PCV Valve?

[Rearanger]

Been doing injector work and replaced the valve cover gaskets. With the intake off I found a fair amount of oil film inside the intake.

I noticed this a while ago and installed a catch can but this did nothing and I have removed it. I really can't have any excessive blow-by as the compression is as new at about 195. I've also tried to detect extra pressure in oil dipstick tube but nothing there. The valve cover has the oil separator in it.

The PCV was replaced a while ago with aftermarket and recently I thought maybe returning to a Motorcraft would be better. When I compared the operation of the dealer PCV with my aftermarket they performed the exact same, so the OEM was not worth the 4x the cost.

Discussions on the web are everywhere on this and I think it a natural occurrence of oil vapors and PCV systems. I know my Camry does this as well.

There is no measurement on what's normal so maybe I just need to suck carb cleaner into the manifold every 6 months to keep the system clean. With the system apart I have flushed and cleaned the intake.

I have not been able to find a better PCV, if that would help, except maybe a Wagner at about $150 for racing engines.

Would like some feedback on this if possible.

 

[RonD]

What kind of oil are you using?

Blow-by is normal and happens on all piston engines, the oil vapor comes from this blow-by.
When the hot combustion gases "blow-by" the piston rings it vaporizes some of the oil on the rings/pistons and cylinder walls.
The oil that lubes bearings and valve train squirts out so doesn't really add much to "vapor" in crankcase and valve cover area, it settles out pretty fast.

A good quality oil will produce less vapor than a poor or medium quality oil.

PCV valve functions opposite of what many think, it is vacuum operated but opposite of vacuum pressure, high vacuum(idle) closes the PCV valve, lower vacuum(accelerating and higher blow-by) opens it more.
If PCV Valve isn't operating correctly then it can cause more oil vapor to be sucked in to intake when vacuum is higher.

You also need good fresh air flow from vent hose(oil filler tube on 3.0l I think).
This can help prevent condensation, a little will always happen, but as long as engine coolant is being warmed up to 200degF, normal operating temp, the water/oil mix should burn off within 10 minutes of driving.
If you are driving mostly shorter trips, under 15minutes, then the residue in the intake could be from condensation build up in the valve cover area, this causes a higher volume of water/oil vapor as it heats up which is sucked into intake, water is evaporated but oil remains behind.

One thing that is often over looked is the exhaust valve guide seals, your mentioning of Toyota reminded me of that, these seals can get hard from the heat and not seal as well, hot exhaust gases come up the guide and vaporize oil on the valve stem and seal, adding to the vapor in valve cover area.


Some of the more expensive PCV Valves are heated, which is a benefit if you live where there are long cold winters.

 

[kimcrwbr1]

I just use the cheap ones and chane it with every oil change they are cheap.

 

[Rearanger]

Spec'd oil is 5w-20, I'm using Mobile1 0w-30.

On value cover with oil cap (PS) there is separate vent tube to intake hose. No real oil in there and with it's own baffle.

My PCV is heated with coolant. I live in NC so cold weather start/run is limited. When I removed the valve covers the lifters/etc. were like factory new. I run Amsoil dual by-pass filter system with 3 micron filter and Pure1.

Believe me my oil is pristine.

 

[RonD]

Synthetic oils should produce less vapors, but in your case it doesn't seem to be the case, and with no oil recovered in a PCV catch can, I am puzzled on the source of the oil residue in the intake.
Was the residue from throttle body and through out upper intake?
With vent hose not showing signs of oil it would mean PCV could be drawing to much air, but catch can should have shown that.

 

[Rearanger]

I just use the cheap ones and chane it with every oil change they are cheap.

It's not as if these are precision valves. All metal with very loose flat poppet inside. If it's tipped off vertical slightly it opens slightly, there is no positive seal. Most of the closing pressure is the weight of the poppet as the spring just seems to provide a bias. All the valves I've looked at, even Motorcraft, perform the same and price ranges from $17 for OEM to $1.95 for one at AutoZone.

Was the residue from throttle body and through out upper intake?

The PCV is attached to a long pipe that extends most of the way into the top of the plenum, and ends just on the downside of the throttle body. There's a special mould cavity cast into the intake plenum. After the end of the pipe the whole plenum had an oil coat to it. As I stated in another post the injectors had a black residue around the non spray part of the tips that must be oil building up from hot gases there. The lower intake must also be coated.

With vent hose not showing signs of oil it would mean PCV could be drawing to much air, but catch can should have shown that.

When I used the catch can it did catch oil and water, but there was still oil getting into the intake.

I will say that in winter here, the truck, on two to three days a week, only goes about 2 1/2 miles and barely gets warm as I drive to my buddy's house where he drives us to the gym. We alternate 2 days one week and three days the next where the engine will get to full operating temp to make the 18 mile distance.

Other than that the truck gets used for full warm operation. When I pulled the valve covers as mentioned, no white-ish build up at all. My oil cap also is always clean as is the dip stick.

 

[Rearanger]

Apparently the PCV works most when on high vacuum at idle. Is it possible my vacuum at running rpms is too high at the PCV inlet? Higher rpms would splash more hot oil around.

Not sure how I'd test this or adjust it if I could. I have vacuum gauged the inlet a fair while ago and it was normal.

 

[Rearanger]

Also, nobody can say this isn't normal. My spark plugs all have zero oil residue whenever I've inspected them.

