Can an aftermarket PCV valve cause crankcase pressure issues if plunger is too heavy?

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499
Edit: I don't know a whole lot about all the fine details involved with PCV systems, so it's just a guess on my part that the plunger weight has anything to do with it. For all I know, it could be any other aspect, or maybe my oil loss issue isn't PCV related at all.

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I was doing some maintenance on my van yesterday and decided while I was in the back of the engine, to replace the grommet and PCV valve. I had replaced the PCV valve a few months ago with an aftermarket one from the auto parts store, as it was quick and cheap. This time, I ordered an OEM valve.

When I pulled the aftermarket one out, I noticed it has a WAY heavier plunger inside than the OEM one. Like in the order of maybe 2-3 times as heavy. The OEM one rattles when shaken but can't feel the plunger much, where as the aftermarket one feels like a shake weight and hits much harder. Since the PCV valve points straight down, that weight is holding it closed against higher amounts of pressure. How much? I don't know.

Is this a sensitive aspect of PCV valves? Looking at the internals of the aftermarket valve itself, it doesn't appear much of anything has been going through it. The bottom below the plunger on the crankcase end had a little bit of residue, but the exit going to the air intake didn't appear to have anything.

I purchased this vehicle last summer used for pretty cheap. It didn't leak much oil, except for maybe a drop or two once a week, if that. When I did the first oil change, I replaced the PCV valve with the aftermarket one. I started getting a lot more oil dripping on the ground and weeping from the valve covers shortly after this and attributed it to using full synthetic oil on an old engine. It was PUP FS oil which I believe is actually pretty thin for the viscosity grade of 5w-30.

Do any of you with experience with this matter think having a much heavier PCV plunger mounted vertically would create enough extra crankcase pressure to cause old seals to leak more than they would otherwise? Yes, I know the standard "fix your dang seals dummy" response, but that's expensive on these vans, especially when not needing to do other work while it is all taken apart. It can come at a later date.

Or is the weight of the plunger not relevant and it could just be other aspects that may have caused issues?
 
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466
Location
Kentucky
The spring actually holds it open not closed. So technically, if everything else is the same a stronger spring will let more air through pcv valve. A bit more is better than less in most cases. My opinion.
 

MrPlow

Thread starter
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499
The spring actually holds it open not closed. So technically, if everything else is the same a stronger spring will let more air through pcv valve. A bit more is better than less in most cases. My opinion.
Ah, so the heavier plunger might have actually kept it open at higher revs and not closed like I incorrectly thought?
 
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25,956
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MA, Mittelfranken.de
There are consequences with either more or less flow. A PCV valve or orifice is a well controlled vacuum nothing more or less. Too much flow can cause lean mixture, rough idle, high fuel trims (less fuel economy), etc. Too little flow can cause varnish, deposits and sludge, pick your poison.
OE is specifically designed to work with that engine unlike some aftermarket that just may do, for the couple of bucks its just not worth it.
 

MrPlow

Thread starter
Messages
499
There are consequences with either more or less flow. A PCV valve or orifice is a well controlled vacuum nothing more or less. Too much flow can cause lean mixture, rough idle, high fuel trims (less fuel economy), etc. Too little flow can cause varnish, deposits and sludge, pick your poison.
OE is specifically designed to work with that engine unlike some aftermarket that just may do, for the couple of bucks its just not worth it.
In your opinion, is it possible for a poorly designed or improperly designed PCV valve to allow excessive crankcase pressure at some point in the RPM range?

When I do the rear valve cover gasket on the v6 against the firewall, I might also put in a redesigned valve cover with improved PCV venting, and a screw-in PCV valve. It's well known that the original system is very poorly designed and can cause all sorts of issues if not in perfect working order.
 
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35,689
Location
NY
There are consequences with either more or less flow. A PCV valve or orifice is a well controlled vacuum nothing more or less. Too much flow can cause lean mixture, rough idle, high fuel trims (less fuel economy), etc. Too little flow can cause varnish, deposits and sludge, pick your poison.
OE is specifically designed to work with that engine unlike some aftermarket that just may do, for the couple of bucks its just not worth it.
+1 Too much flow can cause in increase in oil use too. Ask me how I know. ;) Bottom line, pay up for an OE PCV valve.
 
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466
Location
Kentucky
Ah, so the heavier plunger might have actually kept it open at higher revs and not closed like I incorrectly thought?
The heavier spring may be keeping the pcv valve further open during high vacuum conditions. Then again the internal geometry of the pcv might be different than the oe version so it’s hard to determine based on feel. If you believe it may be causing issues, a new OE valve would provide peace of mind.

make sure breather side is hooked up right and not clogged top of course
 
Messages
25,956
Location
MA, Mittelfranken.de
In your opinion, is it possible for a poorly designed or improperly designed PCV valve to allow excessive crankcase pressure at some point in the RPM range?

When I do the rear valve cover gasket on the v6 against the firewall, I might also put in a redesigned valve cover with improved PCV venting, and a screw-in PCV valve. It's well known that the original system is very poorly designed and can cause all sorts of issues if not in perfect working order.

Absolutely, if there is a proven upgrade then by all means use it.
 
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3,243
Location
USA
If the crankcase ever goes to positive pressure, it will flow out backwards through what is normally the inlet hose to the air pipe before the throttle plate. There is no valve in that hose.

So a couple ounces different in the PCV valve really isn't a factor in what happens with a worn engine at high rpm making lots of blow-by.
 
Messages
25,956
Location
MA, Mittelfranken.de
Positive pressure can blow seals out especially rear main and front crank seals. I have to wonder how many rear mains were blown out for this reason (wrong PCV fitted) when there is no wear on the sealing surface of the crank and no apparent damage to the seal eg cuts, hardening or splits.
I have no idea just thinking out loud.
 

MrPlow

Thread starter
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499
So, I did a little bit of literal poking around in both the PCV valves on my older Toyota vehicles. Toyota used a gravity system in these that holds the PCV valve effectively shut with the plunger. I took two valves and held them upright and blew air through them. There is a certain amount of "stiction" or initial pressure needed to open them up at all. Because of imperfections in the manufacturing (or by design) there is a very very tiny bit of bleed-by, but for the most part, it seems it takes a certain threshold of pressure to open them up at all.

Now, on the top of the valves is a small spring, which seems to help regulate the pressure at higher RPMs, but the spring does not engage until the heavy plunger inside is up a good ways. Just as a rough guess I would say it takes 1 or more PSI delta to get any meaningful crankcase vapor flow going.

The aftermarket one in my van that started leaking oil when the PCV was installed, had a much heavier plunger inside and seems to require considerably more pressure for the initial opening/lifting of the metal plunger. The OEM one takes an almost imperceptible amount of pressure to lift the plunger, while the aftermarket one was very noticeable.

Seeing as how one engine has over 200,000 miles and the other over 300,000 miles, I can say there is a good chance of blow by at the pistons. I wonder if the added pressure from this may have been a reason why the valve covers leaked immediately after using the aftermarket PCV valve?
 

wdn

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1,641
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NH
This a kind of a wacky place were people will stash 200 qts of oil they don’t need or pay $15 for an oil filter that filters 1% better than another one but still change it every 5,000 miles. But will cheap out on a PCV valve a vital engine part and one that can last 100,000 miles if you stick with OEM. The consequences of a poorly designed, underperforming or failed PCV can be grisly.
 
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