When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I’m replacing my starter and when I removed my intake plenum and the second plenum, both seemed to have quite a bit of oil in them. The car runs well, doesn’t smoke and the AOS was supposedly replaced 3k miles ago. I have no oil consumption over the past 1k miles. Does this seem normal?
It’s a BMC filter. That is an oiled filter, but I would think the MAF would foul if it was letting that much oil into the intake tract…? Also, the oil in the plenums smells like motor oil for what it’s worth.
That amount is pretty normal. The AOS doesn’t condense all of oil, and with the airflow there the motor is “cool” and that’s where the aos receives vacuum. Some oil condenses and accumulates there.
All those oiled filters are pretty much good for beans ..... Put in a regular OEM filter and recheck .
if it was from the air filter your maf would be toast already. It’s from the AOS you can measure the crank case vac if your are worried about it but it’s pretty normal.
That amount is pretty normal. The AOS doesn’t condense all of oil, and with the airflow there the motor is “cool” and that’s where the aos receives vacuum. Some oil condenses and accumulates there.
+1
That amount of oil is fine and normal in the plenums. No worries. The Air Oil separator return line enters the plenum there and the vacuum can pull in oil mist from the AOS. That amount of oil would not come from your BMC air filter either. Although, what I would suggest is take that time to get CRC MAF electronic cleaner and give your MAF sensor a good spray and cleaning with that product every 6 months or, at minimum, once a year.
It’s a BMC filter. That is an oiled filter, but I would think the MAF would foul if it was letting that much oil into the intake tract…? Also, the oil in the plenums smells like motor oil for what it’s worth.
It is probably filter oil from the PO. That would be my first guess. I have had this issue a bunch of times because I commonly buy used cars with K&N filters or similar already installed. When you run your finger on it, is it red? I think K&N filter oil is red. IDK about BMC. If it is, then that is most likely the culprit.
Also, on turbo cars I have had, there is always blowby. IDK about NA cars but do people run catch cans on NA cars? On my turbo cars, I have really nice set ups to capture the oil blowby. I have had turbo cars for 10 years before getting my C2S, so I forget... In any case, someone mentions it above but clean the area and then either clean the BMC filter and make sure there is little to almost no oil on it and put it back in, or run a stock filter and see if the oil returns.
In any case, as mentioned above as well, if it hasn't caused any lights (i.e. MAF death or something), I would not stay up at night worrying but I would try to diagnose.
Thanks for all the replies! The oil is not red, it looks and smells like motor oil. It seems the consensus is that this is relatively normal. I’ve spent too much time over the last few days reading about DIY AOS replacement. I think I’ll table that for now, clean it out and continue to watch it.
I suspect you are getting a bumpy idle no? If so, clean the throttle body butterfly and all around it well. Use MAF cleaner or other simple solvent and a rag.
I also believe this is normal. Pulled my TB yesterday and had a little in there as well. No idling issues aside from slight NVH due engine and transmission mount upgrades. I have an IPD plenum and K&N filters currently.
01-24-2022, 12:18 AM
Oil in Intake plenum—normal?
