PCV SYSTEMS: MAINTAINING THE FLOW BY SAM BELL Like other well-established technologies, PCV systems can be taken for granted. But PCV faults can cause a wide range of driveability symptoms, as well as oil consumption and/or leakage problems.

arly internal combus- matter how well-built, contributed their tion engines, like the share of this type of pollution. steam engines which Road-draft tubes were an early at- preceded them, were tempt to cope with the increased messy and smelly con- pressures that accompanied traptions. They routine- ever-higher engine speeds and loads. ly leaked oil and spewed noxious fumes These tubes were fitted onto the tops of Einto the atmosphere. Many features we the engines, extending up several inches this advance in engine design, crankcase now take for granted were missing, in- before looping down to an open end fumes still accounted for nearly half of a cluding, in many cases, even valve cov- positioned somewhere in the “draft” or typical engine’s hydrocarbon emissions ers and seals! Early “engi- relative low-pressure area beneath a and were a major factor in the forma- neers” often subscribed to the belief moving vehicle. The pressure differen- tion of sludge (see the sidebar on page that oil leaks simply assured a full flow tial between the two ends of the tube 36) and the breakdown of engine oil. of lubrication to the bearings. Gaskets allowed the relatively pressurized During the economic boom that fol- and seals, as anyone who grew up ser- crankcase gases to flow downward into lowed the end of World War II, an ever- vicing English knows, were meant the vehicle’s slipstream. The short up- burgeoning vehicle population, coupled simply to limit oil loss, not prevent it. ward section of the tube kept the heavi- with increasing urban growth and heavy Blowby gases, including substantial est oil droplets from following along industrial emissions, led to increasing quantities of water, escaping past the with the flow. Breathers of one sort or smog formation in many areas of the rings would diffuse through the another had to accompany the draft country. Testing and analysis eventually engine oil and escape into the atmos- tube to allow makeup air to flow into confirmed that automotive crankcase phere. Worn or poorly built motors the engine. These were often simple fumes were also a significant contributor, spewed more of these hydrocarbon- mesh openings integrated into oil filler and support for industry regulation grew. laden fumes, but all early engines, no caps or air cleaner housings. Even with As it happened, an existing technologi-

30 August 2013 are produced in varying amounts under different operating conditions. At idle, when manifold vacuum levels are high and loads are low, crankcase fumes are at a relative minimum. Under these conditions, the high vacuum sucks the restrictor to nearly close the valve. Makeup air is supplied to the crankcase via a breather hose, “positively” displac- ing the crankcase fumes—hence the cheery “positive” of the PCV name. Under midrange openings, engine loads and speeds are higher, and more blowby gases are produced. Man- ifold vacuum, however, is lower, so the spring tension can largely counterbal- ance the pressure differential, thus al- lowing increased flow through the valve. As before, the breather supplies clean air to displace the fumes. At very high throttle openings, intake manifold vacuum drops to near zero. Spring tension then holds the valve open for maximum flow, just as it does with the engine off. Even so, the amount of blowby gases needing evacu- ation often exceeds the flow capacity under high-load conditions. At such times, a substantial portion of crankcase gases may flow backwards from the en- gine through the breather and into the housing or intake snorkel. (This accounts for all those oily breather filter elements we changed back in the not- so-good old days of carburetion.) Some vehicle designs opt for a fixed- orifice PCV system. Here, there are no moving restrictor pellets and no springs, but simply an opening con- necting the crankcase to the intake Photo: Sam Bell Photo: manifold. Such systems usually incor- cal solution to the problem had been de- How It Works porate an oil separator. veloped for a somewhat different appli- The photo on page 34 (top left) shows a Separation anxiety, as I like to call it, cation during the war. This was the PCV cutaway view of a typical PCV valve. has led some manufacturers to opt for (positive crankcase ventilation) valve, The larger end is typically fitted into a more complex PCV system designs incor- originally developed to prevent water grommet, often located in a valve cover, porating oil separators, whether coupled from traveling back into the road-draft through which the blowby gases will be with a conventional PCV system or with a tubes of tanks fording rivers and streams. evacuated for introduction into a central fixed-orifice system. Oil loss is an ongoing Eventually, engineers at GM’s Cadil- location in the intake plenum. Each end problem for many PCV systems, and lac Division, which had built Army of the valve features a carefully sized such separators are a logical means of tanks during WWII, adapted the PCV orifice, with a tapered pellet riding be- combating it. Most consist of a molded valve to automotive use, supplanting the tween. A precisely calibrated spring acts plastic container with one or more inter- recombustion tube. Through the Auto- to help regulate the flow as speeds and nal baffles. They’re usually attached at mobile Manufacturers Association, GM loads change. Obviously, any change in the lower end directly to the block via an offered the technology, royalty free, to orifice size, pellet weight, spring tension externally sealed tube positioned well all U.S. automakers. It was quickly or mounting orientation can alter the above the normal oil level. The upper adopted by all, just a year ahead of valve’s performance characteristics. end of the separator assembly may be fit- scheduled requirements. As you might expect, blowby gases ted directly to the PCV valve or plumbed

