Greetings -

I have a 2003 Maxima SE, 110,000 miles. All stock, with synthetic (Mobil-1) oil and filter changed at least every 6000 miles. It's currently burning about 3/4 quart per 1000 miles. After doing a bit of digging, I see several theories regarding potential causes for oil consumption:

-questionable piston ring design
-problems with the cat immediately downstream of the manifold regurgitating into the cylinders
-PCV valve sludged up

First question: is 3/4 quart per 1000 miles considered "excessive" for this car with these miles? I can't find a spec in the service manual re: acceptable consumption, but the rule of thumb I've always heard is 1 quart per 1000 miles before it's worthwhile to do something about it.

I'll be selling this car this spring. I'm aware that the cat theory is controversial, and even if it's the real deal, it's not worth my time/money to fix that. Likewise if the rings are worn. But the PCV valve? This sounds like it might a reasonable time/money investment, if there's a chance (nothing's certain, I know) for chopping the oil consumption. If I can cut oil consumption, that might raise the value of the car to potential buyers.

I'm aware of what a PCV valve does (directs blow-by from lower area of engine back to intake manifold to be burned). Can someone explain how a sludged-up PCV valve can result in oil consumption?

Have people here actually had good success in cutting oil consumption by replacing this part?

 

I have 0 expierience on the matter but the DEK I recently purchased was from an oil burning vehicle.

I pulled the intake manifold and there was about 1-2 cups of oil in it.

So I deleted the PCV system (from the intake)... and viola.... No more oil burning....

Try installing an oil catch can, may help your PCV problem there, that's 1/3 down.

You also failed to mention Valve Seals, apparently that's the big thing people fail to mention are failing valve seals will cause the motor to nom some oil.

So I gave you a solution and gave you a problem... Does that mean I helped?

 

my 02 with 125,000 kms had high oil consumption. The front valve cover gasket was leaking oil so I replaced both front and back valve covers and gaskets. Front spark plug tubes were fine, but the back spark plug tubes were full of oil. Do your self a favour and order some 04 valve covers.

 

Exactly how did u delete the pcv system ??? Did u throw a code ???

 

Plenty of threads my good sir.

 

Ok thanks. Time to research.

 

You describe a problem with leaking oil, not burning oil. My Maxima does not drip oil on the garage floor at all. What will replacing the covers] do for me?

 

If leaky valve covers are not a contributing factor to oil loss, then replacing will do nothing. However, I can't think of a single 5.5gen maxima owner who has inspected their rear valve cover and NOT found it to be leaking at cylinder/plug 5 (rear and furthest right).

So, replacing the rear may not do anything else but protect that plug and coil pack from damage due to swimming in oil constantly. But for that reason alone, its a good idea to get the rear replaced. For the record, I don't get why people go ahead and replace the front if its not leaking, guess peice of mind. But the front is not prone to the leaking as the rear is.

 

Mine wasn't leaking any oil on the floor. The front valve cover gasket was seeping on to the exhaust manifold and burning off. The 5th generation maxima's are known for leaky spark plug tubes, so I ordered vc's and gaskets front and back. I had two tubes in back vc full of oil. I've read on this site that the oil in the tubes leaks down the spark plug and burns off, I have no idea if that is true or not, but I had the same problem as you. "oil consumption with no visable leaks on the floor"

 

the 04 valve covers were $31 a piece, and the back cover comes with a new PCV valve. While your there it's a good time to replace the plugs.

 

I just took a quick peek with a flashlight, and didn't see any obvious signs of leakage. Should I be able to spot something without any disassembly?

The service manual describes the procedure for removing the entire cylinder head, and so of course it requires removal of intake manifold. Looking under the hood, it sure looks like this will be required for removing even just the rear valve cover. Is that the case? or will I be able to to replace the rear valve cover without messing with the intake manifold?

 

You will want and need to remove the intake. Very simple, should be able to pull it in about 10-15 minutes - while smoking a cig and finishing off your drink of choice.

I doubt you would be able to see any visable signs of oil. With that said though, maybe you're part of the not yet affected 1% of owners.

 

Is it necessary to actually replace the old covers with new ones, or is it enough to reseal the old covers?

 

You have to replace it if its leaking in the spark plug tube. Replace with 6th gen cover.

 

OK, I ordered a new rear cover+gasket, plus collector-to-manifold gasket. Will install all and see what happens.

Thanks for your help, everyone.

 

I swapped out the rear valve cover today. Sure enough, tube #5 was full of oil.

So where has the oil been going from there? The top surface of the valve cover didn't have any evidence of leakage; it seems like the coil unit was forming a decent seal with the valve cover. I've had high oil consumption for maybe 15,000 miles now, so there are a few quarts of oil that have fled the scene somehow, but even with the intake collectors out of the way, I can't see any obvious signs of oil seepage.

You're a better man than I; it took me a good hour to pull all of the various tubes, hoses, and zip tie anchors and get the collectors removed.

 

welcome to the 5.5 gen family. You can replace the valve covers with 6th gen like I did (they help but wont stop the consumption). I was told its the piston rings. Just keep an eye on the oil and fill it up every once in a while, I've gotten used to it. Or you can do a 6th gen engine swap or rebuild the current engine with new rings. Other than that you have to just deal with it.

 

Was there any oil inside your intake manifold when you pulled it out? Best place to look at is right behind the VIAS valve that's bolted to the side of the intake manifold with the three 12mm bolts. Remove these to check inside the IM, if it's coated with oil, chances are your piston rings are shot, creating blow by that ends up getting sucked inside the intake manifold through the PCV. Chances are replacing your rear VC will not solve the oil consumption... It's most likely an internal issue (piston rings or valve seals).

 

There was some oil in the lower intake collector (and I think in the upper too). I would expect some oil in the intake tract even in a healthy engine, but I'm not sure how much is indicative of a serious piston ring problem.

Valve stem seal problems would increase oil consumption, but shouldn't result in oil getting into the intake collectors. I guess the logical conclusion is that I've got a piston ring problem.

Should a ring problem bad enough to burn 3/4 quart per 1000 miles result in a noticeable drop in fuel economy? Highway MPG is as good as ever (29-30 as indicated by the instrument cluster).

The spark plugs on the rear bank looked reasonably clean, i.e. they don't appear to be getting fouled with oil. Haven't changed the front plugs yet.

 

Mine burnt a quart every 500 miles, and still got great gas mileage, and there were puddles of oil in the IM, not just a thin film...

If the intake valve seals were leaking, could the oil make its way back in the upper IM somehow? Reason I'm asking that is because I had installed an oil catch can for about 10k miles and it barely captured any oil, just a few mL...

 

Has anybody tried installing this VQ35DE PCV valve delete breather kit from project import? http://projectimport.com/store/350z-...-breather-kit/

 

I think replacing the pcv valve would help the engine as far as tune up goes. Im in the process of doing my rear valve cover on my car, then replace the #5 plug and coil while im in there, and also get a new intake manifold gasket.

 

Yeah, that's what I was thinking to. I'm just wondering if it'll fit. It says that it's for any Nissan or Infiniti with a VQ35DE engine. If nobody's got it, maybe I'll get it and be the test dummy.

 

Oil consumption will never go away and continue to get worse.

Find a Nissan Murano VQ35DE engine, remove the precats or get headers and call it a day

 

I already have headers. I just figured that it would keep the oil from getting into the intake manifold and being burned out by the pistons.