Massive oil consumption from towing a trailer

[Brad_C]

Originally Posted By: zray
However, under the full load condition, flow is minimal because the crankcase pressure does not move a significant volume thru the pcv system in comparison to the flow generated by a vacuum.


What a load of horse hockey. The "volume through the PCV system" is mostly comprised of blowby and blowby is at its maximum at full load when you have no vacuum.

 

[zray]

Originally Posted By: Brad_C
Originally Posted By: zray
However, under the full load condition, flow is minimal because the crankcase pressure does not move a significant volume thru the pcv system in comparison to the flow generated by a vacuum.


What a load of horse hockey. The "volume through the PCV system" is mostly comprised of blowby and blowby is at its maximum at full load when you have no vacuum.


Wrong. Although blow by is at its greatest when the engine is under full load, it isn't moving thru the PCV system in any great volume for two reasons
1) the PCV valve is mainly closed in that scenario
2) without a vacuum the blow by gasses are just relying on crankcase pressure to move thru the partially closed valve.

This is why many race cars have an exhaust crankcase evacuation system, they work ALL time to effectively reduce crankcase pressure, especially during times of little to no vacuum when a PCV system isn't doing much to relieve crankcase pressure. Think about it, If the PCV system was effective at relieving crankcase pressure these racers would not be going to the trouble to plumb an exhaust crankcase evacuation system, would they ?

The PCV doesn't need ANY blow by to move a significant volume of air thru the valve. Most of the time clear air is being circulated thru the PCV system, and not much blow by from the combustion process. There is a clean air source thru the air cleaner for. The PCV system to pull from, and that's where the air comes from that is circulated thru the PCV system.. Perhaps that's where you are confused ?



Z

 

[Shannow]

Originally Posted By: zray

1) the PCV valve is mainly closed in that scenario


It's OPEN...OPEN, as OPEN as it can be.


Originally Posted By: zray
2) without a vacuum the blow by gasses are just relying on crankcase pressure to move thru the partially closed valve.


If there's enough crankcase pressure to force gasket and seal leaks, there's enough pressure to drive those gasses through the OPEN PCV and into the manifold.

 

[Shannow]

You don't shop at one of those busy little ones do you ???

How can you have gone fishing for that picture, and completely ignored the ones that explain PCV operation ???

this one has an engine pic as well

http://www.aa1car.com/library/pcv.htm

 

[TFB1]

I fully agree with Shannow's diagrams and I'm a old Ford guy as well... Own a '69 428 Cobra Jet Torino(at least one since '73) & '72 302 Comet, with PCV configured to '67 models(IE open breather cap)

 

[440Magnum]

Originally Posted By: Shannow


Again...nope...

http://www.autocarepro.com/pcv-system-sometimes-things-just-have-to-suck-to-be-right/


Hard science over intuitive speculation for the win. Thanks for the graph, Shannow. I will add that Zray is right about one thing- at WOT/low RPM (the left-mostl, lowest manifold vacuum side of the graph, an engine-lugging condition) the blow-by and PCV curves cross- and that is where the PCV can't "keep up" with blow-by, the crankcase is subject to positive pressure, blow-by will exit through the PCV make-up inlet as well as through the PCV valve, and any leaky gasket will likely leak worse.

But it is ABSOLUTELY TRUE that even under that condition, the total volume flow through the PCV and into the intake is *higher* than at idle/light load, and it is also "dirtier" with both blow-by and oil mist.

This assumes the more common PCV valve, not a fixed-orifice CCV system like a Jeep 4.0 and relatively few other vehicles use.

 

[Gokhan]

In any case, if the oil consumption was too high with respect to normal driving, the engine was being overstressed. Perhaps it's just the PCV or perhaps the rings unable to keep up with the RPM, or perhaps the oil being too thin for the driving conditions, or a valve-stem oil seal issue. Regardless, you should have taken corrective action instead of risking engine wear, which could have been to use thicker oil, drive slower in lower gear, check the PCV valve for cleanness, etc.