 

[RonD]

PCV Valve closes more at high vacuum, opens more at low vacuum.
The old "rattle test" for PCV valves was to see if the weighted valve and spring were free to move, high vacuum level pulls the weight up closing the valve, weaker vacuum lowers the weight, opening valve more.
Since all 4-stroke gas engines have the same vacuum specs for the most part, all PCV Valves are pretty much the same in when valve opens and closes.

And yes, if your valve was out of spec then it could be open more than it should be at idle or deceleration(very high vacuum) which would cause too much oil vapor to be pulled into the intake.

If you wanted to test PCV Valve flow you would need to test vacuum in valve cover or crankcase while driving.
You may be able to remove dip stick and use a vacuum gauge on it's tube, with hose into cab.
Or make a fitting to go between PCV valve and valve cover with a port for vacuum gauge.
Pay attention to deceleration or going downhill in gear using engine as a brake, that's when engine vacuum is highest and there should be no PCV valve flow or very very little.
Never tested this before so don't have any specs for what you should see.

 

[Rearanger]

I set up a test of the crankcase pressure.

I found a small vacuum gauge from a "MityVac", goes from zero to 45" hg, so a smaller scale than my large vac gauge. I drilled and tapped the oil filler cap for a brass fitting and attached the small vac gauge to that so I could measure crankcase pressure. I also attached my large vac gauge to a connection downstream of the throttle body, right where the throttle body attaches to the intake plenum.

At idle my engine vac was 18.5" hg and the crankcase vac did not move off zero. Increasing the rpm did not increase the crankcase vacuum/pressure. Opening and closing the throttle quickly gave me 2"hg to 24"hg on the large gauge. All pretty much textbook vac readings.

I then plugged the vacuum line to the PS valve cover. This is the line that is meant to replace pressure drawn out by the PCV. The crankcase vacuum slowly dropped to about 4"- 6" hg until I released my thumb and a rush of air returned the crankcase pressure to balance.

I think this is how the PCV system is supposed to work. I'm not getting excess vacuum that would draw oil fumes into the intake and upset my idle fuel trims , or am I getting pressure inside the crankcase.

This probably a good way to test a PCV system.

 

[RonD]

Yes, it all reads correct, but you would/should get vacuum in valve cover area under load, in static test you get very little.

 

[Rearanger]

Ron, not sure I understand you.

Idle is closed throttle and high vacuum, load is open throttle low vacuum. Under load what vacuum readings would I be looking for?

And if the fresh air replenish connection from the intake is replacing what the PCV is sucking out how does open throttle make any difference to crankcase pressure/vacuum?

 

[RonD]

PCV valve is almost closed when vacuum is high, the vacuum pulls valve closed against a springs pressure trying to open it, blipping the throttle open to 0 vacuum probably wouldn't show valve cover vacuum because it is such a short duration, engine RPM catches up with throttle opening pretty fast .
When engine is under load low vacuum is sustained for a longer period, i.e. those Fuel Economy dash mounted vacuum gauges, where you try to keep needle in the Green, lol.
Engine RPMs take awhile to catch up to throttle position, and they never do if going up a steep hill.
Under load is also when you would get the hottest cylinder temps so the most oil vapor in the blow-by.
And the Vent hose can also serve as an outlet for blow-by pressure if vacuum gets too low under load, this is why it is not just Vented to outside air, but connected to air filter housing or air plenum(air tube) connected to throttle body, any overflow blow-by pressure would also go into intake to be burned same as if it went thru PCV Valve.

 

[Rearanger]

Vacuum gauge reacts immediately when engine rpm changes.

The PCV seems to have closed in the up position and a closed in the down position. Valve should "dither" or else you risk stalling the engine from too large vac leak. Also valve is not a positive open or close, it's just not built with that precision and has built in leakage.

Seems blow-by would have to be very extreme to produce back flow in fresh air intake.

 

[RonD]

I was speaking about the vacuum gauge on the valve cover area which you said didn't react much with static RPM changes.

In early the '60's Open PCV valve systems were first used, this was in response to the oily roads and pollution from breather tubes on the upper oil pan or lower block that vented blow-by/oil vapor out and down at the ground.

Open PCV valve system just had a filter cap on the vent tubed, and under high load any blow-by and oil vapor could still exit the system via the Vent hose, yes it can get that much pressure from blow-by if engine is under load.

Because of this, Closed PCV valve systems started in the late '60's early '70's, these put the vent hose in the air cleaner housing sitting on the carb, so any overflow vapor would be sucked into the carb.

When engine is off PCV valve pintle slides down and closes the air way at the bottom of the valve, when engine starts vacuum sucks it up and open but there is a tapered end that restricts air flow when it is pulled up that high.
As engine load increases vacuum decreases and the pintle slides down opening the air passage more and more as the tapered end drops.
If engine has enough of a load vacuum can go to 0" and pintle will close just like engine was off, at that time blow-by would be high and would exit out the vent hose.
On older high mile engines that could happen sooner than later, they have lower vacuum and higher blow-by which is the same thing really, lol, that extra pressure will tend to push up on the bottom of the PCV valve, keeping it open, but path of least resistance with 0" vacuum would be vent hose

The PCV valve's vacuum "leak" is compensated for when you tune a carb or when they setup parameters in fuel injection computer, which is why it is best to use the correct PCV valve for the engine.