the_dood

Hello all.

So before i dive into the the main topic, let me please begin with this:

About two months ago i was at a light waiting for it to turn green, and i noticed my low oil pressure light come on, on the dash. At the time, i thought it was a low oil LEVEL light, i have since been mistaken. Threw in about a quart and a half and all was good. Let me also say that before this low oil pressure dealio, in my 5 years of owning my Z, ive never had an oil pressure problem, but i am aware of the Z burning up oil like a champ, i usually keep a mental note when i should check the oil but with work picking up and life happening it slipped my mind. The oil level before i put some in was a 1/4" above the end of the dipstick but i dont know how long i was driving around with low oil before the light came on.

Ok, so as of now, the last two months when driving i have NORMAL oil pressure on the gauge. Right around 40 to 60psi give or take depending on my speed, usually 60-80 mph. As soon as i come to a complete stop, and idle, my oil pressure gauge falls to what appears to be 5psi (right around in that area) and SOMETIMES the low pressure light comes on. If the car is all warmed up and running hot (not bad hot) and ive been driving for a while it will come on, if its only been maybe 20min it will idle at i would say 15psi. All of this is with proper oil level, midway on the L to H scale.

I checked to make sure the oil cap was on tight, it is. I wanted the communities help to rule any other obvious solutions before i deem the oil pump the problem. I dont have a good grasp on the mechanical working of the Z oil pump. I dont know would wear on the pump is the oil level was low.

Any suggestions would help. Sorry for the length of this bad boy, i just want to make sure i leave nothing out.

Edit: I have an 03 Touring Z with about 146k miles, 6 speed man.

StuLax18

iTrader: (4)

What RPM is your idle usually at? I get that light sometimes if the RPM's did real low before it dies and I put the clutch back in when slowly pulling into a parking spot where I want to move up but not hit the curb. It will stay on too even after I go into neutral, unless I tap the throttle to raise the RPM's back up and it will turn off before I shut it off.

the_dood

I wanna say at 500-750rpm. I can tell you honestly that my idle speed hasn't changed since the day i bought. I did however think about that, if i barely tap on the gas when im idle the light goes away the oil pressure go up a tick, then falls back down to 5psi and the light comes back on.

StuLax18

iTrader: (4)

Ok, yeah it wasn't exactly an apples to apples comparison, but I was just trying to get at the idea that the light can come on but it doesn't always mean there's an issue.

BALDTIRES

I wounder if you have a bad sending unit. could make a gauge read low....

the_dood

Also forgot to mention the sending unit has been replaced. The reason I replaced sending unit was because the oil pressure gauge needle would tick back and forth when it gets up around 60psi. It also occasionally would get stuck on 120psi. I would tap the gauge then it falls back down to normal. I now think the gauge is a fault here. Maybe the little gears are worn out OR maybe the new sending unit is faulty. I just don't know.

KornerCarver

iTrader: (2)

It is also possible you have damaged your bearings with the incident of low oil level. Damaged bearings result in larger clearances which in turn would lower the oil pressure at idle. It might be wise to have a mechanic take a look at your car.

the_dood

Would you mind explaining which set of bearings would be the culprit?

KornerCarver

iTrader: (2)

That would be the bearings on your crankshaft. That is where the oil pressure reading is picked up. Again, I would strongly urge you to have a qualified mechanic look at your motor.

tcode

iTrader: (7)

Oil pump doesn't create oil pressure. It simply just flows the oil through the system. Bearing clearances and oil passages creates pressure. With larger oil clearances oil pressure drops.

Main bearings on the crankshaft and rods bearings, if worn, creates a scenario like yours. Of course, it's a good idea to check oil pressure with trusted device before dismantle and rebuild the engine.

the_dood

Would a qualified mechanic use or do to test it out? Let's say I buy or borrow a pressure test kit to accurately test the engine oil pressure and it reads fine but the light still comes on, what would I do then? Or for worst case scenario the test kit DOES show low pressure and it is a bearing problem, is that a major engine overhaul or a weekend project? I'm a mechanically inclined person.

Would bad or worn bearings give a low idle pressure AND a driving oil pressure or just a low idle pressure, because as I stated before, the oil pressure while driving is fine it's ONLY while I'm at an idle.

the_dood

I also wanted to ask if what if this whole low idle oil pressure is just a coincidence at the same time the oil level was low and maybe there is a small leak out of the head gasket area? There some oil residue and stuff down there. Maybe the seal isn't 100% causing a low idle pressure. I just want rule out the easier fixes before I think about the whole engine coming apart.

jhc

did I miss it?...
how old is your oil?

the_dood

Little over 4k miles.

Turnstien

Take it to the dealership they could give you a ideal with in a hour I bet for less then a 100 bucks Nissan could pin point this or a decent dealership save your self the stress. Good luck

rcdash

iTrader: (18)

Run a thicker oil and bump up the idle (nissan can bump it 100 rpms with few button presses on their consult device). Both will serve to increase oil pressure at idle. If you've damaged some bearings (and they're probably a bit worn at that mileage anyway) you can try to prolong life with a heavier weight oil. I would change the oil to a 10W-40 or 15/20W-50 (if you live in a warm climate). If you can see little metal particles in the drained oil then you need an engine rebuild.

the_dood

I'm going to change the oil and put in what you suggested along with a new oil filter and see how that goes for now and cross my fingers. Maybe the filter is clogged up with some debris or something. If the problem persists than if the price is right at the stealership, I'll have the take a look, hopefully tell me what the problem is, and maybe it's something I can take on myself and a buddy.

the_dood

Quick question, the oil pressure gauge AND the low oil pressure light on the dash do they both get the readings from the sending unit or does the gauge get a physical connection to the engine oil pressure and the low oil pressure light connected to the sending unit?

Bigsyke

First, i would do this:

Time how long it takes to build oil pressure on a cold start. If it takes more than 1 second for the oil PSI to shoot up to 90psi, you have a problem.

What oil filter part number are you running? You can get a "wrong" one for this car. I bought a purolator classic and the base wasn't concaved enough. The M1-110 seems to be a solid performer and the proper base, and the Fram XG6607 being nearly as good, if not better (for cheaper). Make sure you blow into the base of the oil filter before purchasing to test the ADBV.

I would grab a magnetic drain plug. Hit up walmart and grab a jug of Rotella T6 and 1 32oz bottle of Marvel Mystery oil and a Fram XG6607 or XG7317. If that doesn't help increase pressure in about 1500 miles of light driving, get ready to pull the pans. You could check the engine grounds for safe measure. The magnetic drain plug will allow you to see how much shavings are being run through the engine.

Generally you should be at 60psi at around 2500-3k rpms. You may need to check the pickup tube and make sure its attached firmly and not leaking.

I caused a very similar issue by running krank vents. Oil pressure was 3psi at idle, but normal cruising. Crankcase vacuum doesn't press the oil through the pump. When I removed the krankvents, I was back at 25psi @idle. Maybe you can remove your oil cap, and check your idle PSI.