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Oil in my intake manifold

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barks944

New member
I'm found a notable amount of oil in my intake manifold when doing some maintenance yesterday. The rubber boot that connects the AFM to the throttle body had oil in the ribbing and the rubber where the breather hose connects to the boot is perished. The evidence would point to oil coming through the breather system. I have removed the breather pipe from the boot and sealed of the hole. As far as I am aware the crank case breather system goes to the manifold is to reduce emissions so it should be fine to let the pipe vent to atmosphere.

Any suggestions as to why oil might be coming up through the breather system? I thought maybe the crank pressure was high but I checked cylinder compression and its showing over 150psi on all 4 cylinders. The consistency across the cylinders would suggest to me those readings are good. I'm not sure how much pressure to expect though. The following calculation suggests it is spot on:

Compression ratio = 10.6
Atmospheric pressure = 14.696psi

14.696 * 10.6 = 155.7776psi

Tom
 
That sounds OK if all 4 cylinders are about the same.
When was the last time you have taken the throttle body off?
You will get some build up over time due to the crank breather running back into the intake.
Best bet is to run the breather pipe into a catch tank(old 5l oil bottle works well).
 
There is a connection from the sump to the intake, somewhere ahead of the throttle body. This is so a venturi effect is created whereby air being sucked into the engine sucks air out of the sump to reduce the pressure in the sump and increase the pressure differential across the piston rings and improve piston ring sealing against the cylinder wall. There is an air-oil separator (AOS) which is supposed to do as its name suggests, but inevitably some oil finds its way into the intake, so i'd say what you've found is 15 - 20 yrs of oil accumulation. It is certainly normal to find oil in the intake system - whenever i've removed any of the intake pipes the insides are coated with oil. I'm not sure if the AOS allows some oil to be sucked into the intake system by design or not. I can't imagine oil mixed with yor fuel/air misture is going to do your emissions any good, but then again you might need some oil in the mixture to help lubricate the cylinder walls - i'm not sure. Anyway, I wouldn't bother too much as long as your oil consumption is normal.
 
Just pulling up a old thread i found whilst checking out a query about my inlet manifold.

I recently took my air induction pipe and throttle body off while trying to get to some sensors, I saw oil and crap built up in both like the OP found so i gave them a good ole clean.

My inlet manifold was pretty caked too so I'm just wondering what the benfits off taking it off and cleaning it would be if any?

A little bit of me doesn't want to disturb it as sods law will strike and i'll end up snapping a bold or nut causing me ten times more work.

If do do remove it what would the best way to clean it be? Take it to a pro to have it soaked in a chemical tank etc?

 
It collects in the intercooler too. There is some suction in the intake system, which you will lose if you vent to atmosphere, not sure how much suction is generated though.
Tony
 
Once the manifold is off it is relatively easy to clean, there are also several pipes that run under the manifold that are easier to check / replace with it off.
A coating of oil probably won't be affecting it much though
 
Cheers buddy, thanks for the reply.

Looks like its a job I'll do at some point them just to ease my OCD and i'll pay attention to other bits first.
 
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