Honda Odyssey Forum banner
Cancel
Create thread New Garage Forums

What's a PCV?

Jump to Latest
1 - 14 of 14 Posts
A

Atlanta Odyssey

· Registered
Joined
·
159 Posts
Discussion starter · #1 ·
Okay, I actually know what PCV valve is-- at least I used to... It is a positive crankcase ventilation valve. They used to be hooked to a vacuum line to evacuate blow-by and general undesirable gasses floating around in a crankcase. They take the exhaust gas and let a hose suck it back into the intake manifold, where the junk gets burned in the combustion chamber. And they are one way valves where things cannot flow back into the crankcase through them...

Okay, simple enough. Only today I learned that the PCV valve on my Odyssey has no vacuum line attached? Really? How exactly does that work?

I was wanting to see if the slight oil leak I have might be caused by a PCV issue. So little of a leak that mostly it seems to be that I smell oil and see a tiny bit of oil smoke around the engine when I turn it off, but there is no oil dripping, or worst case, just a tiny drip.

Interestingly, the oil smoke seems to be coming up from the front side of the engine, down below the PCV location.

I looked up where to find the PCV (down by the oil dipstick). I unbolted the old one-- this once I realized the reason I couldn't find it based on the vacuum hose because it apparently HAS no hose, and tried to remove it. Well, it was a bit tight, or otherwise stuck. A slight tap made the thing disappear, almost like a rather mean magic trick...

I'm sort of stumped-- it slipped forward and went "plink" and I cannot find it anywhere. I wanted to see the condition of the thing before I replaced it. It is not under the car. It is not inside the fan housing. My best guess is it went under the radiator or else under the engine (etc.) in a supporting member of the frame.

So all I could do was replace the part. I got an OEM PVC valve and inspected it-- Okay so there is no hose, and apparently there is no "one way" action, as I could pass air through it both directions.

I actually bought it at a local parts store, but the box contained what appears to be an OEM Honda PCV in a sealed Honda plastic package. Could it be a defect? Sure, but that seems unlikely.

It seems much more likely that I'm getting old and the world is changing too fast, but I'd sure like a little more information about why a PCV apparently no longer burns off the offending gasses or is actually a positive valve at all.

Does anybody have some information to shed some light? I cannot check the leak right now because I'm still fighting with a different issue, but once we're running again, I'm awfully anxious to see if this improves things a bit...
 
Discussion starter · #2 ·
As I review other posts, I'm reading to pinch the hose coming from the PCV to check it and other references to a line that runs to the PCV. I have no such line, nor do I see any dangling lines anywhere. Where should this be?

I took this van to a local shop for this oil leak already-- they said it was a leak from the power steering O-ring issue and fixed it for me, but the problem never vanished. Has somebody got a photo or diagram that shows where this line should be, if indeed the world has not fundamentally changed, and PCV's actually DO still vent to a vacuum line???
 
#3 ·
The PCV valve is not by the oil dipstick, See the attached for location of the PCV and testing...
 

Attachments

Discussion starter · #4 ·
Thanks, that actually appears to cover only the 1999-2004 Models. Apparently I forgot to post the year of the van, so I will see of I can edit that. This is a 2006. I cannot find a diagram for an '06, but I will try and attach one that claims to be for a 2007, which seems to match what I have, and 2006 & 2007 are both Gen 3 years.

I asked for a PCV, and they gave me box that said it was a PCV, and the inner package was apparently a Honda OEM PCV (in a plastic pouch with Honda logos printed on it) that bolts, nearly flush, to the side of the motor (I guess that's the valve cover there) next to the bright orange dip stick. I'm 99% certain I also read "PCV" in the packaging from Honda, but I think that already went in the trash.

I didn't show them the part, or describe the part, I just said I needed "a PCV for a 2006 Odyssey" and they gave me what I expected, which matched the diagram and which fits perfectly, both in the way it inserts, and in bolting up... but there is no nipple where a hose would generally attach, nor do I have any sign of a hose on the car.

It also looks just like the part I was removing, which (as I mentioned) unfortunately slipped and went into never-never land. There was absolutely no nipple on the part I removed.

The PCV is apparently item 9, and the dip stick is item 8 in the attachment.

The diagram is from a post elsewhere on the forum:

http://www.odyclub.com/forums/14-pe.../forums/14-periodic-maintenance/93366-2007-ex-l-odyssey-pcv-valve-location.html

If you read through the above thread, you will reach the following suggestion:

"To check its operation, you will need a stethoscope. At idle, listen to the PCV valve as you lightly pinch the PCV hose (which is the hose that is above the PCV valve and runs to the intake manifold) with your fingers or pliers several times. Each time the hose is pinched, the valve should click."

I agree with the suggestion, and I'm well familiar with that trick. There appears to be no such hose to pinch. I'm nearly 50 years old. I've been working on cars since my teens. I've worked on a lot of cars, and I've changed plenty of PCV's. I used to change my own engines and transmissions because I thought it was fun-- no idea what that was about, but I was 30 years younger then... This thing has nothing obvious in common with any PCV that I have ever messed with, but I have mostly worked on older cars, and from the last post, PCV's apparently are the same as recently as 2004, even on these Hondas, so I don't know what is going on here...

I know I sound like an idiot, and if someone had told me they had a PCV with no hose, I'd immediately assume they had the wrong part, or they were not seeing where a hose had gone missing, or they were otherwise confused... and there is a slight chance a very small hose could fit INSIDE the part as there is a cylinder that could receive a hose, (the hose becoming the male part and the PCV being female) but there would be nothing to retain the hose-- as there typically is with a conventional PCV-- like a little ring where the nipple is broader that keeps the hose from sliding off.

So I'm pretty much stumped...
 
