Educate me on oil and the PCV system

[GearheadTool]

How does oil function in relation to a car's PCV system?

Under normal circumstances, is oil not "sucked out" akin to a vacuum?

Would oils that "clean" also clean the PCV system, if this were the case?

Thank you!

 

[eljefino]

Only the volatile stuff in oil winds up in the PCV system. This includes gas and water that winds up in there due to combustion as well as by products of making the oil.

This has been the subject of much research and improvement over the years.

An oil that cleans won't clean your PCV. Consider its evaporation to be a sort of distillation. Most stuff that evaporates out, you don't want, and hope the engine combusts it without it sticking. IMO this is why throttle bodies have teflon coatings etc.

 

[jrtribology]

Yeah I'm curious about that too, when I put a new PCV valve in my 1986 caprice quasi 9C1 LM1 350 and it prevented hesitation of the line for a couple minutes and then it went back to the way it was. What is better Positive Crankcase Ventilation or just baffles comming out of the valve covers ?

 

[jrtribology]

I know one thing if ther isn't some kind of ventilation the gaskets will blow !

 

[eljefino]

Working PCV is far better, it keeps oil mist outside the engine down and supposedly helps the rings seal better.

In the old days they used a "road draft tube" which basically kept the middle of every lane on the freeways a nice black color and made it greasy in the rain.

PCV was one of the first emissions controls, circa 1962!

 

[Phishin]

Originally Posted By: eljefino
it keeps oil mist outside the engine down and supposedly helps the rings seal better.


Not really sure what this means.....

But all it really does is suck mostly combustion gases and some oil mist out of the heads and recycles it through the intake.

This does two things: 1.) It is better for the environment--like it was stated earlier, this tube used to simply vent under the car. 2.) Recycling these combustion gases back through the intake increases the effective octane rating of the intake air/fuel mixture, helping to prevent pre-detonation/pinging/engine knock.

 

[kam327]

Originally Posted By: Phishin
But all it really does is suck mostly combustion gases and some oil mist out of the heads and recycles it through the intake.


Don't you mean the crankcase?

 

[daves66nova]

Originally Posted By: eljefino
In the old days they used a "road draft tube" which basically kept the middle of every lane on the freeways a nice black color and made it greasy in the rain.
A lot of 18-wheelers still have these tubes.

 

[mechtech2]

There is an oil separator/baffle so liquid oil is not sucked through.

 

[Phishin]

Originally Posted By: mechtech2
There is an oil separator/baffle so liquid oil is not sucked through.


In theory, but it does. Sometimes quite a bit of oil get sucked up. That's why people install catch-cans on this plumbing....to prevent excessive oil from being introducted into the intake.

The oil drops to the can, yet the gases continue on to the combustion chamber.

 

[eljefino]

Originally Posted By: Phishin
2.) Recycling these combustion gases back hrough the intake increases the effective octane rating of the intake air/fuel mixture, helping to prevent pre-detonation/pinging/engine knock.


No, it doesn't. It's a necessary evil (emissions) and too much oil will cut your octane. I rebuilt my saturn engine exclusively because the oil burning (quart in 450 miles) was cutting my octane and the knock sensor was cutting my power.

I have to say, it worked.

You may be thinking of EGR systems, which uses the inert-ness of the exhaust air and lack of oxygen to cut peak combustion temps.

 

[Boomer]

True on lowering octane. Any long linear hydrocarbon molecule like oil has a MUCH lower octane rating than a globular hydrocarbon like iso-octane. SO adding oils to the cobustion chamber can start to drop the octane rating if enough are present like the Saturn owner stated.

 

[440Magnum]

PCV is almost 100% a good thing for engines- positively drawing blow-by out of the crankcase and drawing cool/fresh air in reduces sludging and acidification of the oil, and it keeps the blow-by from going into the environment.

The main downside comes from poor implementation that lets liquid oil (mist/spray) get drawn into the PCV system and thus the intake, which lowers effective octane and wastes oil. A secondary downside is dirtying of the intake manifolding, which is a bigger problem in DI engines than conventional but can still lead to stalling due to dirty throttle plates in conventional EFI systems. Only carburetors and TBI flush fuel through the WHOLE intake and thus keep it all clean.

 

[mechtech2]

Originally Posted By: Phishin
Originally Posted By: mechtech2
There is an oil separator/baffle so liquid oil is not sucked through.


In theory, but it does. Sometimes quite a bit of oil get sucked up. That's why people install catch-cans on this plumbing....to prevent excessive oil from being introducted into the intake.

The oil drops to the can, yet the gases continue on to the combustion chamber.


I use zero oil, yet my catch can needs frequent draining. Your theory is wrong.

 

[oldhp]

I think the best PCV system would be hooked into the exhaust system right after the cats with a venturi type system. The heat from the cats would burn the oil/water crud up.
No intake oil puddling.
No crud on piston tops.
No crud on intake valves.
Maintenance free.
Just my thoughts.

 

[electrolover]

Originally Posted By: oldhp
I think the best PCV system would be hooked into the exhaust system right after the cats with a venturi type system. The heat from the cats would burn the oil/water crud up.
No intake oil puddling.
No crud on piston tops.
No crud on intake valves.
Maintenance free.
Just my thoughts.


Racecars run a version kinda similar. But they are running open header with no back pressure. Otherwise they would pump exhaust gasses into the crankcase

 

[KitaCam]

a pcv valve after 100k miles...NOT the way it should look...

It cleaned up fine and has been reinstalled to see how the current oil will effect it after 4k miles

 

[DBMaster]

Actually, I don't think it looks too bad for 100,000 miles. It only matters if the parts inside are still moving. If you got it cleaned up it'll probably go another 100,000.

 

[Phishin]

Originally Posted By: eljefino
You may be thinking of EGR systems, which uses the inert-ness of the exhaust air and lack of oxygen to cut peak combustion temps.


Are you freakin' kidding me? I can't believe I had such a brain [censored]. You are 100% correct. Here I am, trying to educate The Tool about the PCV system, and I'm talking about EGR. Wow. I guess my mind has a mind of it own.

Ooops, sorry fellas. I was real wrong on that one. Jeeez.

 

[RamFan]

Originally Posted By: mechtech2
Originally Posted By: Phishin
Originally Posted By: mechtech2
There is an oil separator/baffle so liquid oil is not sucked through.


In theory, but it does. Sometimes quite a bit of oil get sucked up. That's why people install catch-cans on this plumbing....to prevent excessive oil from being introducted into the intake.

The oil drops to the can, yet the gases continue on to the combustion chamber.


I use zero oil, yet my catch can needs frequent draining. Your theory is wrong.


How can you use zero oil while also needing to frequently drain your catch can?