August 2013 31 PCV SYSTEMS: MAINTAINING THE FLOW

that bypasses the via the crankcase. If the breather hose is located downstream of the MAF sensor, throttle valve deposits are again likely. In either event, if the breather configu- ration has been altered relative to the MAF sensor, a new fuel map will need to be programmed in. Manufacturers and aftermarket suppli- ers have tried a number of solutions, with mixed success. One of the most interest- ing adaptations is the Krank Vent Crank Case Vacuum System, available at http:// www.et-performance.com/turbo.html. This approach uses two additional check valves plumbed into the PCV and Photos: Sam Bell Photos: breather system hoses and claims to pro- This dismantled Saturn PCV valve typi- duce and maintain a vacuum in the fies conventional valve construction. The crankcase. Other designs may make use smaller port (upper right) is connected to intake manifold vacuum, which tries of heated separators, fixed orifices or I drew a grid on this shop towel to high- to suck the tapered pellet (lower left) to even dual-stage ventilation valves. light the standing center pressure wave an almost-closed position at idle. As Flow rate through an orifice is pro- and surrounding “donut” depression manifold vacuum drops, the precisely portional to the size of the restrictor and typifying normal PCV operation on a calibrated spring (center) counterbal- the pressure differential between the Corolla engine. Try the experiment de- ances the effect of the vacuum, opening two ends. The actual flow rate can be scribed in the text so you can see how the valve to allow more flow. measured in liters per minute at a speci- the system reacts to altered conditions. fied pressure drop, but as technicians to it. Some manufacturers utilize a fixed- we’re usually more comfortable think- I discovered that PCV flow at idle can orifice restrictor instead of or in addition ing in the more familiar terms of grams account for upwards of 10% of total to a conventional variable-flow valve. Any per minute (gm/min.). flow, while at 2000 to 3000 rpm it might oil droplets incorporated into PCV flow I set out to make a few rudimentary account for a greater mass but a smaller eventually wind up as soot particles that measurements by monitoring MAF flow percentage of total flow. can foul exhaust oxygen or air/fuel sensors rate at idle with the PCV system in nor- Many PCV systems will last the life of or degrade substrates. mal operation, then with both the PCV the vehicle with no need for special atten- Of course, adding a turbo or super- hose and the breather hose temporarily tion. Tiny oil droplets suspended in the charger complicates the engineering blocked off. On a representative 2.0L crankcase usually keep the spring and considerably. Under boost, the pressure engine, the MAF rate dropped from pellet clean and lubricated. Sticky PCV in the intake manifold may easily exceed 2.26 to 2.05 gm/sec. with the ventilation valves usually indicate a lack of regular oil that of the crankcase, effectively stopping flow blocked. Using this and other data, changes. Gummed-up PCV valves may normal-direction PCV flow result in poor or unstable idle just when load and blowby or excessive fuel trim correc- gas production are at their tions. (These trim corrections peak. The rapidly increased can be in either direction, de- pressure within the crankcase pending on whether the valve under boost may blow heavily is sticking in a more open or oily fumes through the more closed position than ex- breather and into the intake pected.) Insufficient flow may snorkel or the airbox. If the result in MAF sensor contami- breather is located upstream nation or oil leaks. Oil accu- of the MAF sensor, oil conta- mulation in tubes mination and excessive throt- often signals a fault—usually tle deposits likely will result. insufficient flow—somewhere Modifications to the facto- in the PCV system. ry turbo can also cause sig- Excessive flow rates can nificant rich running, as cause stalling, high idle or stock software algorithms This hard-to-see heater tube loop, wrapped around the unacceptable fuel trim cor- meter fuel to match the air breather hose, plays a big role in reducing sludge formation. rections. Internal oil con-

