Just finished up a head gasket replacement on this reman motor ran less than 100 miles. Head lifted due to incompetence and poor assembly from the machine shop that sold the motor. replaced every o ring and gasket with oem, including gallery gaskets. I did the job in car, so I avoided removing the upper oil pan. After starting the car, it runs good and has oil pressure upto spec across rpm range. Once oil comes upto temp, however, oil pressure drops dangerously LOW. Verified with a mechanical gauge : 3-6 psi at warm idle.

Past 1k rpm, pressure resides within spec.

I am stumped. Changed oil weights to 10w-40 in hopes of it being related to bigger bearing clearances with the reman, no luck… oil light will still come on at warm idle.

Does the upper pan need to come out to diagnose further, since it’s the one part I didn’t install myself that could be causing this issue? Are oil pumps or the pick up tube known to go bad? Any chance it could be the O rings between the upper pan and block? Or should I start with looking over my work behind both timing covers?

Or Is it not even worth trying to diagnose, considering how poorly the motor was assembled. Should I just send it as is, maybe throw some lucas in it?

 

First, I'm deleting the duplicate post you put in the "Feedback and suggestions" forum as that's not where this query belongs. You'll get more suggestions via one thread. Next, when you bought this remanurfactured VQ from a local machine shop, did they offer any kind of warranty? Have you contacted them about this (and other) issues? Depending on where you live, why not pay to bring in a local Nissan tech to examine your engine build? it's hard to speculate on what the oil pressure issue is from behind a keyboard- you need a hands-on inspection to determine where the fault(s) are. But DO NOT "send it as is" and waste the shortblock when it seizes.

 

Hello, thank you for the reply. I apologize for the duplicate posts, I am relatively new to the forum and still confused on how to navigate everything. I couldn’t figure out how to delete the duplicate post.

Some background:

The motor was purchased from a different state, Arizona, while I reside in NJ. The motor was purchased almost 4 years ago, so any warranty or legal action is impossible at this point.

When this motor was first put in the car, a timing issue was found. Took some serious bickering with the shop to get them to pay (or at least help) for retiming the engine. I did not know how to work on cars then, so a shop handled everything, from putting in the motor to retiming. The machine shop paid $1100 out of the $3800 that was due for retiming.

Once fixed, I drove the car home, and found myself overheating. Towed it back to discover the head gasket was blown all along… or the shop failed to bleed the coolant.

Machine shop stopped answering my calls… I was out of money at this point. About a year later,
out of anger in looking back at the situation, I took it upon myself to replace the head gaskets myself despite never working on a car before. Very ambitious and Im still not sure what came over me. Took months of research and work. The results of my efforts is what you read above. I am quite confident in my work as I was extremely meticulous and double checked fsm as I went. I have every EM diagram memorized by heart.

Any attempt to contact the machine shop is futile at this point.

Similarly, to bring in a tech would require thousands of dollars as diagnosis requires a deep dive into internals. I imagine they would come to a similar conclusion and want to remove the upper pan or timing covers to diagnose further.

 

It's possible the Oil Pump ate some metal cornflakes and isn't able to hold pressure, I mean the engine had bad timing and a blown head gasket from the start based on the history you know of. Only other thing I can think of is there's a failed seal somewhere in the oil circulation system. I assume the engine was a used core from a salvage yard? Mileage unknown & history unknown apart from what you've already discovered. If the timing had jumped, then it's likely the engine had been beat on hard, potentially overheated at some point, or oil-starved.

It's up to you at this point. Continue sinking more time/money into it which would require a teardown of the bottom end for inspection and essentially re-do all the work up to this point. OR find a better replacement longblock to work with.
Does the engine have any bottom end noises? Knocking etc? Even with the lower oil pressure, how is it running?
Cheers!
-Icer

 

Hello!

If I’m being honest with myself, I would rather not spend any more time or money on the car… It has drained quite a bit from me. Dropping the upper pan would require more tools (cherry picker or engine support bar to drop the subframe) and parts. I can do the job, but I could also misdiagnose along the way and end up wasting even more time. I’d be more willing if I knew, exactly, what my problem is. At the same time, I also don’t want to destroy the motor if my issue is as critical as I think. If it can get me at least 10k miles, and audibly notify me to park it before sending a rod, I am willing to accept the risk. But I doubt that’s how it’ll go down. I’m a bit stuck and unsure what direction to take.

