MaxOctane

I remember when my air filter had nothing but dirt and bugs in it.

Over the last 16 months or so I've noticed the bottom corner of my air filter now gets black with what appears to be oil. It's almost like blow-by, but I was under the impression that the PCV valve hose goes directly through to the intake, bypassing the air filter.

I started noticing this about 16 months ago. About 12 months ago I changed to a K&N filter (not expecting the problem to go away), and now the bottom of my K&N filter gets black with oil.

I religiously change the oil every 3K miles, or 3 months whichever comes sooner with Mobile1 10W30 fully synthetic (I know it's overkill). Anyway, I cleaned out my throttlebody the other day and I was floored by how much crap was in there. There was a ton of black gunk that I cleaned out of that thing. Anyway, I was thinking the two problems might be related, however I wanted your opinions of what it might be. After cleaning out the TB, it definately idles better, and I think it run's smoother, but it's probably just in my head.... Anyway, your opinion is valued. Thanks.

P. Samson

The normal flow of breather vapors is from the crankcase and upper engine areas through the PCV valve (or metered orifice) into the intake plenum or manifold. But under high engine loads at or near WOT this flow reverses and dumps the breather vapors into the intake between the air filter and the TB via the vent hose from the front camshaft cover. This happens because there is little or no vacuum in the intake downstream of the throttle. Also blowby increases with high compression pressures and adds to the amount of breather vapors. After engine shutdown this oily residue can still be in the intake between the filter and the TB (thus the gummed up TBs) and in your case maybe this residue is running (draining back) through the MAF into the filter. Is it a manual tranny car? This tends to be seen more on manual tranny cars. Is the car parked with the left side really low? With your frequency of oil changes I'm surprised your oil is so black. On my 2000 auto the air filter has always had some black stains at the bottom closer to one side. This is on both a stock paper one and a K & N. They are never really oily though.

ghostrider17

iTrader: (6)

I've had this same issue on my 6spd 2k2 since day one.
I'm still on OEM filters, and I change these religiously....and I do go WOT quite often.
I haven't cleaned my Throttle Bodies yet, but I Imagine I will in the near future.
I'm running Mobil1 as well, but don't change any sooner than 5k now.

Seems to be normal to me!

Interesting topic. Thanks.

gr

Matt_01SE_20th

iTrader: (1)

you can stop this with an oil catch can i think

P. Samson

Further to my comments above re oil in the intake...... this is one disadvantage of using synthetic oil. It is more "sticky" than regular oil which tends to make it gum up things like the TB and intake runners more than regular oil. Unfortunately we have to live with oily vapors being dumped into the intake system of our cars. I had changed to a synthetic oil on one of my previous cars and it later developed an emissions test failure problem. (NOx) I finally had to remove the intake plenum and manifold to mechanically remove coke and carbon from the undersides of the heads of the intake valves. During this process I found the inside of all the intake plenum and manifold runners to be coated with a layer of sticky oil. Plus the usual areas that I had routinely cleaned before... the TB and the downstream inlet ducting was not just coated in the usual oily residue which had always been easy just to wipe off, but it was now coated in this same "sticky", oily film. I have not used synthetic oil since. Anybody who "abuses" a car should probably use synthetic but for a daily driver I'm not so sure. I know the NASCAR boys and the dragster guys have gone to it. When they blow the bottom end out of an engine now, it takes longer to clean up the track because of the synthetic!!

MaxOctane

Thank you for your replies.

Yes I do have a manual tranny. When I used the paper filter it was the black "stains" on one of the bottom corner that I noticed. Now that I have a K&N filter, it appears these stains get mixed in with the air filter oil to make it more of a liquidy sludge. I wouldnt say that my air filter gets "soaked" in oil, at least not to the point where the oil is draining back into the air filter because the car is parked on an angle. Also, the black stains are on the OUTSIDE of the filter...the side of the filter that catches all of the dirt and bugs. Is there even any oil vapor on that side of the filter? Even the air/ oil vapor seperator is on the throttlebody side of the air filter, so I would think if any extra oil vapor is going into the filter it would show on the opposite side of the filter.

