I have an 03 Coupe 5AT, 101k. There was seemingly no issue with oil burning until my last oil change made it quite clear. It had to have been low. So I checked after a week, still all the way at H. 2 weeks after that it's 1/3 down from H to L at about 1,200 miles. Does anyone know how much oil that is roughly?

Also, is putting oil in every few weeks a decent measure? I'm not trying to pay for a new engine for a 12 year old 100k+ miles car. $25 in between changes seems like a better option if it doesn't get worse. Not sure what else I can do, if anything.

 

Been through a lot of pain, "blood, sweat & tears", R&D, Trial & Error with my VQ35DE motor.
To save most of you guys time, I'll share what I've done and noticed from inspecting the VQ.

#1: Piston rings - seems to be the most probable and annoying cause, since the OEM rinigs have a light expander behind the oil scraper ring. For some reason Nissan changed them to these in '05. I ended up just buying a low mileage motor and building it ground up. (CP pistons, rings, Carrillo H-beam rods, pins, ACL bearings, ARP main and head studs/bolts, Cosworth baffle, IP billet girdle, etc.. Going TT)

#2: PCV valve - as @wechslerl said, it's best to have a catch can or breather setup in pcv valve port to regulate and remove fumes from the engine crankcase, and to alleviate crankcase pressure which could cause oil leaks or seal damage. (http://oilcatchcan.com/)

#3: Oil pump - most build shops all recommend switching to atleast the Rev-Up oil pump to keep oil pressure up and able to handle high rpm (7k)

#4: Head gasket - not often does a headgasket fail on these motors, but Nissan's new design with the VQ35HR's head gasket, helps cool the backside of the motor evenly. A small modification (grind 11mm deeper in block for water passage) is needed. I also recommend the Pathfinder Cooling Kit. Best installed with motor out. ( http://goo.gl/0T5mqN )

#5: Get a tune - keeping AF/R in check even after installing a few bolt-ons will really help the motor from running rich thus burning tons of oil

#6: Spark plug seals - I didn't have to change these, but have noticed a few owners that have had oil seep into their spark plugs. A good sign is when you're changing them, you'll see oil on the back sides of the spark plug. You can buy a whole valve cover gasket kit from here: www.rndfactory.com

Add longevity to your motor: If you ever decide to rebuild your motor, I recommend getting WPC Treatment - wpctreatment.com - they have the technology to harden important parts of your engine, bearings, and other moving parts while also decreasing friction with their surface treatment. A lot of good results are coming out of this treatment...check out this live test:
To all the other techies or guys/girls with more experiences to add, please do.

 

Hi all. Rising the thread from the dead
I've read several thousand messages and several topics related to OC problem within a week on this forum.
But I could not find the answer to the question:
is there the final answer, why the OC problem has occured? Should I consider drifterxG's answer above as the final reason?

Seems like my Skyline PV35 Sedan 6-mt, March 2005, (right-handed, Japan-imported) also has this OC problem with VQ35DE non-RevUp.
My related topic (created before i've read all of this):
https://g35driver.com/forums/intake-...l-burning.html

 

Part of it is the rings, part of it is the variable cam timing, part of it is the oil squirters spraying the bottom of the pistons. The VTC creates a very high vacuum inside the combustion chamber on the intake stroke during deceleration and the oil control rings aren't doing a great job, plus there's a HIGH volume of oil being sprayed at the bottom of the piston to cool it.

If you decelerate the car by downshifting the engine this makes the problem 100x worse since you're spending so much more time under extremely high combustion chamber vacuum.

The biggest culprit is the rings though. I've bottle honed and re-ringed a couple regular DE engines and the oil consumption went away. You can do a backyard re-ring for about $300, it's like $100 for head gaskets, use the Nissan Juke MR engine head bolts with ARP washers so you don't have to drill/tap the block (they have better thread engagement and are stronger than the OEM bolts, they're cheaper, but they are TTY like the stock ones so keep that in mind), those are like $125, and a set of cheap Hastings rings is like $50 through Summit Racing.

Obviously there's some extra tools you would need to do the job so that will increase the cost if you don't have them.

