Moisture In Intake Manifold

[vpetersen]

So I was in the process of replacing a bad fan clutch, and while I had the air intake hose off I peeked inside the the throttle body/intake manifold. I was a little surprised to see moisture in there. I do most mechanic work myself, but I need guidance as to what the symptoms mean. Does moisture in the intake mean the intake gasket is leaking? Blown head gasket? I guess I should have determined what the moisture is, oil/coolant. ...get back to you on that.

I don't have any trouble codes and the engine runs good, but there is a little steam/light blue smoke (can't tell which) upon start up, then after warm up the cat starts to clean it up. Any ideas??

...upon closer inspection, fairly certain moisture is oil.

 

[RonD]

Condensation is related to the moisture in the air, the temperature of the air and the temperature of the surface.

A glass of ice water gets condensation on the outside of the glass because it is cooler than the surrounding air.
Warmer air can hold more moisture, when the air around the glass cools down the air it can't hold as much moisture so it "condenses" on the glass.

Air being sucked into an intake is cooled, so the inside of the upper intake will be cooler than the rest of the lower intake which is warmed up by the engine heat.
When the engine is off moisture will condense on the cooler surface, inside the upper intake.
As the temperature in side the intake equalizes most of the moisture will evaporate back into the air.


Most engines have a PCV and also a Vent hose, the vent hose comes out of a valve cover(or oil filler tube) and runs to the air cleaner or air plenum between the air cleaner and intake.
Oil vapor does come into the intake this way, it shouldn't be excessive, if it is check the PCV.

When a cylinder fires the piston rings can not contain the full "blast of power", so some of this pressure is pushed past the rings and in to the crankcase, this is called blow-by, and is normal.
As rings wear out the blow-by increases, this is normal as well, but it can lead to excessive oil vapor in the vent hose and Blue smoke at the tail pipe.
If you remove the vent hose and you can pour oil out of it, a ring job may be in your future, if the PCV is not clogged.

 

[vpetersen]

Alright, looking all over the web gives me all kinds of answers...too many. Have read that it is normal, pcv valve, blow by, lower intake gasket sucking oil, etc etc. Guess I'll check compression and pcv valve, any other suggestions? Please and thank you!

 

[vpetersen]

Ron D, I wouldn't say its excessive, just a light coating. Condensation does make sense, because its 25 degrees outside. So, what I'm considering to be engine oil could be condensation mixed with oil particles being vented via the breather tube and or blow by. I'm still going to check compression though, because even though I don't think the moisture in the intake is excessive, I think that the start up exhaust smoking is a little on the heavy side.

 

[RonD]

When doing the compression test inspect each spark plug.
If you have coolant leaking into a cylinder the spark plug will looked "washed"(cleaned) compared to the others, because in a sense it is being "steam cleaned" every time engine is started.

Also check exhaust system for leaks towards the back, you don't hear these but they let air into the system when engine is off which leads to more water vapor to clear on restart.
Condensation occurs inside the exhaust system when it is off and cooling, which is why the pipes rust so bad, usually from the inside out.

 

[adsm08]

A light blue haze when starting could just as easily be valve seals, which won't show up on a compression check.