Drcoffee

For the benefit of those who have not yet concluded that the valve cover is at fault (Salim), let's assume for discussions sake that it is. Has anyone tried to reduce the strength of vacuum coming from the intake plenum by simply adding a restrictor in the 3/8" PCV hose? This would buffer the volume of air being sucked into the intake at the highest vacuum levels such as when you are cruising at highway speeds near 3000rpm, yet allow for moderate volumes of air flow at lower engine speeds. So I'm thinking of a 1/4" reduction in the PCV line.

salimshah

To clarify since not all RX burn oil through intake... my position is ..
1. Verify that you are loosing oil through the intake.
2. Try the updated bank 1 valve cover. anecdotal evidence [many for and 1 against] that the newer valve cover reduced the loss of oil]

Back to your proposal .. physics works in some nonintuitive ways. When you reduce the piping, the pressure differential would increase and the volume/sec (flow) will be less. Time plays an important part as for a short amount of time the net loss of oil will be less.
But as you increase the time there will be a point when net volume of oil lost will be more if you had a wider pipe. The newer valve cover has a larger pipe from the PCV

Finally being human my knowledge is limited and if I look back, I have been wrong many times in the past.

Salim

Drcoffee

So my thought was this. If the volume of air the PCV hose can flow at the intake plenum is X and you reduce it by 30% before the PCV valve, there would necessarily be less vacuum (volume of air flow) pressure at the actual PCV valve and consequently less force exherted on the oil to climb the valve cover to the PCV valve. Whereas the PCV vavle can flow well at idle, it can flow more at higher rpms. Restricting the potential max force of the plenum vacuum would help reduce oil ingestion. If that makes sense.

I am trying to apply bernulis principle where the restriction will produce less pressure but higher velocity but less volume of flow. So the higher negative pressure we call vacuum will be at the restriction, not the PCV valve.

Salim, I was just poking fun. I hope you took it that way.

edit: this is what I had in mind. The OD is 3/8" and ID is 1/4" which should be about the size of the PCV valve. So flow should match the PCV, yet buffer excess vacuum before it.









well someone will have to test the idea, might as well be me. I used a 24" length of 3/8" transmission hose I had laying around which is about 20" longer than the factory hose. Why? The longer the hose, the less impact the sudden increase of vacuum will have when you let off the throttle at highway speeds. The rapid increase of vacuum will be buffered with the greater hose cavity. I inserted the 1/4" restriction about 6" from the intake plenum port. Why? To keep the vacuum force in the hose closest to the intake and less close to the PCV. The hose is routed up and over the strut brace and back down to the PCV valve. Why? So that any oil coming out of the PCV will have a hard time climbing the hose and will drain back into the vlave cover when vacuum is less.

Lexmus

Dr. Coffee, Are you seeing oil consumption even after changing the rear valve cover? If not, how will you evaluate if this is a potential alternate fix for the original valve cover?
I was going to change mine and have purchased the redesigned cover, but have put it off for some other car maintenance and repairs. Additionally using higher viscosity oil has somewhat mitigated my oil consumption, although it still is not ideal. However, I am seriously thinking of trying your idea out before changing the cover.

Drcoffee

I replaced the Gen1 valve cover (push in pcv) with a Gen2 valve cover (screw in pcv) and changed the oil with Mobil 1. Since then, I have put 600 miles on it (2 tanks of gas) and I noticed some loss of oil on the dipstick, about an 1/8" and I added about 1/8" of a quart of oil to bring the level back to the high mark. I also noticed the hose on the pcv nib was wet with oil. Was it a lot? no, but if I can mitigate it, I will try. I'm starting to think the port on the intake is too large for the pcv system. This idea effectively reduces the port size without altering the pcv function. I hope.

FYI, the reducer in the hose is actually an air compressor 1/4" quick connect with male and female threaded ends. You cant see it in the picture, but I used gas resistant teflon tape on the threads to seal it.

I did buy an oil catch can and went to install it, but there is no room anywhere to mount it.

Lexmus,
You are using a higher viscocity oil? I thought people were moving to 5w20 to help the oil drain from the heads better. How much oil are you losing? The Gen1 valve cover baffle is flawed, I would think you would benefit from installing it.

Drcoffee

Salim,
Don't feel bad about being wrong now and then. Toyota really got this wrong and they get paid to get it right.

