I know what the PCV valve does and why it's there but it seems to me it's one of those unnecessary parts that were mandated by the "save the earth" people.
Now if I was to replace the oil filler cap on the valve cover with a vented one like we all used to have, the crankcase would never build up pressure and the whole valve thing is moot.
Yes, I know I'm going to kill the planet.
No, it is quite necessary. Aside from the pollution issue of dumping crankcase fumes out into the atmosphere, the road draft tubes in use before PCV was employed (which was around 1960 or so) did not do a good job at all of ventilating the crankcase which is one of the reasons why engines didn't last as long back then. Some of the very early PCV systems had problems but today it's a well-understood, well-developed feature.
This photo illustrates the "crankcase ventilation system" on a 1959 Rambler 195.6 OHV straight-six engine, which is typical of pre-PCV engines. The pipe coming out of the side of the engine circled in yellow just dumped vapors out onto the road, depending on the draft from the car's motion to draw them out:
About the only time you really see PCV problems on modern engines is when there's a change in engine technology and the PCV system doesn't keep up. This happened when engines transitioned to using low-tension piston rings, on some makes this led to severe sludging issues and engine failure due to the increased blowby. We're also seeing this on some GDI engines where the PCV system is not adequate to prevent oil dilution/contamination. (Thankfully none of my vehicles have those "features".)
Yep, I agree!
Even on a modern high-tech non-GDi engine, the “crankcase emission control system” is just a small hose with a valve…
(Link to the image from my cars’ service manual:)
I understand all that about the draft tubes but what about replacing the non-vented oil filler cap with a vented one?
For a technical question such as this, you really need to provide specifics. A 70's era car might not care if you start modifying the emissions system. A modern car will , at best complain, and at worst not run properly.
I understand all that about the draft tubes but what about replacing the non-vented oil filler cap with a vented one?
The engineers who designed your engine made the PCV system an integral part of it. Stick with the type of oil filler cap your engine is designed for or your crankcase ventilation system may not work properly, possibly leading to oil dilution, seal damage, or other unintended consquences.
Chuck, if one puts a catch can in the system (for DI-only engines), could that disrupt the crankcase ventilation system?
Don't know, I've never dealt with a DI engine. I would say if it doesn't block flow of crankcase ventilation and doesn't add extra air it's probably OK.
It depends on how the dams and baffles are set up in your valve cover. Some have fairly elaborate passages and dams to direct blowby to the PCV port while others are just wide open. Older, cabureted vehicles had a breather tube from the valve cove, through the PCV valve into the intake manifold. They also had a second breather tube running from another location on the valve cover directly into the air cleaner with no PCV valve. If you do put a vented oil fill cap on, be sure to wipe down your valve cover a lot because it will be coated with scum.
I understand all that about the draft tubes but what about replacing the non-vented oil filler cap with a vented one?
on what vehicle?
I'm glad I asked. Thanks Chuck. Guess I'll forget that idea and just put a new PCV valve in.