Excessive crankcase pressure or not?
Apr 17, 2004, 09:59 PM
#1
Excessive crankcase pressure or not?
OK. I have been doing some research on the topic of crankcase pressure/blow-by because I had my dipstick pop out during a dyno tune and make an oily mess all over Shiv's shop floor. Apparently, this is a common problem in the DSM world and not only for those with worn/tired motors. Here are the circumstances: oil level was high-almost over the top of the overfill line; was running 5-30 mobil 1; I had removed my stock valve cover-to-intake blow off line and installed a little catch can-like device that Mitsuorder designed here: https://www.evolutionm.net/forums/sh...+own+oil+catch Finally, Shiv doesn't baby cars on the dyno: he works them very hard to make sure his tunes will stand up to real life racing/extreme situations - so if something wierd like this was going to happen, it is no surprise that it happened while on Shiv's dyno.
While on DSMTuners, I found a vendor who made this comment in a post two years ago:
You might want to keep the hose connected to the valve cover & intake. W/ it connected the suction from the turbo sucks the extra crank case pressure out of the valvecover... ever notice your dipstick popping out? Try reconnecting the hose & watch how it misteriously doen't pop out anymore.
I'm not sure how the valve cover breather can effect crankcase pressure (pressure offsets pressure???) but I'm happy to report that my problem only occurred once and I have tortured it to see if the dipstick thing could be induced again and the answer is no. I have returned my car to the stock setup.
While on DSMTuners, I found a vendor who made this comment in a post two years ago:
You might want to keep the hose connected to the valve cover & intake. W/ it connected the suction from the turbo sucks the extra crank case pressure out of the valvecover... ever notice your dipstick popping out? Try reconnecting the hose & watch how it misteriously doen't pop out anymore.
I'm not sure how the valve cover breather can effect crankcase pressure (pressure offsets pressure???) but I'm happy to report that my problem only occurred once and I have tortured it to see if the dipstick thing could be induced again and the answer is no. I have returned my car to the stock setup.
Last edited by Smogrunner; Apr 17, 2004 at 10:28 PM.
Apr 17, 2004, 10:06 PM
#3
I just checked out the mod, Since your using a fuel filter as a "oil catch" as it builds up oil, it can get more restrictive and not breathe correctly.. The aftermarket catch cans are not recirculating, they will have to be drained eventually. If you were to remove the filter element from the fuel filter, it can be a resevoir for the oil to get trapped inside and not be a restriction. when there's POSITIVE intake pressure, (Engine under boost) the crankcase pressure gets forced out the breather, so if its too restrictive or plugged, it can pop the weakest point (the dipstick)
just an additional comment from my original PM that i sent to you since I didn't see your mod until I saw that thread.
just an additional comment from my original PM that i sent to you since I didn't see your mod until I saw that thread.
Apr 17, 2004, 10:07 PM
#4
Jack, I hope you don't mind me posting your PM you just sent me. Thank you very much for taking the time to explain things:
"Good news is its nothing.. It probably was a combination of blowby and slightly overfilled oil (possibly a little foaming) Our PCV systems only handle a certain amount of air.. when you increase blowby slightly (higher cylinder pressure), and it can't vent it to the PCV system or the catch tank you get enough positive pressure that can pop the dipstick out, since the level was a little high, the oil got forced through the tube. Odds are the slightly high level covered base of the dipstick tube partially and allowed the oil to travel up the tube and force the dipstick out since liquid doesnt compress like air does, there's only one place for the tube to go.. Out..(sort of like a barometer and air pressure, you raise the pressure and force the liquid up into the tube)
ultimately you vented the bit of extra oil and it dropped just enough to no longer cover the tube.
This would generally not be an issue on the road since the dipstick tube is on the front of the engine so the oil sloshes back, it may happen on steep downward grades, heavy braking and/or left hand turns on a track if it were to happen again.
Feel fortunate, Pontiac and Olds V8's have this happen all the time, most of the time it has to do with the dipstick length being too long and being popped out by the crank counterweights.. Thats not an issue for us.
Again, since it hasn't happened since, I wouldn't worry too much about it, but even if it did happen on occasion with race gas, its nothing to be overly concerned about unless your getting foaming (the crank counterweights beat into a high oil level and aerates the engine oil, that could be bad, but as long as your levels are in check, your ok) This can potentially happen to ANY engine that has a wet sump crankcase (and it does on occasion)
As long as the PCV System (back of the valve on the valvecover, rear of engine, about 2" from the left side from the timing chain cover, the catch can only traps extra oil as it dribbles out of the valvecover otherwise its an air vent, air intake) is functioning correctly, the engine blowby and gasoline vapor etc, are being brought into the engine through the PCV valve. If the valve is plugged, or nonfunctional or just vented it will build up enough positive pressure to regularly pop the dipstic out.. Since you said your catch can is home built, verify that your PCV valve is still there.