The motor sounds perfect. No noises from bottom end, even at operating temp idle, despite oil light coming on. The lowest my oil pressure dips is to 3 psi at idle, measuring with the mechanical gauge (unsure of accuracy).

Could taking it for a moderate drive help dislodge some debris in the pump, or help my symptoms slightly? It has yet to be driven linger than 5 miles since finishing my work. I did find some metal debris in the pick up tube I chocked up to being from before the reman, since I hear no noises, maybe the oil pump is indeed clogged. I took some pictures I will post it in the following reply as it just deleted my previous attempt to reply when I tried to attach.

Or could piston rings failing to seat properly, from not breaking in yet, affect oil pressure?

Thank you.

 

This is what the piece in the above pick up looked like once I pulled it out:

 

I don't think your oil pump is clogged, but if metal fragments passed through it, it would score up the sealing surfaces leading to decreased pump efficiency and pressures. Oil pumps are precision machined components, much like a turbo. Even a small scratch or chip in the rotor or walls can cause pressure losses. I suspect there is something else happening here though. That large metal piece pulled from the pickup could be bearing material from the bottom end or possibly journal material from the heads (cam journals).

To solve this mystery, you would need to do a complete teardown, I can't think of any "shortcut" method to give you definitive answers beyond that. Since it sounds like you don't want to invest the extra time/money into a full teardown, I say "send it!" and plan for a long-block replacement in the near future or simply ditch the entire chassis and move on. If I had to make an educated guess at this point, I suspect you have a wiped out bearing or journal on the crank bleeding off pressure. If not the crank, then the oil pump itself is the issue.

Most engine lubrication systems flow from the pump in the following order... 1st crank main + rod journals, 2nd piston squirters, 3rd cylinder heads (cam journals), 4th also cylinder heads (rockers and/or lifters). Somewhere along the way, you're losing pressure. As a side note, the oil filter is actually 1st in the sequence off the oil pump, however under heavy loads (high pressures & flow), the oil filter's bypass valves opens to prevent oil starvation.

Cheers!
-Icer

 

Thank you, Icer. I appreciate your time and advice.


I shot a call to the machine shop that made the motor. Unfortunately, they no longer have any documentation on the core.

They assured me, however, that they don’t have the time to take apart an oil pump to be reused. They stated they always replace them. Whether or not that is true, considering all my issues, I’m not sure. Especially with how the upper pan looked after such little use. Looks like it was never even washed!

They recommended raising oil weights, even though they said clearances are within factory spec, and adding a quart of Lucas.

If it were destroyed bearings causing the issue, wouldn’t I have seen a slight pressure increase with the 10w40?

I have yet to throw out the old oil filter that was originally ran before this work, I will cut into it and inspect for any more debris.

I also did not remove the oil pick up tube during all my work. Maybe it is worth checking; I will drop the lower pan again and remove that, inspect it and torque it to spec. I see there is no gasket used or sold for these pick ups, can I put one anyway, just to be safe? Would black RTV work or is that a bad idea? Maybe sealing surfaces aren’t perfect anymore causing air to be sucked in?

If no issues are found with the pick up:

I will replace this cheap stp filter I put on with a nissan oem filter, fill with 4 quarts synthetic (I currently have conventional for the break in) 5w50, and top off with the Lucas treatment. After which, I will run the car for as long as possible, ignoring the break in period I’m technically still in. I will disconnect the connector from the pressure sensor, cause I don’t need that negativity in my life. I will update the thread if/when it blows up.

I will also try and make the hour drive out to my tuner. I only fall under oil pressure spec when under 1k rpm; I will ask him to raise the idle to 1k to compensate. Past 1k I see great values, per fsm, and shouldn’t be starving anything.

I will never give up on this car lol at this point it is out of spite for whatever forces are keeping this dream from happening. If it blows up, it’ll get a used engine next time around though (I learned my lesson), or I’ll try my hand at building a stronger VQ.

