I've begun working on my upper intake manifold, thinking I have
developed some problems with the EGR plenum. Well, after removing it
and not seeing the immediate signs of this failure, I believe I have a
Please see these pics:
You can barely see, but in the upper left portion of the lower intake
manifold, I have enough oil pooled to cover one of the bolts that hold
the LIM on.
I will be replacing the UIM and PCV valve, as well as the gasket/seal
and properly torquing the bolts.
But where do you think this oil came from? Do I have another leaky
gasket? Should I remove and degrease the LIM, or just soak up the oil
and clean the gasket/seal part of the LIM?
Thanks for any input!
Just soak up the oil. What you have is not that abnormal. You probably
make a lot of short trips which creates more moisture in the crankcase vent
system. This moisture takes some oil mist with it through the PCV system and
into the plenum. This is an area the customer isn't supposed to see. You
might reduce the oil mist amount by switching to a 10W30-40 instead of a
5W30-40. The pictures you took look about the same as the few I've changed.
Make sure you take the O-ring from the old PCV. Sometimes it sticks in
If that bolt and the one diagonal from it don't have the threads
sealed, the manifold vacuum will pull oil up past the
bolt/threads and it will pool.
Worked on a 3800 a few years ago that had the lower intake
gaskets replaced at a dealership, within a few months, the car
ran like crap, in the process of diagnosing it, I removed the oil
fill cap while the engine was running, huge suction (that
shouldn't be). Pulled the upper intake, the bolt you highlight
was just laying there across the low spot in the manifold. None
of the lower manifold bolts had any sealer or Loctite on them.
(draw your own conclusions)
I'd replace the lower intake gaskets. They fail just the same as
all the other GM V engines except that the coolant passages are
towards the center of the manifold, not on the ends so there is
less chance of seeing traces of coolant leaking thus heading off
a much larger repair.
On the upper plenum throttle body picture, see the three oblong
holes adjacent to the EGR hole?
Probe from the EGR hole towards the outside oblong holes with a
pocket screwdriver, you're looking for any signs of the plastic
softening or having broken away.
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