Hey guys - first post so hopefully I'm doing this right. I bought a 2003 G35 with 71k last year. This year I found this board and so I can't help but modding here and there. First thing I did was put a K&N drop in and changed oil out with Mobil 1. Noticed an instant 2 MPG gain (not sure if that's in my head or not).

Anyway, this weekend I put in a Motordyne 5/16th spacer and noticed that my plenum was really dirty (brown to black deposits). I cleaned with a lint free wipe as best I could. My question is why was it so dirty? Should I be worried? The guy I bought the car from definitely was not into cars, but had all the service records and it doesn't look like he ever put in decent anything but conventional oil and any new part that he had installed came from a shop that specializes in tires (Tire King here in Raleigh). Also, he told me he never used premium gas either. Good news is that the spacer made a huge difference in mid range torque which is what I was looking for.

 

Did the previous owner ever change out the airfilter?

 

It must have been changed within 20k. When I removed it, it still had some yellow to it. It wasn't that dirty. FWIW, the butterfly valve looked fairly clean, I figured that would be black if dirty air was getting in.

 

When I pulled my motor at 130k, it looked like this....
Top of the Plenum

Inside the Plenum, I had oil deposits

Took the center cover off and there was a small pool of oil.


More pics of oil deposits





But I must say, mine drank a quart per 3000 miles. So I see where it was going.

 

yup...that's about how mine looked. maybe not quite THAT dirty, but it appeared to be well on its way. I didn't know what to use to clean it so i just used a dry wipe. Is it a cause for concern? How can I keep it from getting worse?

 

I wouldn't say it's too much of a concern. Mine ran perfectly like that to 130k miles. I would say it's prolly BETTER to clean it out but with our motors consuming a little oil, you are gonna get that in the Plenum, but with your spacer, maybe the air will circulate better and take the extra oil into the cobustion chamber and burn it off instead of leaving it there.

 

Seafoam really helps clean that up.

If you have it off the car, you can use several things to clean it up as well. I used Simple Green and got most of the stuff off. Let it sit for a little while and use a brush to agitate.

 

As for your question on why the plenum is/gets dirty see the following thread:

https://g35driver.com/forums/engine-...catch-can.html

 

awesome - that's well within my novice abilities. I actually got an iso thermal kit, but i chickened out when i realized i had to take the lower plenum off.. haha. I'm going to try this out as soon as I can.

 

If you decide to open up the plenum again
you can use Gas with a toothbrush or Brake cleaner
and get rid of all the deposits you have in there.

And then add the oil catch can so you can minimize the oil vapors that go back into the plenum

 

Since i think a Z-tube will be my next mod, I may as well take another hour and open the plenum up again to truly clean it out once I have the OEM tube out. Thanks for the advice.

 

The residual oil and deposits are part of the design of the PVC system and isn't not a problem. I wouldn't bother cleaning it because it's not impacting performance.

 

........ Partially true, but if you're like most of us it's not a great idea to have all that oil residue inside your plenum ending up on your valves....get a catch can. Easy fix is installing a Home Depot compressor catch can, cost is like $5= and you might get a tea spoon of oil between changes. At least it's not inside your engine where it doesn't belong.
Gary

 

i've been reading the DIY catch can threads and there definitely seem to two schools of thought on the subject. i've not decided what i'm going to do yet, but i do agree with the logic that says any oil where it shouldn't be is a bad thing.

after i changed my oil, i refilled the oil quarts with the used oil from my last oil change (approximately 5k miles). I was surprised to see that I filled the 5th quart only 1/4 full. maybe that's normal?

 

^That's fairly consistent with what I've experienced.