Best,

 

Sooooo… my money was on clogged pickup tube … but, looks like I lost …

Conway may chime in … and I believe he had this issue back when dinosaurs roamed…

But how confident are you that you installed the ~10mm orings between the timing chain case and block (I think, it’s late, and Im exhausted) and in-between the timing chain case shells?

And assuming you didnt take off the upper oil pan then the two orings that seal up the oil pump should be in-place.

I know its a massive pain in the berries but consider renting / borrowing / facebook market placing a hoist and a stand and re-doing this outside of the car… I’ve done this many times and I cant imagine how difficult this would be inside the car.

 

Hello and thanks for replying!

I am sure I installed the larger two O rings between the rear cover and block. I actually had to redo my rear timing cover cause I messed some things up on my first try, I won’t bore you with the details (not relevant). In doing so I purchased all new oem o rings from Z1, since fsm recommends replacing after every disassembly, and threw the ones I just bought in the trash. A total of 6 if I remember correctly. 2 on each head and 2 on the block.

I also installed the 2 between the front and rear covers, as well as the 2 collared o rings and the weird rings that go on the intake cam sprockets.

I have no experience working on cars prior to this, but I did my best and took a ton of time researching. I also was aided through the process by a friend on Reddit, Phoenix, may God bless him.

Regardless, you are right. It could be those O-Rings, maybe they fell off during assembly or got pinched since I didn’t follow Nissan’s recommendation of removing the upper pan when pulling the covers. This “what if” is part of my problem. It could also be the oil pump without inspection, wiped out bearings, like Icer suggested, etc. I have no way of knowing without, “potentially”, a complete rebuild of the motor that could end up as deep as a replacement of every single bottom end bearing. If I had an inkling on what my issue is, I’d be willing to fix it, but I’m left in limbo without anything to go off. It is a guessing game without at least both covers off to start elimination.

An engine hoist is a start, but I may end up needing a crank shaft, along with other gaskets and parts. Considering the quality I received the motor in, is it even worth the investment of both my time and money? Researching alone and gathering the confidence to do a lot of this is mentally taxing in its own regard, especially with life’s priorities in the way. Im sure I COULD fix my issue with enough time, but It could end up exceeding the cost of just throwing in a used engine, time and money wise.

I hate the thought of ruining a motor when it could be something as simple as an o-ring… but it’s the way I’m leaning. I’ll continue to sleep on it.


Best,

 

Yep, the factory arrangement for the oil pickup tube doesn't use an O-ring or RTV. If your pickup is undamaged (no issues with mating surfaces), then I would leave it alone. If you use RTV, there's a chance excess could break off and get into the oil pump. I'm referencing an 06 (Revup VQ35DE) FSM and for the rear timing case cover, I see 2-small O-rings per cylinder head (#20 in diagram) and 2 larger O-rings near the center left of the block for the main galleries (#19). There's another O-ring shown in the diagram (also #19), but I think that appears to attach to the block near the oil pump, it's not clear. It might be for the timing chain oil-jet/squirter gallery or for the timing chain tensioner gallery, which I assume are both built into the rear cover. The Revup oiling system is different for the intake + exhaust cam phasers, so you may not have the same cylinder head O-rings. But if one of these O-rings was missing, I think you would start to notice an oil leak, the perimeter RTV sealer around the rear cover is not meant to hold up against high pressures.


Rear timing cover O-ring locations.


Thinking about this some more, the oil pressure sensor is located right after the oil pump. Meaning your pressure readings (from the sensor or analog gauge) are reading direct pump pressure before hitting any engine components in the circuit. I'm thinking maybe the O-rings between the upper pan and oil pump are either damaged or missing. I'm really thinking the shop who did the work on this engine missed something or made a mistake somewhere. This is all just speculation on my part, but you could have damaged/missing O-rings, or a broken/damaged oil-jet somewhere in the circuit.

Using thicker oil is a band-aid measure in my opinion, but it's better than nothing.
-Icer

Here are some diagrams from the FSM for the various components.


Visual oil lubrication diagram

Lubrication circuit flow chart

 

So I can rule out my rear cover O-Rings, since I have no external leaks? That third O-Ring, furthest to the bottom, I believe is for the upper pan. I have no recollection of it, and it was not in the front and rear cover gasket kit I got from Z1. I have the 04 DE model.


