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VQ35 Oil Consumption

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I bought an ’03 Pathfinder recently with the VQ35 engine. It has 87,000 miles on it. To make sure its prepared for a life with me, I've been performing all the periodic maintenance. I don't want to assume that it has been treated kindly. I began reading the following forums as part of this exercise.

http://forums.nicoclub.com/zeroforum?id=37

http://www.npora.ipbhost.com

The first thing that stunned me was the reports of power valve screws being ingested and causing damage. While reading that material, I came across posts talking about high oil consumption. The truck I bought was low on oil when I inspected it. Now I began to wonder if this might be a problem with my vehicle. Hmmm, high quality import?? Now I understand that lots of folks are having oil consumptions problem with the VQ35, regardless of vehicle.

Important Note: I have no idea what the oil consumption was on this vehicle before I bought it. The previous owner said it didn't use oil. Considering it was 1 quart low the day I bought it, it DID use oil. I just don't know how much or the reason for it.

I tore into the engine today to check the power valves. Fortunately they were all present and accounted for. They were tight too!! However, I noticed what I believed to be an unusual amount of oil film in the intake manifold plenums. There was an actual puddle of oil in the left rear area of the upper plenum. The area in the upper plenum above where the PCV port is located was amber from oil spraying up. A lot of oil was definitely getting drawn into the PCV circuit. Why????

In researching this, I came across this thread.

http://x.nissanhelp.com/forums/pathfinder/1117-2002-pathfinder-oil-consumption.html

Andre's explanation gave me hope, "Could it be this easy?!".

After pulling both the upper and lower plenums, I removed the valve cover. I was pleasantly surprised to see a clean valve train and cams in good shape. There was no sludge. At least there were no signs of oil starvation or infrequent oil changes here.

So, the prescription is to replace the right-hand valve cover, Sounds easy enough. Being the curious guy that I am, I was not satisfied with just fixing the problem. I had to know why oil was getting trapped in the baffles. Inquiring minds need to know.

After several hours of studying this today and making a valiant effort to clean my cover, I think I solved the puzzle. In retrospect, you don't want to do what I did. Just go buy a new cover. However, this little story will explain why replacement is necessary. If you don't agree with my conclusion, let me know. My E-mail addreess is at the end.

I think the baffles exist for one purpose, to separate the oil mist from the blow-by gases before they are sucked out the PCV valve and into the intake tract. The baffles need a drain so that the accumulated oil goes back into the engine. There is an oil drain port on the low side of the cover. I’ve pointed it out in figure 1. The opening in this drain is very small and it stands to reason that it would clog. I’m not sure why Nissan engineers designed it this way, but there must be a reason. Making the hole larger might keep it from clogging again, but it also might introduce other problems.

Figure 1

This drain gets clogged with junk that settles out of the oil mist. I’ve been trying for hours to get all the dirt/carbon bits out. I will eventually get most out, but what a job!!

I’ve been using mineral spirits (paint thinner) and then filtered out the particulates before reuse. Figure 2 shows my filtering setup, pretty crude but it works. Figure 3 shows the stuff that’s coming out. I’ve used many coffee filters tonight. When you start, the cleaner will be quite dirty and the filters will clog quickly. It's important to filter your cleaner. If you don’t filter out the suspended particles, you’ll never know when you cover is clean.

Figure 2

Figure 3

I put the cover in a large shallow container; I use cat litter pans for such things.

I found that the following steps gave me the best results.

  1. Put on nitrile gloves to protect your hands.
  2. Remove the PCV valve.
  3. Hold the cover horizontal, bottom side up, with the drain nearest you. The PCV port will be on the right. Plug the PCV hole with your right index finger.
  4. Holding the cover with your right hand, pour the cleaner into the two ports shown in figure 4 until they are full. then slosh it around for awhile. Then invert the cover and drain. Keep repeating this process. When you run out of mineral spirits, filter the dirty stuff and start again. Eventually the drain port will begin to flow. If you hold it at an angle, like it sits on the engine, you'll find that the drain will dump the mineral spirits for a few seconds after all the other openings have drained. This is what made me realize that it was a drain for the baffles. When you no longer get crud coming out, then it’s probably OK to reinstall. I lost count how many times I filled, agitated, and drained the cover. Eventually particulates stop appearing in the cleaner and the filter doesn't clog as quickly. You'll know when this happens.

Figure 4

There was a lot of junk in the baffles. Even after cleaning, the recesses inside the cover are covered with a film of sludge that will not come off except by scrubbing. You have to assume if the visible parts are coated with that stuff, so are the baffles. The mineral spirits flow nicely out the drain port now and it comes out clean.

Post write-up thought: After thinking about this whole thing, I suspect that oil loss occurs first due to the baffle drain being clogged. If people never check their oil, then damage results and then the oil loss is due to both the baffles and the damage. This is just a guess though. You should start a lifetime habit of checking your oil at every other fill-up.

In addition, I think frequent oil changes will prevent the baffle drain from getting clogged. The drain clogs due to solids being separated from the oil mist. If your oil is changed every 3000 miles, there will be a smaller amount of suspended solids in the oil and there won't be as much to clog the drain. Oil that is changed every 5000 miles will have a larger concentration of suspended solids and they might clog that drain more quickly.

Summary:

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