The thing is, it never did this at the beginning. I bought my 2k maxima 3.5 years ago with 28K miles on it. I switched to mobil1 synthetic. Never had the black stains on my air filter. I usually change the oil myself, however I took it in for the 60K mile maintenance in September of last year. They were going to do an oil change, so I brought my own mobil1 synthetic with me. I told them to use my oil because they didn't carry mobil1 synthetic. Anyway, the morons still used regular oil (non-synthetic), despite what I told them, and despite that I had a 5-quart jug of the oil sitting in the passenger seat! I get my car back, and sure enough the same full jug of oil was sitting in my passenger seat. Amazing....simply amazing....how stupid can they be....? Anyway, it was several hundred miles before I could switch out the oil, and ever since then I started noticing the black stains on the air filter. I don't know if the dealership-oil-change thing is related, but it was about the same time that I noticed it. I usually don't drive the car very hard at all. Only every once in a great while will I pull to 5K when accelerating on the highway.

It makes me feel better that others have the same thing, however it makes me wonder because at one point it was not doing it.

I also understand about using synthetic for those who "abuse" their cars....One might consider it abuse when they hear how many miles I want to get out of my engine.............

ghostrider17

iTrader: (6)

Not to doubt what you say -- but I've NEVER heard of this issue before.
It certainly sounds logical, but I can't believe that this could be a widespread downfall to upgrading to a fully synthetic oil.

Do you have any imperical / documented data to back-up your theory?
Seriously, if you have any data to back this up - i would be interested in reading it.

Your posts are very informed and insightful, please don't take my dissention as a flame!

gr

P. Samson

I just looked at the K & N filter that I had in my Maxi (auto) for only about 2000 miles. It has already a backened dirty area on the outside surface low down like you are taking about. This filter was new from the factory and the car was only driven on paved roads with relatively little dirt and dust. Are you sure that what you are seeing is not just normal dirt and crap impinging on the filter particularly if it was slightly overoiled. When you mix dirt and oil you end up with a blackish sludge it seems to me. There is no way that oily vapors can get into the intake upstream of the air filter on a stock intake. I know you said that you hadn't noticed it when you first bought the car so other than replacing the PCV valve I don't know what to suggest. If you are really concerned I suggest a Nissan PCV valve P/N 11810 31U 00 about $12 US I believe. But as I said before it is not uncommon to see oil in the intake between the filter and TB particularly on manual tranny cars. (Not just Maxis.)

MaxOctane

Well, forget that I have a K&N filter that has filter oil in it. Back when I had a paper filter I had the same thing happen. On one bottom corner of the filter it would get dark with what appeared to be oil. It was almost as if there was a spot on the air filter where oil vapor was being fed through the air filter. I don't know if this is what is happening, but I know it wasn't always doing this. It's probably normal, however I wondered if anybody knew of any reason why this was happening....

P. Samson

On the synthetic oil deal I would still like to use synthetic but I am just leary about it due to my previous experience only with the aforementioned car. (I worked in an industry where we used synthetic oils out of necessity.) I have no data or info and I only used one brand which it turned out probably at that time anyway was not the best choice. (Castol) When I took the aforementioned car with the emissions issue to the "AirCare" emissions testing Lab for help in troubleshooting my problem the engineer that ran the place casually asked what oil I was using. When I told him that I has been using Castrol Syntec his eyebrows raised. The lab shop technician who was originally a Ford tech. told me that he had been using the same oil in a suped up Mustang that he owned and after dealing with a lot of emission issues in his job at the AirCare lab, had switched back to non synthetic. There were some trends that they were seeing indicating that the synthetics MIGHT be causing some issues but he was somewhat vague. It was after I had ripped apart my car to access the intake valves and noticed this stickiness in the whole intake system that I decided to go back to non synthetic. This was just my experience with synthetics and I am sure that most people using it really have no problems. I also "abuse" my cars because I tend to keep them a long time ('81 Rabbit....340,000 mi. no engine issues) and I expect long life from my cars.

P. Samson

I am convinced that you have nothing to worry about. I just found the paper filter that was in my Maxi when I bought it with about 25000 mi. on it. I don't know the mileage on this filter but it has a blackish stain (skunge!?) on the outside convolutes just like you saw on yours. It looks quite clean otherwise. I know this car had been regularly maintained by the old guy that owned it before me. When you think about it the heavier, more dense crap will tend to end up closer to the bottom areas of the filter. I can imagine some of that oily, slimey stuff (road spray in the rain) that comes off the roads with normal traffic flow can get into the intake. Roads with the old cars, diesel trucks etc. add to this mix. The roads used to have that black band running down the center of each lane. It is not as obvious now with the newer vehicles that don't leak as much but some of that still has to be there.