

Both those pressure numbers are no load with mechanical pressure tester. The sending unit was toast so I won't have a real reading under load until I get the replacement in later this week.

The car sounds and feels completely fine and healthy. Changed the oil and filter to check for any signs of extra wear or any shavings and it looks fairly normal.

The shop didn't build the engine, but they believe the bearing clearances are too loose. I just wanted to see if anyone had any other ideas. Just wanted to knock out all the possibilities I can check before we decide to pull the engine again.


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VStar650CL
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If you already changed the filter, there isn't much external that could cause that. Might not be the mains, but it's almost certainly something internal.

WhiskeyyMike
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Joined: Mon Mar 01, 2021 12:13 pm
Car: 1993 Nissan 300ZX TT

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If it wasn't the mains, what could it be? I know I've seen some talk about oil pickup tubes failing to build pressure if they were damaged if the pan takes a hit, which my oil pan is certainly mangled and dented from the previous owner.

While I would've thought that was something I or a shop would notice when installing the tube/pan, it very well could've been overlooked. If the actual tube was bent or crimped, I think I would've seen it (THINK, but I def could've missed it). But if the head of the tube was damaged, I could very well have not even noticed anything was wrong.

itsa300zx
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Car: 1990 300zx NA W/TT swap
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FYI the pickup tube mouth to the oil pan is is only about 1/4" gap. Even a small dent will have oil pickup issues.

Mtech2
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crank bearing clearances are too loose.

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NolimitZ32
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Car: 91 AG2 2+0 TTMT swap/E39 BMW 540i6/E53 4.6is Dinan S3
Location: Houston, TX

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Who did the rebuild?
What parts were used? (OEM or AM)
Damage to the oil pan will definitely cause issues
Check valves in the oil filter tree can cause issues
Are the turbos and oil lines OEM or AM
AM turbos will require a pill most of the time to control oil flow (not drown the turbos)
Don't depend on the factory oil pressure gauge, they are notoriously error prone even with a fresh out of the box sender

WhiskeyyMike
Posts: 11
Joined: Mon Mar 01, 2021 12:13 pm
Car: 1993 Nissan 300ZX TT

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It was an IPP Stage 3 build. And yes I know, you don't have to remind me about my bad decisions when I bought that 3 years ago... Oof. I wasn't planning on having a shop install it at the time or I would've just had them do the build.

The only real AM components inside the motor are the pistons/rods and bearings. All the other parts are OEM.
The turbos are AM as well. JWT550s. Having not installed the engine myself, I couldn't tell you much about the lines/pill/etc. But the shop that did it is pretty reputable and Nissan focused.

The pressures I gave were from a mechanical gauge, not the factory gauge/sending unit.

Like I said, the oil pan is pretty mangled, which very well could be an issue. Will be checking that when I get a chance.

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NolimitZ32
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Car: 91 AG2 2+0 TTMT swap/E39 BMW 540i6/E53 4.6is Dinan S3
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I've dealt quite a bit with IPP in the distant past and they have always been an extremely high end builder. They actually sourced all my build components and I used the same machine shop they use so unless they soured badly I would think they knew what they were doing. How did the oil pan get mangled? I'd say that would be your first thing to check/replace. I understand that you're not using the factory gauge right now, what I was meaning is if you want to see how it does under load go spend the couple hundred dollars on a good electronic oil pressure gauge setup and run that in lieu of a new OEM sender.

WhiskeyyMike
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Car: 1993 Nissan 300ZX TT

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Yeah I heard they were pretty good, so I was pretty comfortable ordering from them at the time. The shop I took it to, Dynosty in Louisville, Ky said they've had very mixed experiences. They've worked on some engines that had no issues whatsoever, and they've worked on some engines that they had to send back to IPP multiple times. Also it would appear IPP no longer builds the VG30.

And okay I see what you're saying with the gauge. A much better AM pressure gauge setup is definitely on the list. I'm not sure how the pan got so mangled. Previous owner issues I suppose. Appears to even be welded in some spots. I'll definitely check that for sure. Shame it's such a pain to pull it off.

