How Do I Test a PCV Valve?

Although the internet abounds with articles that describe in some detail how one can test suspect PCV valves, the simple fact is that there are no reliable methods to test PCV valves in general or to test the calibration settings of any given PCV valve to ensure that it (still) works as expected on the engine it was designed for, in particular. 

One example of a test method that is commonly retold on the internet involves cleaning a PCV valve with a suitable solvent, and then shaking the valve to see if it “rattles”, presumably to verify that the valve is not stuck open or closed. However, the fact is that if a PCV valve “rattles” when one shakes it, the moveable part that keeps the valve closed is no longer held in position under spring tension, which means that the valve is actually defective and useless.

As a practical matter, the spring in the valve should hold the moving parts of the valve closed so tightly that no amount of manual shaking will cause the valve to “rattle”.  As proof of this, we submit that new OEM and OEM-equivalent PCV valves do not “rattle”, no matter how vigorously one shakes them.

One other commonly advocated method of testing a suspect PCV valve is to clean it out with a suitable solvent, and then to suck on the outlet port to a) verify that the valve is not stuck closed, and b) to verify that air can flow through the valve in only one direction.

At first reading, the “suck” test might appear to be a reasonable one, but the problem is that since PCV valves are calibrated for specific applications, there is no reliable and/or accurate way to replicate the vacuum that will overcome the calibrated spring tension. Thus, sucking on the valve until it opens holds no diagnostic value, since this method takes no account of the PCV valve’s calibration settings.   

So what does the above mean in practice? It simply means that when an engine operates smoothly and it has no unexplained or persistent oil leaks, it is highly unlikely that there is anything wrong with the PCV valve, which obviates the need to perform inaccurate and largely useless tests on the PCV valve.

Nonetheless, if the engine has been running progressively less smoothly, both the fuel and oil consumption rates have increased, or if sudden and persistent oil leaks have appeared, the PCV valve might likely be defective in some way, since these symptoms are common effects of failed or defective PCV valves.

However, these symptoms can also have many other potential causes, so to avoid possible misdiagnoses and unnecessary repair bills, we recommend that you replace the PCV valve on your engine at least once a year to ensure that the PCV valve always works optimally, which, if nothing else, will largely eliminate a defective PCV valve as a possible cause of the symptoms described here. 

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