Jack"
By the way, my stage 1+ made 311whp on Shiv's dyno on race gas and 278whp on 91.
"Good news is its nothing.. It probably was a combination of blowby and slightly overfilled oil (possibly a little foaming) Our PCV systems only handle a certain amount of air.. when you increase blowby slightly (higher cylinder pressure), and it can't vent it to the PCV system or the catch tank you get enough positive pressure that can pop the dipstick out, since the level was a little high, the oil got forced through the tube. Odds are the slightly high level covered base of the dipstick tube partially and allowed the oil to travel up the tube and force the dipstick out since liquid doesnt compress like air does, there's only one place for the tube to go.. Out..(sort of like a barometer and air pressure, you raise the pressure and force the liquid up into the tube)
ultimately you vented the bit of extra oil and it dropped just enough to no longer cover the tube.
This would generally not be an issue on the road since the dipstick tube is on the front of the engine so the oil sloshes back, it may happen on steep downward grades, heavy braking and/or left hand turns on a track if it were to happen again.
Feel fortunate, Pontiac and Olds V8's have this happen all the time, most of the time it has to do with the dipstick length being too long and being popped out by the crank counterweights.. Thats not an issue for us.
Again, since it hasn't happened since, I wouldn't worry too much about it, but even if it did happen on occasion with race gas, its nothing to be overly concerned about unless your getting foaming (the crank counterweights beat into a high oil level and aerates the engine oil, that could be bad, but as long as your levels are in check, your ok) This can potentially happen to ANY engine that has a wet sump crankcase (and it does on occasion)
As long as the PCV System (back of the valve on the valvecover, rear of engine, about 2" from the left side from the timing chain cover, the catch can only traps extra oil as it dribbles out of the valvecover otherwise its an air vent, air intake) is functioning correctly, the engine blowby and gasoline vapor etc, are being brought into the engine through the PCV valve. If the valve is plugged, or nonfunctional or just vented it will build up enough positive pressure to regularly pop the dipstic out.. Since you said your catch can is home built, verify that your PCV valve is still there.
Jack"
By the way, my stage 1+ made 311whp on Shiv's dyno on race gas and 278whp on 91.
Apr 17, 2004, 10:18 PM
#6
By the way, I just went outside and blew on the fuel filter that was on the car when my dipstick popped and it was very difficult to push air through. Did the same to an unused fuel filter and it was very easy to push air through. However, that explains the restriction, what about the comment from the DSM guy who claims that the suction from the turbo sucks the extra crankcase pressure from the valve cover? Could this actually counterbalance crankcase pressure?
Trending Topics
Apr 17, 2004, 10:32 PM
#8
yes... though he's a bit confused on how it works..
Basically at part throttle, the car runs under vacuum.. so the PCV system draws air out of the crankcase through the PCV valve, and into the intake manifold.. Under BOOST, the valve stays closed and the air is vented into the breather (happens on normally aspirated cars at WOT too) since it relies on the vacuum.. That is why the vent tube in the MAF pipe is a bad thing, the oil gets into the intake tract alot easier. but its an emissions thing.
at WOT the engine blowby creates pressure there's also pressure created from the crank moving,etc... Normally under part throttle cruising its drawn into the intake manifold..
To make a long story short, the combination of additional pressure from blowby, and that boost closes the PCV valve alot sooner than a normally aspirated motor, that air has to go somewhere.. and it goes out the path of least restriction, since you used that fuel filter, it got saturated with oil and couldn't move the air needed. the oil coming out of the dipstick tube is fairly rare when the dipstick comes loose, but slightly high levels, the fact that the car is standing still so the oil isn't sloshing to the rear, etc.. It just makes a mess..
Basically at part throttle, the car runs under vacuum.. so the PCV system draws air out of the crankcase through the PCV valve, and into the intake manifold.. Under BOOST, the valve stays closed and the air is vented into the breather (happens on normally aspirated cars at WOT too) since it relies on the vacuum.. That is why the vent tube in the MAF pipe is a bad thing, the oil gets into the intake tract alot easier. but its an emissions thing.
at WOT the engine blowby creates pressure there's also pressure created from the crank moving,etc... Normally under part throttle cruising its drawn into the intake manifold..
