737 Jock

Combustion gases "blow-by" the piston rings during the compression stroke, and enter the crankcase. They dilute the oil and promote corrosion and sludge.

Positive Crankcase Ventilation serves to cycle clean air through the crankcase, evacuating the combustion gases, by using intake manifold vacuum as a motive force.

On the RDX, the PCV valve vents from the engine block directly to the intake manifold runners, downstream of the entire intake system (the charge air cooler and throttle body).



At idle and low RPMs, vacuum in the IM draws the spring loaded PCV valve open and creates negative pressure in the crankcase. Clean, filtered air from the airbox is tapped off the turbo-charger inlet pipe by a breather hose, and drawn into the crankcase at the valve cover. This clean air sweeps through the crankcase, carrying the blow-by gas and oil-mist out through the PCV valve, where it is fed into the intake ports to be burned. The flow is one way >> breather hose >> crankcase >> PCV valve >> intake port.

However, in turbo-charged cars the motive force of IM vacuum only occurs at low RPM. Under boost the IM is pressurized and pressure in the PCV line closes the PCV valve, stopping ventilation. There is concern in the forced-induction tuner community that PCV valves do not seal well enough. Boost pressure forces past the PCV valve, pressurizing the crankcase and blowing contaminants the wrong way; out the breather hose into the turbo-charger inlet pipe. The gasses and oil-mist then travel through the entire intake system; compressor >> charge air cooler >> throttle body, and the oil-mist condenses into sludge in those components.

Sport compact tuners have installed oil catch cans at both the PCV hose and the breather hose to keep contaminants out of the engine and intake. This is a high quality dual OCC available from Saikou Michi Filtration:



Each OCC is simply fitted in series in the two hoses. For instance, the engine block PCV output flows through the can, then exits into the IM. The OCC condenses oil out of the flow like this:



The collected oil is then drained from the bottom valve.

What could possibly go wrong with this???

A. The breather hose OCC rarely catches anything as it is filtering clean intake air.

B. Sometimes the breather hose OCC is hooked up backwards, restricting flow.

C. Sometimes the breather hose and PCV hose are joined and routed into a single OCC. This stops the motive vacuum flow of cleaning air through the crankcase. (Some air will still exit due to crankcase pumping pressure/temp rise.)

D. The OCC in the PCV line is connected directly to the IM. When boost pressure hits, it backpressures the can and line, forcing contaminants against the PCV valve, gunking it up. The can is subject to continuous negative/positive pressure slams.

E. If either OCC is mounted higher than it's inlet line, residual contaminants will run down into the turbo-charger inlet or PCV valve, when the engine is off.

F. Unbaffled, poor quality OCCs don't catch the oil at all.

G. To avoid using a breather hose OCC, sometimes the breather hose is disconnected and a K&N type filter is fixed to the end. Crankcase pumping pressure forces contaminants up the hose, coating the inside of the filter, restricting it. Additionally, open venting violates emissions rules.

Can high quality OCCs be useful? Yes, but the PCV valve must be relocated in the PCV line to protect the OCC from turbo-boost backpressure. The valve must be on the outlet side of the OCC. (Alternately, a second check valve can be installed at the outlet, but this restricts flow further.) The cans and baffles must be kept clean.

Does the RDX need OCCs??? It's only important on the breather hose if the PCV valve is letting boost air pressurize the crankcase, forcing oil out the breather. I have disconnected my breather and found no evidence of oil.

On the PCV hose however, it will keep oil out of the combustion process. Many tuners view this as a neccessity for power and service life.

Aside from an OCC install, what can you do???

Keep the PCV valve clean and sealing tightly. Change the oil and filter on schedule with HTO-06, 5W-30 synthetic, and test the PCV valve every service. Consider replacing the PCV valve with the spark plug replacement (every sub-item 4).

737 Jock

I don't mean take it out and clean it, just keep the oil fresh. You can test it by pinching the hose at idle.

MakTypeR

Good info, thanks!

mau108

on my NA h22a4 (honda prelude) I found the OCC to collect alot of gunk.

Will take pics when I empty this weekend. I once had it top up with coffee color water :S freaked me out. I don't know if it came from the engine or if it was leaking through the hood and onto the catch can (my catch can is located behind my SRI which is quite close to the edge of the hood....)

Here's the shat that was in my catch can that freaked me out....



That is what happens when you mix oil and moisture in a compressed can

This is what happens in normal warm weather.

dcmodels

Sorry to revive an old thread, but perhaps better than a new one?

So what happens with pinching the hose? I can hear air flow, which stops when the hose is pinched. Is that what I am supposed to notice from the 'test'?

OK, so that tells me that the PCV is properly pulled open at idle vacuum, but how do I know that it is sealing completely during turbo boost (pressure)? is there any simple test?

If there is no more help, I suppose that I will just replace it - thanks for any responses.

737 Jock

Pinch the hose to shut off vacuum and the valve should close with an audible click. If it doesn't click, it may be cracked or gunked up and should be replaced.

If it clicks closed for the idle test, then turbo boost should hold it firmly closed, like pressure sealing a boarding door on an airplane.

