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Discussion Starter #1 (Edited)
6s (V6) PCV Valve Failure, Excessive Oil Consumption

This thread has allot of Good information in it (http://forum.mazda6club.com/3-0l-v6/158303-6s-v6-pcv-valve-failure-excessive-oil-consumpti.html) but it also has some incorrect and misleading information in it. With over 300 posts, you'll never finish reading it. I encourage you to take a moment read some highlights from this same thread regarding what is and what is NOT happening in relation to an engines oil consumption and the PCV valve.

PASTE:

http://forum.mazda6club.com/3-0l-v6/158303-6s-v6-pcv-valve-failure-excessive-oil-consumpti-11.html#post3488634 Post #307
How does the PCV effect oil consumption on the AJ V6 3.0? Like any other engine the Positive Crankcase Ventilation (PCV) valve is NOT the cause of oil consumption!
The diagram below shows the path for the inlet air through the air filter into the Bank2 valve cover via the red hose (bank2 is near the grill). The air is pulled through the engines crankcase from bank2 valve cover (VC) to the Bank1 VC gathering oil fumes (ORANGE). When the throttle plates are closed, the engines vacuum is high and part of the engines idle air is supplied by the PCV through Bank1 VC which is the GREEN hose into the IM.

Again - for all those who wish to blame the PCV valve for oil consumption, NOT ITS FAULT! The engines oil pump feeds oil to the reciprocating components to lubricate and cool them. A by product of this is oil vapor which must be extracted from the crankcase. Hence the need for the PCV system; to remove oil vapor and reduce internal pressure which can cause seals and gaskets to leak. To Reduce emissions those fumes are pulled into the intake track and harmlessly burned during the combustion process. This is pretty standard across all makes and models of 4 storke combustion engines.

Worn out engines with higher amounts of blow-by past the piston rings can raise the pressure in the CC increasing the demand on the PCV. A by-product of this is oil consumption. i.e. normally the oil condenses back into a solid and returns to the sump as "oil" to be used it again and again. However, when in excess, the vapors have no where to go and are litterlay pumped out of the engine as vapor. The PCV is not responsible for rate of consumption, it is a path for oil to be burned by engines with a high amount of blow-by past the pistons compression rings. It is now the RESPONSIBILITY OF THE OWNER TO CHECK AND MAINTAIN THE OIL LEVEL! Just because the oil is rated for 5, 6, and 7,000 mile intervals doesn't mean you can neglect or that a once good engine didn't burn oil of the course of time.

EDIT: I added arrows to show Idle vs WOT throttle. During WOT there is so much oil vapor from oil being slung everywhere - that typically both valve covers are venting fumes into BOTH intake tracks.



If you understand how critical the idle control air is to an engines performance you can see why PCV valves metering orifice is important to idle speed and how sludge build up internal to the PCV valves orifice can change the idle speed making the ECM have to perform corrections to the idle control air at the TB. Hint - not ALL PCVs ar the same as they meter idle speed air and have different orifices sizes for different applications. In short - When the throttle is closed at the TB, the engine is running and idling burning its own fumes from the crankcase. The check valve inside the PCV is to stop back-fires in the intake track from entering the Crankcase and causing a hazardous explosion.

Bottom line: check and change you oil! If it's low after 3000 miles, how low will it be in 7000 miles??





http://forum.mazda6club.com/3-0l-v6/158303-6s-v6-pcv-valve-failure-excessive-oil-consumpti-10.html#post3456895 Post #300 from 09-25-2012

NOT on the band wagon about the PCV valve and hose causing EXCESSIVE OIL CONSUMPTION!!!! It doesn't add up. Its just a half baked idea ran wild!

The valve covers of engines are vented so the oil fumes from the reciprocating components and piston ring blow-by can be vented out of the crankcase so the engine doesn't build pressure internally. Internal pressure from plugged and/or inoperative vents force the oil out through the seals, gaskets, dipstick tube, oil pans seams, etc. If an engine can't breath it will leak oil as the gaskets and seal can only take so much before they begin to seep.

Being a V6 with two valve covers one vent is permanently routed directly to the intake before the TB (fresh air). The other is the topic of discussion and has manifold vacuum to extract the fumes from the crankcase and valve covers.