#7 ·
Don't bother testing it, once the car reaches 90K-110K, most PCV valves are gone.
Cheap preventive maintenance PN 17130-RCA-A02, $17.

The PCV hose sits above it (I took the photo from my other DIY serp belt DIY but labeled the PCV hose)...
 
Discussion starter · #8 ·
So can anyone confirm there is not a missing hose here and this is indeed a PCV which has no associated vacuum line?

I still cannot grasp this being proper, even if only for emissions reasons, (as it apparently works without the line) to just vent any associated gasses from the engine to the atmosphere and not burn them.

The fact that air seemed to pass through the valve either way, right out of the package makes this all seem even more suspect, but I have no other valve to compare with.

From what I can see, this setup acts just like the old-fashioned vent caps that were used to be on many old cars. I've had them on countless chevy v-8's, but that just cannot be...

Given this came in sealed pouch, I doubt I can compare to another one in the store without spending another $25 or so either...
 
Discussion starter · #9 ·
Thanks. I'm not worried about testing the old one. I want to know why the new one seems to have a two-way valve. I guess maybe one has to hold it at a particular angle or it doesn't seal in the opposite direction. That would make sense... The old fashioned valves' angles were pretty obvious in the top of a chevy valve cover, for example. This valve sits pretty close to horizontal, but it does lean slightly-- I know this because once it came loose, the old valve fell out on it's own-- it slopes downhill towards the front of the car. That probably means I was testing it upside down, without realizing it. It does seem like at the angle where it resides, a steep uphill, or strong acceleration would just open the valve no matter what... It is a little disorienting where it sits...

That is very interesting that the hose is on the other side of the valve cover. So it isn't, apparently, venting to the atmosphere, but the valve isn't a positive valve-- it is negative. (The SYSTEM is positive-flow, but the valve would have to open to let air IN.)

I was hoping a stuck PCV was causing my sight oil leak, as others have suggested. If this is a one-way, in-only valve, it makes it seem less likely that a failure would cause an engine oil leak as the engine wouldn't be getting over pressurized. It also seems like these would be less likely to clog, because clean air would mostly be passing IN through the valve, while the oil residue would pass straight through the hose to the intake to burn.

My main point is that I would think a stuck valve in this case wouldn't cause oil to blow out somewhere, but would instead cause the engine to suck more blow-by gas with low pressure in the crank case with this design... Has anybody found this not to be true?

I guess if it sticks open it could cause such a leak...
 
Discussion starter · #11 ·
Others here may have more information than I, but basically, if they get clogged up, PCV's stop venting properly, and can cause excess oil consumption, oil leaks, potentially even failed oil seals (from the excess pressure in the crankcase), and various other strange behavior from the engine, including reduced fuel economy and going as far as making the engine virtually inoperable.

Typically, you end up with pressure inside the crank case that is too high (though that may or may not apply here with the unusual design on the Gen 3 Odysseys-- the pressure might be too low in this case, but that's just a guess).

Usually, the gasses get sucked outside of the engine through a vacuum tube on the end of the the PCV from outside of the engine. I'm not pulling mine back out right now to confirm, but as I think about it, that may be the case here as well, only with the exit starting INSIDE the cover through a channel inside the valve cover casting... the high end of the PCV is inside of the engine may actually be the PCV exit-- continuing through the valve cover, and into the hose heading to the intake manifold... I think there were openings on the side of the PCV as well so the gasses could pull in from there.

If I saw that correctly, there was also an opening outside of the engine, where the valve protrudes (by the bolt). Maybe someone with an extra PCV handy for a Gen 3 can conform this?

Surely some Honda specialist can clarify this for us, but my best guess is the Gen 3 PCV may possibly blend fresh air from outside the engine with internal gasses based on internal engine pressure... Usually they just suck gasses from inside the crank case, valve covers, etc.

Every other PCV I've used for the last 30 years or so had just one opening on each end and was pretty straightforward. Since this PCV line exits the valve cover from the top, but the PCV is in the bottom side of the valve cover, there's no clear picture of what is happening inside in the raised channel that seems to be involved with this setup. (I'd like to see the inside of that valve cover!)

When the PCV valves don't work as they should, exhaust "blow-by" gasses from combustion end up staying where they should not be inside the engine, building pressure and such, so it is somewhat of a roll of the dice as to what happens next.

Best to change the valve before this happens. Some people are happy just to clean them out with engine degreaser or brake cleaner. That's probably okay too, but replacements are pretty cheap and should be the longest lasting solution, as cleaning most likely will not make it work as well as when brand new.

I haven't opened one, but these would seem to be basically "check valves" for exhaust gasses in the crankcase. Over time, you suck enough exhaust and oil vapor past something that feels like a ball bearing rattling around, and the thing gets gummed up. Finally it gets to where it sticks and the valve no longer operates. This is why the default check of a loose PCV is to shake it and listen for a rattle. This is also the "click" people listen for with a stethoscope when the hose is pinched and the engine is on. Pinch the hose and the valve falls down. Release the hose and the vacuum sucks it back open.

The newer valves are not so noisy and easy to check as the big valve in an old Chevy V-8. They are a lot smaller, so they're probably harder to clean effectively, but any way you slice it, big or small, the chances are you won't wash 100,000 miles of oil and exhaust residue completely out of a 5 or 10 year old valve very easily...
 
1 - 14 of 14 Posts
About this Discussion
13 Replies
6 Participants
Last post:
odiuser
Honda Odyssey Forum
posts
1.1M
members
432K
Since
2000
Odyclub community is the #1 forum to discuss all things Honda Odyssey: minivans, safety, service maintenance, mods, and more.
Full Forum Listing
Explore Our Forums
2005 - 2010 Odyssey 2011 - 2017 Odyssey 1999 - 2004 Odyssey 2018+ Odyssey Problems and Concerns