I'm not sure I follow you on the larger pcv pipe. What are you referring to? If you mean the actual pcv valve, its probably a cobination of housing size and valving inside. The old plastic valve seemed to gum up too quickly and get clogged because the valve housing was too narrow and constantly full of oil. Most likely a combination of issues with the Gen1 design. Regardless of pipe size, the pcv valve orifice size at both ends appears to be the same as the plastic pcv valve.

Lexmus

Oil consumption varies greatly with speed. Around town driving (less than 60 mph) I get no discernible oil loss. I closely watched over 500 miles with no interstate driving and had no change on the dipstick. I then drove 320 miles on the interstate driving 80 mph and burned a quart. I drove back the same distance at 75 mph and burned 1/3 qt.

The oil during this time was 5W-30 PP, and I added 1 qt of Lucas oil stabilizer, which effectively raises the viscosity of the oil to 10W-45. I also know I am burning additional oil in cylinder 2 as that plug was noticeably more fouled than the others when I changed them a few months ago.

Drcoffee

The vacuum generated at higher rpms is greater than at lower rpms which makes sense that you lose more oil at 80mph than 75mph. If I was to go out on a limb, I'd say this confirms its not a piston ring or valve seal issue as the oil loss would be at all rpms. It also makes sense that cyl 2 spark plug is oil coked because the pcv intake port is positioned closest to #2 and the greater volume of pcv gasses will be sucked into that cyl. Whereas the other cyl will be fed by the throttle plate gap.

I am curious if I was to tap a new port in the intake closer to the throttle body where the vacuum would be balanced better with the TB air and have a less dramatic pull on the pcv valve.

salimshah

Let me state this that I have no first hand experience with loss of oil with city driving and Highway driving on less frequented highways of Texas

I suggest that folks should first confirm that they are losing oil from the pcv.

I am of the opinion that the issue has little to do with the amount of vacuum as the suction is not through a tall column .. through a thin straw. Conversely the issue is about the rate of pumping up of the oil in to the valve cover and the rate of drain. The drain in bank 1
is reduced by a factor of cos@ (due to incline). First gen had thinner drain lines and due to lack of maintenance the drain tubes can be further restricted ... note new engine do not exhibit the problem. So if the drain is slower than the fill then the level of oil inside the
valve cover is going to rise. Once it reaches the bottom of the PCV, then it gets sucked in by the vacuum. The new(er) valve cover may raise the position/volume of oil in the valve cover preventing oil from being sucked out.

Salim

Lexmus

So if the PCV valve could be raised out of the first gen cover by an adapter, then the consumption should be greatly reduced or eliminated?

Drcoffee

Lets talk about this a little more. Salim, you propse the drain holes are too small or have been reduced in size by gelled oil. If the same holes that drain the oil from the head simlutaneouly have to allow air up from the crankcase, then the oil is being prevented from draining by force of the vacuum originating from the PCV. I propose a two part solution. Run MMO to thin the oil and perpetually clean the old carbon build up. Second, reduce the volume of air being pulled through the pcv valve as I suggested with a restrictor in the vacuum line.

Lexmus, you may have an idea there, but if the oil up to the pcv and getting sucked into the line, it will also fill the adapter as well. The best solution is to reduce the pull on the oil.

salimshah

There is more than just raising the PCV ... there is a baffle. Think of the the setup as a straw and cup full of milk. If there is a gap .. is there vacuum so strong that it will pull the milk up the straw. Most likely it is the level.

Salim

fastnoypi

if i were to attempt to re-engineer today, i would T the valve covers together. This would allow an equalization of pressure, any oil that would be forced from the rear valve cover in the event of a partially clogged baffle would potentially drain into the front head. The breather on the front valve cover is approximately 1/2" iirc that goes to the airbox.

Drcoffee

That wouldn't work. The pcv draws air from the metered air between the MAF and throttle plate thru the left valve cover, thru the crankcase and out the right vavle cover. I do wonder if it would help to reverse the flow from right to left where the left head is more horizontal and may drain faster.

Your suggestion would essentially bypass the crankcase and allow condensation to blend with the oil.

fastnoypi

No, there would still be breathability. Any condensation that the rear valve cover that contributes to the front still has the vacuum draw from the airbox. Both heads have drains to the crankcase, there is no bypassing the oil drain.