If an upper pan O-Ring is truly missing, wouldn’t I see low oil pressure across the rpm range, not just idle? And wouldn’t I hear noises since those rings hold pressure to the main oil gallery and piston squirters? Also, wouldn’t oil temp be irrelevant since oil would internally leak anyway without an O-Ring? I see good pressures for a solid 20 minutes, until oil temp reaches equilibrium; at which point my pressure will drop dramatically at idle, but remains at spec past 1k rpm. I feel a missing O-Ring would have me seeing symptoms across the RPM range, and would be more extreme.

I saw no noticeable pressure change with 10w40, can that rule out bearing clearances, or any wear?

I have no codes for vtc or timing related, surely that means can rule out all the front cover O-Rings since I am getting sufficient pressure to those systems, at least enough to not throw a fault.

Can my symptoms eliminate any suspicions?

In theory, I see Oil pressure working as a garden hose would when restricting the exit. Volume (oil pump and pick up) and restrictions to the flow.

Here is my suspicion:
With my pressure readings coming directly from the pump, before any restrictions internally, and is reading low, that implies an issue with the pump/pick up and their sealing surfaces (or an issue before oil reaches pump), right? So a volume issue, rather than a restriction, due to viscosity decreasing (from temp) and pulling in air due to poor sealing. The sealing surfaces of either the pump or pick up would cause these symptoms, if my understanding is correct.

Given the lack of VTC codes, my thinking is that even if the pump/pick up is providing reduced oil volume, the restriction through the bottom end system is still enough to maintain pressure and allow oil to make it to the top end without starvation. Do those with gallery gasket issues also experience vtc issues, since they lose top end oil pressure? If so, that would be a major clue… but haven’t come across it.

Are we sure any internal restrictions are irrelevant to oil pressure readings at the sensor? How do Z owners discover their oil pressure issues otherwise (infamous gallery gaskets)? Im left quite confused about this concept.

Also, when gallery gasket issues are encountered, is the issue only at idle, or do they noticeably lose pressure at higher rpms too?

Can an issue with the oil cooler system cause oil to be getting too hot? That would cause viscosity to get too low, decreasing pressure as well. Is the housing something I can/should take apart and inspect?

Thank you,

I should have some time this weekend to take the lower pan off, and inspect from there

 

Against better judgment, I just took the car for a short drive. Got it up to temp, and the oil light didn’t come on. With the AC on (i dont have the ac belt on, so i think it just turned fans on) it put the psi right around 14 at idle. Maybe my symptoms are getting better or weren’t there to begin with.

Im considering getting a second mechanical gauge. While highly unlikely there is potential, for both my sensor and the gauge I used, to be receiving inaccurate readings.

Edit: Nevermind, oil pressure dropped once I got home and checked it. The picture above is after driving for approximately 8 minutes (I let it warm up already before driving) , shutting it off, letting it cool for 20 minutes, then turning it back on and snapping the picture.

Here is what the pressure looked like once I got home. No oil light, but it’s definitely too low:



I still question the accuracy of my readings, however, as the difference seems very drastic, no way the oil cooled down that fast when sitting to cause that big of a difference between the two pictures.

 

Hey Fairman,

I concur with your observations...
1st pic pressure looks normal.
2nd pic pressure seems abnormally low.

To answer some of your other questions, I guess any "leak" along the pressurized oil galleries/feeds would impact the sensor reading right off the pump gallery in the upper oil pan. Since the pump is driven directly by the crank, flow volume is dynamic and managed by RPM and the regulator valve in the pump + relief valve system built into the oil filter + oil cooler (since too much pressure can also be bad). Since pressures climb to "normal" levels above 1k RPM, then I think it's logical to assume your bottom end components are getting enough oil. Perhaps when the engine work was done, they clearanced crank main + rod bearings on the more "loose" side of spec? Who knows without an in depth teardown.

Here's an idea for you. Continue driving the car and monitoring things. I'm not sure how many miles you have on the engine oil since the last change, but I would take a used oil sample and send off to a lab for analysis, how many mi you go before taking the sample is up to you. Personally, if I was worried about serious damage, I would take the sample within 500mi of driving, maybe even less. But if I felt confident that everything is "ok" then I would drive 3600mi before taking the sample. I would also cut open the filter and see if there's any signs of forbidden glitter.