ON A GOOD ENGINE WITH PROPERLY FUNCTIONING PISTON RINGS and valve seals, one valve cover has fresh filtered air via the air cleaner. Engine vacuum from the IM pulls air through that cover and into the engine block and up into the cover connected to the IM so the fumes can be burned in the combustion process. The only thing the PCV valve does is control the volume because its a metered orifice and act as a stopper when / IF the IM track has combustion (don't want a fire in the crankcase).
PCV = Positive Crankcase Ventilation. POSITIVE meaning we want positive flow so the engine doesn't build pressure inside!

Big TIP when looking at USED CARS; look inside the intake runner for puddled oil! If it has puddled oil, it suggests above average blow by and "**maybe**" the RINGS are worn thus having blow by OR the PCV has been plugged for a long time. The engine is a big pump sucking air into the IM. This keeps the engine crankcase at or near a vacuum state NOT a PRESSURE STATE until reaching high RPMs. If the crankcase has Pressure at idle it means there is MORE blow by from the rings than the PCV can suck in!

A great test is to place some strong cellophane over the oil fill hole and seal it down. If it sucks in while the engine is at idle the PCV is forming a vacuum which is what we want. If it bubbles UP, the engine is building pressure which is not good sign but could be simple fix like the collapsed hose in this thread or the BAD NEWS, an engine rebuild!!! ** DO NOT START THE ENGINE AND REMOVE THE CAP OR OIL WILL FLY OUT EVERYWHERE! ** You need two people!

Is this making sense?


So I ask, how can defective PCV cause you engine fumes to disappear at a rate that does damage? It can't! The problem is NO ONE IS CHECKING THE OIL!!!! The fumes are CONSTANT! Always there! If you don't believe a word I said, wiki PCV Crankcase ventilation system - Wikipedia, the free encyclopedia

Also, i'm going to be brave and ask for a sticky as the other threads opening words could use some correction. Thanks all -
 

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Since this is an oil consumption tread id like to add my experience so far.....when i got my 6 oil would last the 5000km on reg oil....switched to Royal purp lost about a quart+ per change....switched to castrol syntech ...Same as rp but not as bad. Prob just under a quart....Been running mobil1 syn now the last two changes and its still high on the marks.....all oils have been 5w20
 

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Discussion Starter #3 (Edited)
Since this is an oil consumption tread id like to add my experience so far.....when i got my 6 oil would last the 5000km on reg oil....switched to Royal purp lost about a quart+ per change....switched to castrol syntech ...Same as rp but not as bad. Prob just under a quart....Been running mobil1 syn now the last two changes and its still high on the marks.....all oils have been 5w20
Adding to this; I've had oil burners that were lugged about, had misfires and oil fouled plugs which the PO neglected and rairly changed the oil. By doing repeated short cycles on OCI (like 1500 miles) and freely reving it using the entire RPM range and NOT lugging it - the carbon and tar sticking the rings which dropped the compression was cleaned up, they start building compression again and no longer foul plugs.

A plug that doesn't fire does bad things as the required burn uses combustion gases to seat the rings. No flame front = less cylinder pressure to seal the rings. by getting the hole firing again and running lots of fresh oil in it, some will come back to life.

The relationship here is that - blow by past the rings increases crankcase compression and forces oil out somewhere. The path of least resistance is the PCV. EDIT: WHEN I SAY PCV it also includes fresh air to the system. So it still comes down to neglect and NOT paying attention.
 

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Hmmmmm makes me wonder if mine will start burning less oil over time. When i used royal purple it went through about 2 quarts on an 8,500 km OCI.

Now im running AMSOIL XL and it doesnt seem to go through as much but still requires top ups between oil drops. Thinking about running some Mobil1 next time to see if it makes any difference. .


Sent from AutoGuide.com Free App
 

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Discussion Starter #5
I know all these lab tests say leave it for long periods but two things happen. People forget and DON'T check it becuase its not "DUE" and frankly the filters really need changed before 8000 miles. The S's have roller rockers so the oil is not subjected to the "Shear" like a flat tappet cam (the2.3's) and zinc and some other additive are major factors in keeping the shear or wiping contact points from wearing each other down. In most cases that additive is gone long before then. If I had to guess I might have close to 2 million miles driven and NEVER lost an an engine bearing on anything. Then again I run the crapp out of them too. There was 77 F250 I slid some rod and main bearings into because it was neglected. It was replaced a couple years later w/a 460c.i. V8.

Me personally I try to keep the OCI under 4500 miles/7.2k. As I can hear the engines tone change after 3500 and the crap looks nasty. Reason enough for me.
 