To make a long story short, the combination of additional pressure from blowby, and that boost closes the PCV valve alot sooner than a normally aspirated motor, that air has to go somewhere.. and it goes out the path of least restriction, since you used that fuel filter, it got saturated with oil and couldn't move the air needed. the oil coming out of the dipstick tube is fairly rare when the dipstick comes loose, but slightly high levels, the fact that the car is standing still so the oil isn't sloshing to the rear, etc.. It just makes a mess..
Apr 17, 2004, 10:48 PM
#11
I agree with Malibujack. Best to use a catch can setup that does not impede air flow like an inline filter does. Because of the confines of the engine compartment I put together a cheap but effective can. Not pretty but works. The bottle I used is see through and unlike most who route the line back into the MAF hose pre-turbo, I have it venting to atmosphere. The pic below is what the bottle caught after a day at Willow Springs.
More on the not so pretty catch can....
https://www.evolutionm.net/forums/sh...ight=catch+can
More on the not so pretty catch can....
https://www.evolutionm.net/forums/sh...ight=catch+can
Apr 17, 2004, 11:06 PM
#12
yeah, you can use any unfiltered moisture trap.. basically any bottle with two fittings on it, one fitting goes to an air filter, the other fitting goes to the breather tube on the manifold..
the crankcase and valvecover are an integral system.. the pressure finds its way into the top of the head from the cranks through the oil galleys and drainback holes.. so the pressure is "Equal" between the crankcase and the head/valvecover..
If you were to plug the PCV valve, and the breather, your valvecover or oil pan gasket would leak, or all the pressure would find its way out of the dipstick tube..
Since the PCV valve is one way (under vacuum it operates since most of a cars life is spent under vacuum) it will normally draw the excess pressure into the intake manifold, and fresh air will be drawn into the crankcase (if needed since most of the air, mixed with gasoline, enters by cylinder blowby) through the breather.
But at WOT on any car, and under boost on a turbo car, the pressure continues to build, but its no longer being drawn into the intake manifold.. Therefore the air/vapor/oil goes out the breather tube, normally that tube goes into the MAF pipe nipple and burned by the engine.. but its so early in the intake system that it has to pass through everything, the intercooler, pipes, turbo etc..
Ok.. lets just say your drinking out of a mcdonalds cup with a straw.. you suck the soda into your mouth.. the cup is the crankcase, the soda is the air/vapor, your mouth is the PCV valve and when you swallow, thats the intake manifold.. Now lets say that when your drinking, a little soda is always being poured into the cup, when your drinking and swallowing, the soda gets swallowed.. but if you stop, and the cup is still being filled, it will eventually overflow and pour out.. that overflow is the top of the cup.
Make more sense?
the crankcase and valvecover are an integral system.. the pressure finds its way into the top of the head from the cranks through the oil galleys and drainback holes.. so the pressure is "Equal" between the crankcase and the head/valvecover..
If you were to plug the PCV valve, and the breather, your valvecover or oil pan gasket would leak, or all the pressure would find its way out of the dipstick tube..
Since the PCV valve is one way (under vacuum it operates since most of a cars life is spent under vacuum) it will normally draw the excess pressure into the intake manifold, and fresh air will be drawn into the crankcase (if needed since most of the air, mixed with gasoline, enters by cylinder blowby) through the breather.
But at WOT on any car, and under boost on a turbo car, the pressure continues to build, but its no longer being drawn into the intake manifold.. Therefore the air/vapor/oil goes out the breather tube, normally that tube goes into the MAF pipe nipple and burned by the engine.. but its so early in the intake system that it has to pass through everything, the intercooler, pipes, turbo etc..
Ok.. lets just say your drinking out of a mcdonalds cup with a straw.. you suck the soda into your mouth.. the cup is the crankcase, the soda is the air/vapor, your mouth is the PCV valve and when you swallow, thats the intake manifold.. Now lets say that when your drinking, a little soda is always being poured into the cup, when your drinking and swallowing, the soda gets swallowed.. but if you stop, and the cup is still being filled, it will eventually overflow and pour out.. that overflow is the top of the cup.
Make more sense?
Apr 17, 2004, 11:16 PM
#14
Thanks Jack. I could have done without the McDonalds comparison though. Some of the Vishnu crowd gets in trouble with McDonalds jokes because of Evo8Power. 
But I do understand your point and once again thanks for the patience and time. I don't have anymore questions. I am crashing out tonight with a lot less trepidation regarding the health of my evo motor than the last two nights.
But I do understand your point and once again thanks for the patience and time. I don't have anymore questions. I am crashing out tonight with a lot less trepidation regarding the health of my evo motor than the last two nights.