 

Thank you @cleric670 !
Due to differences between USA and Russian markets, I used other spare parts manufacturers.
As i mentioned in my post on link, I changed piston rings (OEM STD size), valve oil seals (OEM), crankshaft bearings (Taiho, STD size), connecting rod bearings (Taiho, STD size), engine gaskets (Victor Reinz).
Oil consuption now remains at 650 ml/1000 km (0,68 quart / 621 miles), 2000 kilometers (1243 miles) have passed after re-bulid.
Seems like now I have to open engine again, and bore short block to + 0,50, hone it, and install new repair piston kit (Teikin + 0,50), repair piston rings kit (Tanaka Piston Ring + 0,50) and new engine gasket kit (Victor Reinz again). Regarding to your message, I hope this will resolve the issue.
Also hope there is no need to change crankshaftt/rod bearings again.

 

First I would make sure you aren't getting your oil consumption from the PCV system. Temporarily plug off the intake tube and intake plenum ports and install breathers on the valve cover. Then drive for another 1000 km and see if the oil consumption went away.

 

Thanks for the advise, but sorry, due to my “business” english knowledge I don’t get what do you mean clearly 😣 Local translation difficulties…
Can you explain, please, somehow other way?
As i know, VQ35DE (non revup) has only one PCV, it is placed on the right side of the top of the block, and has the tube that goes to somewhere on the engine back side. So - do you suggest just to disconnect this tube from back engine side and leave it as is?

 

Ok the positive crankcase ventilation system (PCV) on the intake tube is a hose located between the MAF and the throttle body, it goes to the left side valve cover directly below the throttle body. There is a crossover tube that connects the two valve covers located at the front of the engine right below the intake plenum, it is accessible without removing anything. Lastly there is the final hose that runs from the PCV valve that screws into the right side valve cover, this hose goes directly to the front of the intake plenum.

How the system works, basically it sucks air from the valve covers back into the intake plenum, this air is metered since it's all contained after the MAF sensor. Blowby gas from the piston rings (combustion chamber) ends up down in the crankcase and needs escape somehow. Normally it is sucked back into the engine through the PCV system. The problem is there is a LOT of oil particles floating around in this air because of all the moving parts like the oil squirters, crankshaft, etc. It breaks the oil down into a very fine mist or fog and all this oil+air gets sucked into the engine as well. This has always been an issue with high revving cars, the faster you spin an engine the more likely you are to be atomizing oil into the air.

You can essentially bypass this entire system by plugging the two hoses for the intake plenum and intake tube by the throttle body. However the crankcase will continue to build up blowby gas pressure so you install little filters on the valve cover, or a vented catch can, or something.

Here's a picture of the PCV diagram.

 

Thank you.
So… Questions:
1. Seems like there is 2 oil catch can needed?
Why most of all installs only 1 OCC, like this?

2. Also, is this correct - PCV valve is installed only on the right side valve cover? There is no PCV valve installed before the hose that goes to intake tube?

Yesterday I just disconnected two hoses and inserted its ends into 2 bottles. Intake plenum + intake tube holes from these hoses were plugged. Will see… But I think my consumption caused by the issue with bad oil channel gaskets + this piston rings problem. And could be fixed with bottle honing only…

 

One catch can, between the PCV and the intake plenum, is enough.

There's so little air that backfeeds from the left side up into the intake pipe that it's not really worth the effort to add a second can. It's only sucking from that side during wide open throttle, so it makes sense for a very limited type of vehicle, not for a daily driver where 99% of the time you're under manifold vacuum that FAR exceeds the intake tube vacuum.

Usually it's drawing air FROM the intake tube, not pushing air into the intake tube.

 

I wouldn’t recommend the breather filters, highly recommend an eBay vented catch can over those. VQ’s can have a significant amount of blow by / crankcase pressure. Efficiency wise being connected is better as far as I read.

 

@cleric670 @Urbanengineer 650 km have passed after I’ve disconnected PCV system. Nothing changed. Yesterday I’ve left my car in a service for engine rebuild as I mentioned before.