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I know all these lab tests say leave it for long periods but two things happen. People forget and DON'T check it becuase its not "DUE" and frankly the filters really need changed before 8000 miles....

...Me personally I try to keep the OCI under 4500 miles/7.2k. As I can hear the engines tone change after 3500 and the crap looks nasty. Reason enough for me.

I personally change our oil and filters at 5,000 mile intervals even using full synthetic or synthetic blends. They don't cost much more than lower quality oils these days and if you're doing it yourself even better money-wise. But even using standard oils, it's well worth the few extra $'s to change more often IMHO...
 

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Discussion Starter #7
Because the original thread is forever long few will read it to the end, can we sticky this one? Also, I'm open to edits if someone finds errors the content. Thanks FI @Mr.Smoke
 

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Woo! Glad my engine loses at most undetectable amounts of oil (for now).
First thing I did to car after taking it home was change oil. I then read the above linked thread and got concerned about oil consumption.. So I went 7000mi before changing again. Still full! Fuck yea.

And yes, both readings were from cold engine.
 

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Great info! I just replaced my engine (129,000 mi) back in January and the one that replaced it (130,000 mi) is consuming massive amounts of oil. I can actually see oil build up at the IM right where the PCV hose connects. If I'm understanding you correctly, a worn engine causes more of the oil vapors to be routed there because of excessive blow-by?
 

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Discussion Starter #11
Great info! I just replaced my engine (129,000 mi) back in January and the one that replaced it (130,000 mi) is consuming massive amounts of oil. I can actually see oil build up at the IM right where the PCV hose connects. If I'm understanding you correctly, a worn engine causes more of the oil vapors to be routed there because of excessive blow-by?
Yes, that is a true statement. What are all of your symptoms and do you mind throwing this back in your original replacement thread so we can keep all the dots connected?

Just becuase an engine burns oil, it doesn't mean it misfires. Well until the plugs foul. It can cause detonation and force the ECm to retard the timing tho.
 

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Yes, that is a true statement. What are all of your symptoms and do you mind throwing this back in your original replacement thread so we can keep all the dots connected?

Just becuase an engine burns oil, it doesn't mean it misfires. Well until the plugs foul. It can cause detonation and force the ECm to retard the timing tho.
A lot of oil in the upper intake manifold, oil leaking from the PCV valve on the valve cover and at the hose on the intake manifold. When I installed this engine, I noticed that the intake ports on the actual cylinder heads were very dark, possibly suggesting that the oil consumption had been occurring for some time before I got the engine.
 

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Discussion Starter #13
A lot of oil in the upper intake manifold, oil leaking from the PCV valve on the valve cover and at the hose on the intake manifold. When I installed this engine, I noticed that the intake ports on the actual cylinder heads were very dark, possibly suggesting that the oil consumption had been occurring for some time before I got the engine.
@80,000 miles here is how the intake tract looked.


PS - there was just a film in the IM and hose before the TB. TB was pretty clean too.
 

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On this engine, it almost looked like there was burnt oil on the intake tracts. Unfortunately I don't have a picture.
 

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6s (V6) PCV Valve Failure, Excessive Oil


A great test is to place some strong cellophane over the oil fill hole and seal it down. If it sucks in while the engine is at idle the PCV is forming a vacuum which is what we want. If it bubbles UP, the engine is building pressure which is not good sign but could be simple fix like the collapsed hose in this thread or the BAD NEWS, an engine rebuild!!! ** DO NOT START THE ENGINE AND REMOVE THE CAP OR OIL WILL FLY OUT EVERYWHERE! ** You need two people!



l -
I did that test today.... nothing happened with the cellophane, it did not go in or out....
Im thinking mb because there is a vent hose that goes to the CAI... and it need to be closed also ?

Have you trie to do that?
 

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I did that test today.... nothing happened with the cellophane, it did not go in or out....
Im thinking mb because there is a vent hose that goes to the CAI... and it need to be closed also ?

Have you trie to do that?
At a glance all is well and things ARE -> as they should be. The PCV system is evacuating at rate equal to blow by rate.

A slight increase in idle speed can change this drastically.

Thanks for a good point of reference! Q? Does your engine consume oil in 4000 miles of operation?
 

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yes... it does , but i think thats piston rings....

she consumes 2 quarts in a week.

look at that :)

 

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On this engine, it almost looked like there was burnt oil on the intake tracts. Unfortunately I don't have a picture.
Since I'm replacing this engine, I'll take pics of the intake tracts and other PCV system stuff.
 

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