PCV Valves - Crankcase Ventilation System

Phil Ramsey

Pollution of the crankcase oil increases each time the spark plug fires. The by-products of the gasoline and air explosion are primarily carbon monoxide, nitrous oxides (NOx) and unburned hydrocarbon by-products. Some of these products are forced around the piston rings and down into the crankcase; these are called blow-by products. These gases mix with the oil vapors in the crankcase and immediately begin to cook up some nasty substances that can, and will, harm your engine.

We must remove the blow-by products from the crankcase. But we cannot just vent them to the atmosphere. So what do we do?

Until 1965, most cars and small trucks had a vent, often called a road draft tube, which vented the crankcase to the atmosphere. After 1965, legislation brought forward a governmentally mandated device to be installed on all vehicles.

What is a PCV Valve?

PCV ValvesThe positive crankcase ventilation (PCV) valve is a simple system that introduces filtered fresh air into the crankcase. The PCV valve uses the engine’s vacuum to pull air through the crankcase and reintroduce it back into the intake manifold system. This sends the uncombusted hydrocarbons and nitrous oxides that blew by the rings another chance for complete combustion, and in later vehicles, to be managed by the engine’s emission control system.

This system works great and is practically maintenance-free. However, a lack of knowledge coupled with the fact that the average driver does not open his engine hood at every fill-up, can lead to large problems. And, not knowing how and why the oil breathes can lead to expensive repair bills for your vehicle.

About the time we ceased handing out used oil for dust control, I learned that wine, like oil, needs to breathe. One summer during my youth, a friend and I realized that we could make wine from the locally grown oranges.

Incidentally, there was a large commercial orange winery within two miles of my home. How hard could it be? We were too young to legally purchase wine, so we “borrowed” oranges for educational purposes from a grove next to my home.

To begin the wine-making process, we juiced the oranges, filtered the pulp, and then placed the juice and yeast into three large five-gallon glass bottles. They were the kind of bottles in which spring water was once delivered. We tightly corked and even manufactured a rudimentary cage for the cork, like the ones we’d seen on champagne bottles.

Too bad we were ignorant of safety valves or pop-off valves.

PCV Valve LocationWe stored the bottles in my friend’s attic, out of his parents’ sight. One fine day, the yeast and sugars from the juice performed as one might expect and blew the corks off the bottles, spraying rancid orange wine throughout my friend’s attic.

The smell was awful. Our mothers were livid and it took us two days to scrub everything to get rid of that rotten smell. It was a simple mistake, but the consequences of our ignorance were severe.

The consequences of ignorance about PCV systems can also be costly. The system is simple. As a professional mechanic, almost every week I see a malfunctioning PCV system literally grinding an engine to bits. The rubber hoses and grommets that are part of the system can swell and loosen their connection to the other parts of the engine. The results depend upon where the integrity of the connection fails.

If the connection is loose and sucking air into the line between the air filter housing and the valve covers or other intake point, raw unfiltered air is introduced to the crankcase. This can grind bearings, overload the oil filter capacity and in general, make a junk pile of the engine. Many of the prematurely worn out engines I have seen can trace their failures to a long-term malfunction of the PCV system.

If the connection fails on the other side between the PCV and the intake manifold, raw blow-by products spew into the atmosphere. The results are the terribly messy, oil and dust-coated engine compartments that many of us have seen, and the release into the atmosphere of many aggressive pollutants.

The ignorance and lack of attention to detail made my first wine experience my last. Don’t let the lack of knowledge and disregard for the simple PCV on your car cost you many miles of service from your modern-day combustion engine. Either you or your mechanic can inspect this entire system in just a few minutes. Hose, grommet or PCV replacements often cost less than $20. Do yourself and the environment a favor - check and/or repair this vital system this week.

Try this for yourself: Check under the hood for a white plastic sticker, approximately 6 by 3 inches. Listed on it are the engine size, emission systems in use, spark plug gap, timing information and other useful information. Part of the sticker looks like a road map with colored lines.

Look for PCV, ignoring the strange acronyms, such as EGR, MAP or VSERV. If you can locate the PCV valve on the engine, follow the map and check all hoses and connections for swelling or cracking. Replace any parts found loose, cracked, swollen or coated with motor oil. In general, if there is no evidence of oil leakage, there should be no problem. Malfunctioning PCV valves can be the source of a leak and can cause leaks in other gaskets on your engine. If in doubt, see a professional.

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