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NolimitZ32
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I did not know that IPP stopped dealing with VGs. May be something there. I used to be one to prophesize about the difficulty of working on Z32s until I started getting deep into my 4.6iS. Z32 is a cakewalk in every regard in comparison to any V8 BMW of any vintage.

WhiskeyyMike
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Car: 1993 Nissan 300ZX TT

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Yeah I just noticed a few days ago. Still selling parts for the VG, but nothing built like they used to. First time anyone's ever said "cakewalk" and "Z32" in the same sentence right there.

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NolimitZ32
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It helps that I've pulled the engine 4 times now on Z32s throughout the years. My record from running car to engine hanging above the car is 4.5 hours.

WhiskeyyMike
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Joined: Mon Mar 01, 2021 12:13 pm
Car: 1993 Nissan 300ZX TT

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I've only pulled it once. And frustratingly getting to the oil pan off is about halfway pulling the motor anyway. Hoping to get to it this weekend. The oil pan doesn't look completely dented inwards, but it's certainly deformed pretty badly and clearly had quite a bit of sub-par repair on it.

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NolimitZ32
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You can span a bar from strut tower to strut tower and hang the engine from it and then drop the crossmember from below.

WhiskeyyMike
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Car: 1993 Nissan 300ZX TT

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Only took 2 weekends but I was able to change the oil pan out. Cursory look appears to show no less than 30psi at idle at running temperature. Which I'm quite happy with. During a quick drive, the psi was getting up close to and maybe into the 60s but never fell below 30. This was using the OEM gauge with the brand new sending unit.

I have a new AEM gauge but didn't have time to install it. Coincidentally, where is the best place to run the sensor wire through the firewall? I was having a look and really wasn't sure where to run it.

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NolimitZ32
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Car: 91 AG2 2+0 TTMT swap/E39 BMW 540i6/E53 4.6is Dinan S3
Location: Houston, TX

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I've ran additional wires through the EFI harness hole by penetrating the factory grommet to the side of the main loom but you have to de-pin whatever wire you're running to make the hole as small as possible.

WhiskeyyMike
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Joined: Mon Mar 01, 2021 12:13 pm
Car: 1993 Nissan 300ZX TT

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Alright just as a "final" update for you guys - I got the AEM gauge wired in and everything all buttoned up. After about 15-20 minutes of driving, the car is at full running temp. I'm hovering around 25psi at idle and typically between 50-60 on decent acceleration. So it would appear the new oil pan was the fix after all. Very happy with that, thanks for the help!

Unrelated, put some new tires on the car to replace the old dry-rotting ones. Noticed a little bit of clutch-slippage on hard acceleration. Then, yesterday, leaving work, car's stuck in neutral. Clutch won't disengage to go into gear. The pedal doesn't feel totally dead, still feels like it has some pressure and resistance. Gonna bleed the clutch lines and hopefully that fixes the issue. If not, you may see another thread about that. Heh.

deemoetee
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Joined: Fri Sep 02, 2016 12:21 am
Car: 300zx

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Hey! Just reading up on your issues, and I have the exact same issue on my car.

Fully built motor with eagle rods, wiseco pistons, gt2860rs, all appropriate supporting mods etc etc.

Everything was running good for the 500 mile break in period and everything was good on the dyno up until 6500 RPM where I lost all oil pressure. It was 0-10 psi at idle and around 20-30 at 2k rpm. Was experiencing the exact same issue. Although, I was hearing a very distinct " whine " that goes up with engine RPM. It almost sounded as if the oil pump was cavitating. Pulled the motor, cut open the oil filter and didnt see any metal chunks out of the norm. My oil pan was dinged and the pick up had a small piece of RTV in it but other than that, nothing out of the norm. New pan and new pick up in hopefully starting the motor up again soon within the next week or so. First suspicion was oil squirters, since I know thats a common issue with wiseco pistons, after inspection they were all in tact, 2nd suspcion was oil pan/pickup which have been replaced. If the issue still persists, my final conclusion is going to be the Mains.

Sorry to revive a thread but just wanted to see what your opinion was.


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