I use Blackstone Laboratories for my UOAs, you can get free sample kits mailed to you. Short of tearing down the engine, I think this is probably your best bet on getting some real data into your engine's state of health.
Cheers!
-Icer

 

Thank you, Icer, for your time. I’ll look into having the oil tested, I appreciate the suggestion

Here is what the oil filter (from before I did my work) I just cut into looked like. Approximately 50-100 miles on this oil and filter




Here is what some of the oil looked like that I drained from the filter. Very silvery and glitter is present but I believe it’s nothing short of normal break in material. No chunks or nuggets were found:





After inspection, I want to conclude bearings are not the cause of my problems as I would have the material to show for it.

I will remove the current oil filter (post HG job) that is on currently as well, to cut into and compare to the other, as well as to replace with a nissan filter to eliminate that as another variable (cheap stp filter). I will do that tomorrow.

Before dropping the lower pan, I decided to wait to buy another mechanical gauge to double check my readings on the current oil viscosity. I am still questioning accuracy and would like to rule it out definitively.

If I were to put in a thicker oil, and see an improvement to pressure (up to spec) , do I conclude larger tolerances and move on with my life or that i’ve simply swept my problem under the rug by forcing a higher gauge reading? How thick should I try? Im on 10w40 right now.

 

I personally wouldn't go above a 5W-50 weight oil, but that's just my personal opinion. STP filters are built very cheap and I wouldn't trust them for long-term operation, but should be fine for short term break-in period usage. The filter media has been known to collapse or separate from the glue joint.

Yes, there is most definitely glitter present, but as you said, this might be normal break-in material. The oil is also very dark for only 50-100mi on it. This doesn't surprise me much seeing the state of the upper oil pan in your photos. This engine has a lot of deposits in it. I'm a bit shocked that a professional shop rebuilt the bottom end and never ran the block or upper pan through a parts washer, that's standard practice for any reputable builder.

Here's how I see things. Continue putting miles on it, IF something isn't right, then likely damage has already been done and you likely won't hurt it any further. But, if everything is good, then perhaps we are just over-thinking things. Once the break-in period is over and rings are seated, you should see the glitter clear up.

Given the amount of deposits inside the engine, I would strongly recommend using Valvoline Restore and Protect once the break-in period is over. That stuff works magic, but it doesn't happen overnight, it takes 15-20k mi of constant use to get the best results for major deposit removal.
Cheers!
-Icer

 

Hate to be the one quick to jump to alternative solutions, but you can pick up a DE for about the same as the gasket kit. I think your options are a full engine removal and tear down if you are attached to this engine, or a remove and replace. The tools to do an engine swap and the tools to do a gallery gasket jobs are basically the same plus a engine hoist. You can probably pick up one of those from HF or marketplace for super cheap.

 

I bought another mechanical gauge, with a claimed +/-2psi of error, to triple check my readings. I also replaced the oil filter with Nissan’s prior my tests.

Here is my pressure at cold start:


Here is my pressure at fully warm operating temp (about 30 minutes of running)



I forgot to ask my friend to grab a picture of the psi reading at 2k rpm, but he read 37 psi.

I did not want to test the 6k rpm spec reading.

Some inaccuracy was present in the original test I did, but not by much. Psi fluctuates between 8-10 psi at idle with this gauge that I believe to be more accurate than the last. I definitely have a problem and have finally accepted it, grief is a ***** lol. Still a bit relieving as my original readings were extremely low.

I think both of you guys are right. With my updated readings, I think the motor will be okay with thicker oil, maybe for a while. The inevitable will happen, however, as I definitely have an issue with 3 gauges now telling me there is an internal leak.

Since I’ll need a hoist to begin fixing the issue, why not just take the opportunity to replace the motor. JDM motors look like a great deal, and may end up costing the same as a full rebuild; if considering time, can be much cheaper.

Factory spec, less headache, and who knows I may end up getting my moneys worth from this current motor proceeding with this plan.

I’ll keep the thread updated.

Thank you everyone!