 

[Shannow]

Originally Posted By: Gokhan
In any case, if the oil consumption was too high with respect to normal driving, the engine was being overstressed. Perhaps it's just the PCV or perhaps the rings unable to keep up with the RPM, or perhaps the oil being too thin for the driving conditions, or a valve-stem oil seal issue. Regardless, you should have taken corrective action instead of risking engine wear, which could have been to use thicker oil, drive slower in lower gear, check the PCV valve for cleanness, etc.


Gokhan,
that's why I posted a link to actual causes of consumption.

Originally Posted By: Shannow
OP, found this which may help

http://ftp.astmtmc.cmu.edu/docs/gas/emissions_task_force/minutes/20060504/sae2004-01-2909.pdf

Again, I think it's your towing (load), and RPM...nothing to worry about.

Joe90_guy fig 19 describes you test...difference in consumption between oils of differing volatility.


The PCV thing was trying to correct a misleading series of statements.

 

[Gokhan]

Good reference, thanks.

 

[zray]

Really now, none of those illustrations have a passing resemblance to an actual PCV valve cone taper, which provides a much different operation that your simplistic explanation is capable of conveying.


Z

 

[Shannow]

Originally Posted By: zray
Really now, none of those illustrations have a passing resemblance to an actual PCV valve cone taper, which provides a much different operation that your simplistic explanation is capable of conveying.Z


Have at it then...find something reputable that backs your assertions, not just your imagined operation.

Pan evac systems (how many times did you bring them up ???) do NOT prove your assertion, they have other reasons than PCV.

 

[zray]

Originally Posted By: TFB1
I fully agree with Shannow's diagrams and I'm a old Ford guy as well... Own a '69 428 Cobra Jet Torino(at least one since '73) & '72 302 Comet, with PCV configured to '67 models(IE open breather cap)


Not to nitpick, although that is the common form of warfare here, Ford went to a closed breather system for all models in late '66 production.

Z

 

[OVERKILL]

 

[Shannow]

OVERKILL,
I don't know why so many people would put so many versions of the wrong thing in service and maintenance manuals...an no-one seems to have anything on the "real" mode of PCV operation.

 

[OVERKILL]

LOL!!!!

 

[Merkava_4]

I'm absolutely amazed nobody is disagreeing with my above statement. I was just throwing it out there to see what happens.

 

[zray]

We're all LOL, in my case at how easy it is get a rise out of the experts here. Don't you know when you're being had ?

Z

 

[TFB1]

Originally Posted By: zray
Originally Posted By: TFB1
I fully agree with Shannow's diagrams and I'm a old Ford guy as well... Own a '69 428 Cobra Jet Torino(at least one since '73) & '72 302 Comet, with PCV configured to '67 models(IE open breather cap)


Not to nitpick, although that is the common form of warfare here, Ford went to a closed breather system for all models in late '66 production.

Z

In CA but not in remainder of US, I know 289s used a funky cap plumbed into air cleaner for Calif...

Chrome cap on my 302 is for 1967 390GT or 289 Hi-Po(my '67 Falcon 289 had same cap but was painted)... Eons ago I used them on 428CJ, now reverted back to closed cap for show... Comet is a resto-mod, originality is secondary...

 

[zray]

Before 1966 their was a difference in the PCV systems for the CA market and. The rest of the USA. Late '66 and later all the Fords used the closed PCV system. Aftermarket vendors do not have this correct.

Z

 

[TFB1]

Originally Posted By: zray
Before 1966 their was a difference in the PCV systems for the CA market and. The rest of the USA. Late '66 and later all the Fords used the closed PCV system. Aftermarket vendors do not have this correct.

Z


Is that so??? How come 45 years ago I was buying same cap at dealer for '67 428 Shelby???

Plus as I already mentioned my '67 Falcon used same painted version of this cap, sorry I'm gonna believe what I've seen...