PCV drain back instead of catch can
I want to drain the PCV line back to the pan instead of using a catch can. Can I put a Tee in the turbo drain back hose for that purpose?
Boyd, here in SoCal has done it with a check valve in the drain back line.
The 1/2" line that I have now from the valve to the air box, drops down below both the air box and the PCV at the valve cover but it then goes back up to the air box. That is, there's a low spot in the line.
Im wondering about putting a Tee at that low spot in the line because from there it is still more downhill to a spot on the turbo drain back hose where I could put a second Tee to enable any oil in the PCV line to drain back to the sump.
Your comments would be appreciated, for instance, what about blow by from the sump, when the PCV valve is closed? Where does the pressure go in a stock engine when the PCV is closed by boost? If I install a drain back hose that's where the pressure would be relieved up to the air box
Re: PCV drain back instead of catch can
Some of the later cars actually had a tee in the oil drain off of the turbo to drain the stuff that gets in the bottom of the air box.
Re: PCV drain back instead of catch can
Maybe I am alone in this regard, but i would recommend against draining the pcv drains back to the pan.
If you ever look at what those pcv condensation drains look like, you wouldn't want to consider using to lubricate your engine.
Think about what the pcv is removing, and what evaporates out of the oil when the engine gets up to oerating temp.
Some of it is moisture, some of it is fuel, some of it is oil, some of it is non-condensible. The non-condensable just gets removed as vapor, but those others eventually do condense. Moisture can boil out of the oil to some degree if the oil gets hot enough, fuel the same way. But those can recondense in the catch can as that cools away from the heat.
It is best to drain that off seperately and discard rather than put back into your crankcase that just removed it.
Re: PCV drain back instead of catch can
I agree with that.
John, are you doing this to look CA legal?
Re: PCV drain back instead of catch can
Thanks Wayne; good point.
Brian, no, as stock just left whatever vapor that wasn't sucked back into the intake to condense and drip out the air box weephole and then run all over the top of the transaxle
I guess I want to do it because I've hassled with catch cans before and they're a PITA to fabricate mount and service. And, they have to work with a functioning PCV too. And, I don't want a messy transaxle
What I'm really asking here, is whether a check valve, or a second PCV valve, is necessary in this proposed drain back line. What's the theory? Boost or manifold pressure closes the PCV valve under boost and manifold pressure or vacuum pulls the check valve open when not under boost so blowby fumes can be ingested by the intake under cruising vacuum. Well WTF is that? Where does the blow by go when under boost? When the PCV valve is closed - because of boost? Under boost - that's when the blowby relief is needed most because that's when the engine is making the most blow by, right?
Re: PCV drain back instead of catch can
The blowby relief under boost goes to the airbox. It goes there all the time but there's just the T in the line with the PCV so when not in boost the PCV sucks air from the airbox and the crank case.
Re: PCV drain back instead of catch can
Had to edit - cell phone is too difficult . .
Thank you, Jay. In looking at the parts now I see that the Tee which holds the PCV valve is always open to the air box. Thus, blow by, under all conditions is drawn to the air box. Then, under boost, the PCV closes and blocks the release of boost pressure from the intake manifold but under vacuum it opens and thereby allows the sleight continuous vacuum of the air box AND the greater vacuum from the intake manifold to both draw from the valve cover.
Re: PCV drain back instead of catch can
Turbo cars and pcv systems are just a PITA. I bought a moroso catch can and just run the hose from the v/c straight to that and eliminated the pcv valve.
Re: PCV drain back instead of catch can
Quote:
Originally Posted by
johnl
What I'm really asking here, is whether a check valve, or a second PCV valve, is necessary in this proposed drain back line. What's the theory? Boost or manifold pressure closes the PCV valve under boost and manifold pressure or vacuum pulls the check valve open when not under boost so blowby fumes can be ingested by the intake under cruising vacuum. Well WTF is that? Where does the blow by go when under boost? When the PCV valve is closed - because of boost? Under boost - that's when the blowby relief is needed most because that's when the engine is making the most blow by, right?
What you have written here is exactly why I'm running two PCV valves. My "main" PCV valve (the all-metal Supra valve) opens under vacuum, drawing the fumes in. It's installed in the usual spot - between the valve cover and the intake manifold. My second valve is installed facing the same direction with regards to the valve cover, but the other end is open to atmosphere - a hose runs down the side of the engine bay and slightly under the car. That serves as my in-boost relief while the main PCV is forced closed under boost. Not the cleanest way to do it, but theoretically sound I think:
In vacuum: draws fumes through the first valve and into the intake, second valve sucked shut due to vacuum.
In boost: first valve is closed by boost, fumes allowed to escape through second valve.
Keep in mind that this is on a 2.4, so there are two nipples on the valve cover. I know the 8V TBI cars had 2, but I can't remember if the turbos did.
Re: PCV drain back instead of catch can
Quote:
Originally Posted by
jonnymopar
What you have written here is exactly why I'm running two PCV valves. My "main" PCV valve (the all-metal Supra valve) opens under vacuum, drawing the fumes in. It's installed in the usual spot - between the valve cover and the intake manifold. My second valve is installed facing the same direction with regards to the valve cover, but the other end is open to atmosphere - a hose runs down the side of the engine bay and slightly under the car. That serves as my in-boost relief while the main PCV is forced closed under boost. Not the cleanest way to do it, but theoretically sound I think:
In vacuum: draws fumes through the first valve and into the intake, second valve sucked shut due to vacuum.
In boost: first valve is closed by boost, fumes allowed to escape through second valve.
Keep in mind that this is on a 2.4, so there are two nipples on the valve cover. I know the 8V TBI cars had 2, but I can't remember if the turbos did.
The second should vent into the airbox/air intake tube, so that the slight vacuum created at the turbo inlet under boost will pull the pressure out of the crankcase. This is how the factory did it. The turbo valve covers only have one nipple for both PCV valve and the vent.
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Re: PCV drain back instead of catch can
I put a PCV valve in the drain oriented so that it checks any boost/bow by that may come up the turbo drain back line from the crankcase. That way, during cruise, any oil from the valve cover can drain back to the sump by way of the PCV line's connection to the turbo drain back line but any reverse flowing air from crankcase boost/blowby won't interfere with oil draining out of the turbo.