34 August 2013 PCV SYSTEMS: MAINTAINING THE FLOW

The split hose on this Mazda5 caused a lean running condi- tion. This is one instance where you may have to break out To test the PVC system, attach a vacuum gauge to the oil the smoke machine. That’s the oil separator behind it, with dipstick. (A spark plug boot makes a dandy adapter!) Let the gridlike surface. The intake manifold in its installed po- the system stabilize, then read vacuum. Now pinch the sition thoroughly hides both from view. Even a flexible breather hose shut and watch the gauge. Start by checking borescope has a hard time with placements like this. known-good vehicles to build a library of normal data. sumption can also result. I once fixed a ber hoses for connections to the intake crankcase fumes containing both water Toyota that idled at 35 mph in gear sim- and one or more additional breather and volatile organic compounds. Histor- ply by installing the correct PCV valve. hoses. These hoses must be resistant to ically, such hoses feature multilayer, re- In my experience, the vast majority of degradation from exposure to oil and inforced construction. Some OEMs flow rate problems stem from incorrectly calibrated PCV valves. Consider this: OE valve suppliers may catalog as many as Sludge! 750 part numbers. Your local fast-lube ears of advertising have ac- joint may carry as few as a dozen or two. burned hydrocarbons. The relatively quainted all of us with sludge, cooler crankcase surfaces promote To further complicate matters, as Mark Ythe scourge of all . their condensation, as does the Sarlo, an automotive, principal research Or has it? No one I asked could actu- pumping action of the undersides of engineer who now runs Tri-State Diag- ally explain the formation or compo- the . Once they’re allowed to nostics in La Junta, CO, remarks, “One of sition of oil sludge, though all drip into the oil pan, the swirling the lubricant tests run needed OEM PCV agreed that it was a bad thing for a flows induced by the oil pump en- valves that flowed according to spec. We vehicle. So, what is sludge? How sure that these compounds mix thor- built a test rig, tested PCV valves to assure does it form? What’s so bad about oughly with the rest of the lube. they met the OEM design specs....OEM it? Can it be prevented? A pressurized film of long chain oil Let’s tackle these questions in or- molecules makes a good lubricant PCV valves had an 88% failure rate. That der. At the simplest level, sludge is a is correct, only one out of eight was in that can be pressurized to produce a mixture of oil and water, often ac- film to separate metal components spec (we had wooden crates full of PCV companied by various other com- moving at high relative speeds. Wa- valves that didn’t pass OEM specs). On a pounds. The water is a byproduct of ter alters both viscosity and film humorous note, we tested different after- combustion. In the complete com- strength adversely, resulting in in- market PCV valves (which most often are bustion of gasoline, all of the hy- creased engine wear. To further exac- ‘reverse engineered’). Just think, an after- drogen is ideally converted to water erbate the situation, the carbon diox- market company buys 10 OEM PCV in substantial volumes. Most of the ide (CO2) and the various additional valves, flows them, measures their dimen- water exits via the exhaust, some of hydrocarbons combine with the wa- sions, then builds an aftermarket PCV it accounting for the liquid you see ter to produce an acidic soup which dripping from a cold tailpipe in the promotes even more engine wear. valve.... So now we have an aftermarket morning. valve built on an average of OEM valves Prevention, to the extent feasi- A portion of this water, however, ble, is accomplished by introducing that might not be in spec. The fabrication enters the crankcase as a compo- a flow of fresh, outside air via a tolerances of the aftermarket valve may nent of the blowby gases that find vent tube, then applying a vacuum, put it so far out, who knows what the en- their way through the end-gaps of usually at an upper location like a gine will end up with. I have ‘treated’ a the piston rings, primarily during the valve cover, to induce these gases to few engines with oil consumption prob- power . Accompanying the flow out of the crankcase before lems just by installing OEM PCV valves” water into the crankcase are they can condense. The PCV valve [emphasis added]. burned, unburned and partially controls the flow rate. Most PCV systems incorporate rub-

