oil buildup / leaking out of valve cover breather

shine · September 25, 2005, 03:12:34 PM

if you use a pvc and no breather you will blow oil out the dipstick. why did they run breathers before pvc's ?

47convert · October 02, 2005, 12:16:00 PM

All of the suggestions are good, but I can't get over the paper towel thing - I think I'd cut the top off an old pair of socks (color co-ordinated with your motor of course) and slide that over the breather. Not a fix but it'll keep the oil from running everywhere.

shine · October 03, 2005, 11:56:26 AM

pvc's were the first smog tech. they took the breather tube off and replaced it with the pvc and a vent. you build pressure in the crankcase by rotating mass and compression blow by. it does not suck thru the breather. why vent a trans ? or rear end ? a well vented motor will not blow oil from main seals . you must have a good vent even with the pvc. it relieves excessive presure in the crankcase.

enjenjo · October 03, 2005, 12:11:51 PM

Quote from: "shine"pvc's were the first smog tech. they took the breather tube off and replaced it with the pvc and a vent. you build pressure in the crankcase by rotating mass and compression blow by. it does not suck thru the breather. why vent a trans ? or rear end ? a well vented motor will not blow oil from main seals . you must have a good vent even with the pvc. it relieves excessive presure in the crankcase.

The trans and rear end are both vented also. And the air does get sucked into the breather on a PCV system. On most OE systems, the breather is another tube into the air cleaner that pulls air for the PCV makeup.

shine · October 03, 2005, 12:32:26 PM

ok, your pulling vac on the crankcase so how is oil coming out of the breather ? we ran vents on both valce covers down to the collectors on our race car just to keep oil inside. without them you blow oil out every seal. you get a lot of blow by even on a new motor. you can not depend on a pcv alone.

tomslik · October 03, 2005, 01:46:21 PM

Quote from: "shine"ok, your pulling vac on the crankcase so how is oil coming out of the breather ? we ran vents on both valce covers down to the collectors on our race car just to keep oil inside. without them you blow oil out every seal. you get a lot of blow by even on a new motor. you can not depend on a pcv alone.

either too much blow-by or it's under wfo all the time.
(no manifold vaccum under wfo,therefore no pcv operation)

enjenjo · October 03, 2005, 08:29:43 PM

As Tom mentioned, on a race car, you don't have much vacuum. On our race engines, we ran a vacupan stup similar to what you describe. On a normal engine, a PCV is enough.

A couple things to remember, all PCV valves are not created equal, they are designed to open at a vacuum level that is correct for that particular type of engine, so it is possible to have the wrong valve, and it won't work properly. Second, you should not have both the PCV, and the breather on the same valve cover, the other side may see enough pressure to force oil out. Third, on a long high speed run, it's not unusual to have a bit of oil vapor out of the breather. If it's enough to drip, that is too much, but it is normal to get a bit of oil around the breather. A sock slipped over the breather will keep it from getting all over the engine, or if you want to be fancy, they make outerware covers for them from foam.

shine · October 04, 2005, 06:18:27 AM

at idle the pcv is closed. at hwy speeds it is open to evac the air/oil vapor mix . the pressure in the crankcase will find it's way out. be it thru a breather.pcv or your main seals. i run moon valve covers with no holes and put a 90 deg moon breather on the dr side front by the alt. even after long hwy runs they dont lose oil from the breather. the breathers are large and foam filled.
enjeno's right about the valves. they can have a direct influence on air/fuel mix if incorrect. causing rough idle and lean mix.

purplepickup · October 04, 2005, 09:41:57 PM

Right or wrong, this is how I stopped mine from seeping. I've raced it quite a bit, drove a bunch of miles over 12 years and it's still there and working fine. The foam was just a piece of packing foam I had laying around. I soaked it in gas for a while to see if it melted. Since it didn't I cut a rectangular chunk and stuck it in the breather. I cut it a little big and it just formed to the inside of the tube. I haven't had any leaking, either around the breather or anywhere else.

Pope Downunder · October 06, 2005, 10:44:05 AM

Quote from: "purplepickup"Right or wrong, this is how I stopped mine from seeping. ...snip ...

This excellent picture confirms what I have observed from experience.
Under different conditions air (or crankcase fumes) will flow into, or out of, the breather.

The PCV is calibrated to the engine, as noted in the former posts. One of the functions is to prevent backfires from igniting the gasses in the crankcase, so they are also a 'one-way' check valve.

When there is high manifold vaccuum, like decel, or idle the PCV will be fully open. Somewhere between there and WOT it will be closed (unless there is a positive pressure differential).

Under these load conditions, fume will naturally flow out of the breather, (or into the air cleaner). Over a period of time, or sustained high load, even a healthy engine will produce some seepage and fumes from there. Some of these breathers will actually get saturated with oil, especially with an unbaffled valve cover.

On a rod I had in the eighties, I had a biggish cam (low vacuum) and a Holley 600DP on a single-plane manifold. This, with the stock PCV configuration, was not good. It used to have a big flat spot, and blow some oil vapours into the air cleaner. When I got it dyno'd, the tuner said the PCV was like a vacuum leak right under the carby, so it would be difficult to tune the stumble out. So, he knocked the guts out of the PCV, and plumbed it to the clean side of the air filter, and fitted a breather cap to the other side valve cover. The effect was dramatic, the throttle response was great! To control oil accumilation in the air cleaner, I made a little cage over the inlet barb and fitted a pad of air fliter foam inside that. That had to be rinsed out when doing a service. This system performed flawlessly for many miles, returning over 20mpg on a trip. With a mild cam, this sort of thing is not necessary, and the stock set-up would be better all-round.