Hi everyone, I have an oil pressure problem with my 2005 Nissan 350z VQ35DE and the motor that is currently in the car has driven around 150.000km and has 10w60 oil. I have driven it for the past year and a half with this oil without any problems but recently when I send it to a mechanic for a replacement of the rear main seal because it was leaking and also got a new clutch and flywheel installed.

But since i got it back there is a significant drop in oilpressure mostly noticable at idle. Then its barely above 0psi. Around 1k its 30psi and from 3k onward till like 5k it hangs around 60psi but the pressure bounces a bit. I added some photos of the psi at different rpm's.
The oil pressure sensor has already been replaced and also oil pressure has been confirmed with an external oil pressure tester.

First i thought about the gallery gaskets altho unlikely for a DE, so i bought a replacement set but when changing them the original ones didnt show any sign of leakage they sealed perfectly. I still replaced them but that didnt fix the problem.

Some other suggestions ive gotten where faulty oilpump or crankshaft bearings but havent had the time to check them out because when i take something apart might aswell replace it. But that would be a bit expensive unless i know almost for certain that it will help.
So if you have a suggestion what it could be please let me know!

 

I would cut open the oil filter and inspect for any metal contamination. if it has bad bearings that would be evident. otherwise I would think its likely an oil pump, wouldnt hurt to check the oil pick up tube for debris either.

 

We didnt find any metal flakes, also checked the oil pickup and no debris or chunks. I was thinking or oil pump itself or the o ring that hasnt been properly installed by the previous guy that worked on the car. Thanks for the suggestions!

 

with no metal flakes the bearings are probably fine then. if whoever did the rear main seal took down the upper oil pan and those o rings werent replaced with it there is a good chance that is a cause for concern. if they are a half decent shop/mechanic you would think they would replace any seals and o rings if thats the case. I would have a conversation with the shop and they may be on the hook for the labor to get to the o rings anyway.

 

Yeah probably the o rings

 

Something interesting is definitely going on. No reason to be running oil that thick unless you're running a built motor with loose clearances. Might be time for a teardown and refresh.