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The Importance of PCV Maintenance

Friday, February 1, 2013

Have you ever maintained a truck on PM for several years and eventually pull the valve cover off in the shop and have the oil all gummed up and stuck to everything? Your first thought is usually – “that damn PM guy must have never changed the oil!” This may be true, but closer examination may surprise you. Neglect of an engine’s PCV valve is common and may be the reason for that gummy oil. Although PCV valves were around in the Continental engine days, they were not as critical as they are now. The overhead camshaft Mitsubishi and Mazda engines found in many different forklift brands are the most critical for PCV maintenance. Seasoned forklift technicians may not realize the importance of the PCV valve maintenance in today’s engines. The following article will explain the purpose of the PCV valve and why your service technicians should follow the routine maintenance intervals.

Prior to the 1960s most engines vented directly into the atmosphere through a vent tube. A California professor revealed that one of the primary sources of smog were hydrocarbons from
gasoline powered automobiles. The solution to the problem was the PCV valve which stands for Positive Crankcase Ventilation valve. In typical fashion California was the first state to mandate the installation of the PCV in the early 1960s. This system slowly
went nationwide by 1966.

The PCV valve is a “one-way valve that ensures continual refreshment of the air inside a gasoline internal combustion engine’s crankcase.” As an engine runs the crankcase begins to collect combustion chamber gases which leak past the piston rings. These gases contain compounds that are harmful to an engine. If these compounds are allowed to gather in the crankcase they become concentrated and form corrosive acids and sludge in the engines interior surfaces. This can harm the engine as it can clog small inner oil passages, causing engine overheating, poor lubrication, and high emission levels. A working PCV valve keeps the crankcase air as clean as possible which helps avoid engine failures.

The PCV valve connects the crankcase to the intake manifold from a location opposite the breather. The Mitsubishi and Mazda’s are located on the valve cover opposite side of the breather. The valve is simple but performs a complicated function. An internal ball or cone style restrictor is held in the normal position with a light spring. The full size of the PCV opening is to the intake manifold with the restricted side towards the valve cover or crankcase. When the engine is running the tapered cone end is drawn towards the opening. By restricting the opening proportionate to the level of engine vacuum vs spring tension the valve changes with different throttle levels. At full throttle there is nearly zero vacuum. At this point the PCV valve is nearly useless and most combustion gases escape via the breather tube where they are drawn in to the engine’s intake manifold anyway. The objective is to redirect or recycle the engine’s blowby via sending it back into the intake.

Since its functioning is very basic it is critical that the PCV valve system be kept clean and open. Incorrect air flow or a plugged or malfunctioning PCV system will eventually damage an engine. Isn’t it great when you do PM’s for $50 flat rate and then have the camshaft seize due to a lack of lubrication? Or when you lose an account because the customer has an in-house technician pull the valve cover and it’s full of sludge. Or just the minor customer complaint “the engine never used to tick that loud?” Both of these tend to look poorly on the quality of your dealership’s PM program. Much of this can be avoided if your road technicians stock the $5.00 - $15.00 PCV valves and remember to change them.

PCV valve flow rates differ between engine models, the installation of an incorrect PCV valve may cause engine stalling, rough idle and other drivability complaints. Never install universal type PCV valves. Typical maintenance schedules for gasoline engines are to replace the PCV valve whenever spark plugs are replaced. The long life of the valve despite the harsh operating environment is due to the trace amounts of oil droplets suspended in the air that flows through the valve. These droplets keep the valve lubricated. I would bet that a majority of forklift dealerships do not change PCV valves on routine preventative maintenance and experience problems because of this.

By following these simple steps your service department can avoid engine and customer relation problems. It is our job as forklift professionals to stay on top of maintenance related items for our customer’s equipment and this article should have helped.

If you have any questions regarding this article or any other Tech Talk article please feel free to give me a call @ 877/303-LIFT (5438). As always, stay tuned to future helpful Tech Talk articles!