Crankcase Breather Vent

[Gauthier]

Should you be able to see oil vapors coming from the crankcase breather vent? While idling, if I close off the tube with my thumb for a second and then release, I get a blow of vapor that you can feel five inches away from the tube outlet. Does this sound excessive? I noticed this when investigating a drone that just started at idle and around 1600 - 1800 rpm. At idle, the sound seems to build up and then down repeatly. It seems to be emanating from the oil pan area, but I'm not 100% sure of the exact location. It’s as though something is resonating.



I'm new to diesels and am not totally familiar with the sounds that should be expected, so I investigate sounds that have changed. This is definitely a new sound, and I haven't noticed the oil vapors before. I have checked the crankcase breather tube before and the ID always seems dry.

 

[jimnance]

I'm on my fourth Dodge CTD. As I recall, my '95 had noticeable vapor coming from the breather. It never caused a problem, and the truck served me well for 100,000 miles before I got my '99.



The breather is there because every engine will have a small amount of blow-by past the rings. It will never be a perfect seal, and the crankcase will pressurize if there is no place for the gases to go.



I'd suggest that this is not a problem unless you are seeing a good deal of oily discharge. This may indicate excessive blow-by.

 

[DIESELMAN]

Unlike a gas engine, the manifold is always under pressure and never a vaccuum, therefore the crankcase must be vented to the atmosphere, instead of using a PCV valve like a gasser.



Don't plug the vent, it only takes 5 - 8 psi to blow out seals, then you'll have oil leaks.

 

[rbattelle]

Don't be too concerned with the resonant sound you hear either. If the idle is steady, things should be okay. There are so many frequencies in the engine noise, it's easy for your brain to pick out a few of them and make a nice little "tune" that you think is resonance.



Also remember that blowby, and hence flow out the breather, will be higher until the engine breaks in.