If it leaked under boost (or was not working) then it would pressurize the crankcase slightly and vent oil vapor the other way out of the breather hose. You could pull the breather hose off the turbo-charger inlet and look for evidence of oil exiting there. Or seal the hose end in a baggie, cap the turbo inlet nipple and drive it briefly on boost. Then look for oil blowing into the baggie.

dcmodels

^^^ thanks for the fast response --->

I do not understand just which of the many hoses, is the breather hose. When I have time this weekend, I will post a diagram and perhaps you can indicate the part number for the hose - thanks.

OK, I think that I understand now - I have never seen a PCV that is spring loaded. The only ones I have ever seen are installed vertically, and the weight of the internal valve is what closes the valve.

So, in slowly pinching the RDX PCV hose, the valve was slowly closing - hence no click. I am so deaf that I may be unable to hear the click anyway - all I hear is the engine valve clatter, which has always seemed loud to me, but I am accustomed to Hydraulic (non-adjustable) rather than solid (adjustable) lifters.

I will try this again by pinching (quickly) with pliers, after I wrap tape on the plier ends to prevent damaging (cutting) the PCV hose.
---eof

737 Jock

The breather hose is coming off the hump in the driver's rear of the valve cover, to the right of the words "Honda Motor Company Limited".

You have to remove the charge air cooler for access.

Pic is from my thread Remove the Charge Air Cooler and Change Spark Plugs.

dcmodels

Thank you for the picture and the prompt response. I 'borrowed' the RDX driver's ears, as I am completely unable to hear the 'click' of the PCV valve closing, when pinching the hose to the intake. She says that it is more of a soft, *round* pop - love her descriptions. Of course, then I thought that by using a mechanics Stethoscope and pressing the metal end/ tip against the metal of the PCV, I could probably hear the valve closing.

Unfortunately, I mumbled this thought outloud as I was closing the hood, at which point the wife walked away muttering, nothing good I am certain.

My PCV does seem to be operating OK, but at around 40K and 4 years, I have already purchased a replacement, which I will install when I have time, just because.

Well, just because I have started using RedLine 5W30 engine oil, which has a higher amount of ZDDP, which is supposed to be 'bad' for the CAT (catalytic converter). I was concerned about any oil mist going through the engine intake and damaging the CAT, hence my reason to check for a properly operating PCV system. I am using the RL oil because it is better at high temps than most other oils. But I digress, and cannot recommend anyone else use this oil. I will report back on my observations, on another thread, after I have used it for awhile.

dcmodels

Mechanic's Stethoscope to hear the PCV valve operation: as the FSM (factory service manual) states, and as stated above by 737jock, pinching the PCV hose closed, while the engine is idling, will cause the PCV valve to close, making a 'click'.

My old ears cannot hear the click over the engine noise. I used a stethoscope, held against the PCV valve base, as I pinched the hose with padded (duct tape) needle nose pliers.

The stethoscope noise level is quite high - it is necessary to very quickly and completely pinch the hose closed, in order to cause the PCV valve to 'slam' closed, to create a loud enough metallic click that I could hear. The sound is very sharp, short, and very metallic. This worked for me.

SinCity

Subscribed.

bfaucett

I changed my spark plugs this week and found a very thin coating of oil throughout my intake. Assuming its the pcv since my experience has been that a bad turbo puts a lot more oil and causes obvious performance difference. Has anyone done a pcv reroute?

dcmodels

I pulled the intake return hose (rigid tube) and found a bit of oil inside. That is the hose from the turbo blow-off valve back to the intake tube, just before the turbo air-intake. The blow-off valve is located on the driver side front corner of the turbo intercooler, and there is oil inside it too. So, that means that the entire intercooler is coated inside with oil. I did replace the PCV at 40K miles - currently 51K miles. The original PCV valve seemed to be working correctly, and was not stuck or dirty inside.

I too am considering a OCC tanks, but not sure just how to route from the valve cover hose back into the air intake hose - the valve cover vent hose is very short, and the area is very congested.

bfaucett

by reroute I mean vta not a occ

dcmodels

Sorry - VTA ??

bfaucett

vent to atmosphere. My knowledge and experience with pcv has been on diesels which don't use a valve just an open vent off the valve cover. Since the valve on the rdx is vacuum operated by the intake wouldn't the positive pressure from the crank also operate it if intake tube was disconnected and hole plugged?

bfaucett

hole on intake not pcv tube

bfaucett

Bump

WRXtranceformed

Since this got bumped I will ask this question: For those of you running catch cans on stock / mostly stock RDXs, are you getting a lot of blowby caught in them? I ran catch cans on my heavily modified cars in the past as well as my modded, direct injected CTS and they would catch like a 1/4 qt - 1/2 qt in between every oil change. Wondering if it's worth the effort on a stock RDX when I am hearing them going above 200k miles with no issues.

bfaucett

Last time I pulled my intercooler was when I did my spark plugs at 110k. The whole system had thin coat of oil at that point. Idk if it had been cleaned by previous owner but spark plugs had been changed recently

CSmoney28