PCV valves & oil consumption?

[wavinwayne]

How does the PCV valve affect oil consumption? I hope someone can explain this to me. Today, I replaced the PCV valve on my wife's Expedition 4.6L. For as long as we've owned the Expy, it has consumed oil, between 1.5 - 2.0 qt's of dino every 5k miles. FWIW, I just switched to Havoline full synthetic last week. After reading on BITOG that some folks have noticed their oil consumption dropping after installing a new PCV valve, I decided to give it a shot. The part was only $2.39 @AZ, so I figured "What the heck?" So, to re-state my question: How does the PCV valve affect oil consumption?

 

[The Critic]

The oil can work its way up the PCV hose, causing it to be sucked into the cylinders to be burned. Michael

 

[John K]

Also, if it sticks and doesn't open it will increase crankcase pressure and can force oil out gaskets and seals...

 

[Gary Allan]

Oil consumption can be caused be a defective or poorly designed PCV system. If the baffles in the valve cover are inadaquate to prevent oil migration from oil just splashing/spraying on the port. If it becomes clogged and is seized, the only other natural vent for it is the fresh air inlet ..which may not have the same type of baffling installed. Typically if you have a faulty PCV valve you'll start seeing oil cover your throttle body (assuming that your fresh air vent is routed there).

 

[wavinwayne]

When I removed the OEM Motorcraft PCV valve, the internal parts still moved freely & rattled around just like the new Deutsch one that I installed. What does this mean?......that there was nothing wrong with the MC PCV valve that I removed?

 

[Eric Smith]

I think the intakes on the 4.6/5.4L isn't exactly designed correctly. At high rpms I think it sucks it right out of the engine. There may be other factors unknown to me such as how the oil get to the heads, some blowby etc. Did you turn the pcv valves upside down to compare them? Whenever I replace them I always compare theres always a difference. Eric

 

[kenw]

quote:

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Originally posted by wavinwayne: When I removed the OEM Motorcraft PCV valve, the internal parts still moved freely & rattled around just like the new Deutsch one that I installed. What does this mean?......that there was nothing wrong with the MC PCV valve that I removed?

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not necessarily. blow in it one way and no air should get thru. The other direction should be free-flowing. if air gets thru from both directions, it has a bad seating area and won't seal. But it will still rattle. the no-rattle test is one that is pretty severe, meaing it has to be REALLY bad (ie; jammed) to fail that test! I've never replaced one that didn't rattle. but they all leaked a bit.

 

[TallPaul]

quote:

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Originally posted by kenw: not necessarily. blow in it one way and no air should get thru. The other direction should be free-flowing. if air gets thru from both directions, it has a bad seating area and won't seal.

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Interesting because I have Motorcraft PCVs for all my vehicles. The ones for the F150 and E350 pretty much seal on the blow test, but the Aerostar ('93 3.0) blows both directions, only less in the one direction. I notice the plunger inside is odd shaped like it is made to have some back flow. Guess it is designed that way for a reason. Anybody know why?

 

[Gary Allan]

I think if you had enough push to your blow there, TallPaul, it would shut. They should be able to prevent any potential backfire from entering the crankcase/valve cover. You probably have a spring (curved metal band-leaf) that maintains the gap ..probably to reduce the amplitude of the pulsations.

 

[BlazerLT]

The oil consumption is not from oil being sucked up inthe intake, it is from fuel dilution of the oil seeing the PCV valve is not allowing the post combustion gases to be removed quickly. Diluted oil = more oil burning.

 

[kenw]

Yes, PCV do fail and cause oil to be sucked up and thru the intake. I've pulled several that were literally dripping with oil. And depending on where in the intake it vents, you can see the remnants in there too. Oil dilution and subsequent burning will show up on plugs... and it would only happen if the PCV failed in the CLOSED position, which personally I've never seen happen altho I'm sure it happens. If the plugs are clean and yet you are still using oil, the PCV is a good suspect.