[gruffybear]

During inspection today of my 98' Duratec (92,000 miles) pulled air filter and noticed a small trace of oil inside the flex (accordian) tube right where the rear vent hose plugs in. Is this normal? I started to wonder about oil entering the throttle body so I pulled flex tube off and looked inside the brass flapper and on the rear side of the flapper there was a black oily film. I've seen black soot on the inside of a throttle plate before but it wasn't oily (wet). I'm wondering if this is normal or if this is a sign of an interior engine problem. Anyone have any ideas? Should the throttle body be "pulling" oil from the vent tube?

 

[NateNBeckie]

You can thank the crankcase ventalation for that. On your 'Tec you have 2 tubes coming from each valve cover into the intake tube between the MAF sensor and the throttle body. When the engine is above idle and the throttle plate is open, it is not only sucking air from the air box, but it is also creating a vacuum from the crank case, sucking oil vapors into the intake. This is meant to be like that for emissions reasons. Over time with heat this causes the black, oily soot you are describing. It will probably be all over the inside of the intake manifold and the secondary butterfiles.

What you are describing is completely normal. The only way to take care of it is to disconnect the two tubes going into the intake, combine them and run them to a "catch can" somewhere below valve cover height, then vent the catch can with something like a K&N breather filter. This of course is technically illegal because it is not good for emissions, but it won't throw any codes and no one will know unless you tell them or they see it.

One of my projects this weekend is to take care of that crud. Take apart the manifold, clean it and the throttle body up, and clean up the secondary butterflies.

-Nate

 

[gruffybear]

Nate, thanks a million!! I wasn't sure if the oil vapors were meant to enter the throttle body. Keep me posted on how you clean you secondary butterflies. I'd like to do this as well but not sure if I'll have to remove the lower intake or if they can be cleaned with the lower intake still on engine. Good luck!