36 August 2013 PCV SYSTEMS: MAINTAINING THE FLOW have used thinner, less ro- for smaller leaks or incorrect bust materials which can col- flow rates. lapse, suck closed or split Finally, a number of manu- over time. When inspecting facturers have turned to heat- PCV operation, always look ed PCV systems or valves. for signs of these problems, Several Honda models from which, if present, are usually the ’90s feature a coolant tube visually or audibly evident on in direct contact with a closed-throttle decel after a breather tube pipe to allow snap-throttle check. heat transfer to the incoming Some PCV systems fea- breather makeup air, thus re- ture separate flame traps or ducing internal condensation. spark arresters. As the Some later versions feature a names suggest, these are in- loop of engine coolant flowing tended to prevent an intake The varnish pattern on the underside of the baffle plate on through a tube surrounding backfire from causing the this Ford Escort valve cover reveals the thermal pattern of the PCV valve, or they may hydrocarbon-laden the hidden flow paths. Brighter areas correspond to cold rely on an integrated electrical crankcase fumes being set spots where hot PCV gases first condense. Heavily var- heater element. nished areas indicate hot spots. Note the relative cleanli- on fire or, worse, exploding. ness of the left side, where clean air enters via the Originally developed to A typical flame trap is made breather, in contrast to the right side, where the PCV gases combat throttle icing in a few from a coil of corrugated exit via the PCV valve. The vertical divider above the oil fill isolated applications, heated sheet metal wound into a opening prevents the breather air from flowing directly to PCV systems were soon rec- disc shape. These flame the PCV valve, located at the bottom right. ognized for their far greater traps do require occasional impact in reducing acid and maintenance or replacement. (The ven- duct or hose with the idea that a total sludge formation. Their widespread erable Ford 5.0L engine was renowned failure in the form of a detached hose adoption, coupled with advances in oil for oil-contaminated MAF sensor prob- would cause either a stalling condition chemistry, has been a major factor in al- lems, ultimately traceable to plugged ar- or a major shift in fuel trim. This strate- lowing greatly extended oil-drain inter- resters rather inconveniently located to- gy has been implemented successfully, vals. They have also allowed manufac- ward the very back of the motor under though it fails to monitor directly either turers to breathe a little easier as they the cowl area. A similar problem was widespread on many Volvos as well. Oil separators are susceptible to seal Bringing the Heat leakage as thermal cycling ages O-rings or as internal ports and passages become hy on earth would you however, could allow significant clogged. Many VW/ products fea- want to heat a vehicle’s gelling of the water and oil mixture, ture a diaphragm built into the valve cov- WPCV system? Throttle icing creating a breeding ground for was never widespread, although sludge. In sufficient quantity, this er. Dorman Products offers an aftermar- every occurrence carried with it the ket alternative, allowing technicians to gelled sludge can substantially re- obvious potential for significant le- duce PCV flow rates, significantly re- replace just the diaphragm, which is not gal liability. Traditionally, the engi- ducing PCV performance. otherwise sold separately. neering path of least resistance was Burning a gallon of gasoline pro- Various PCV faults can also cause to build a complex series of baffles duces about a gallon of water. This some more surprising symptoms, includ- (usually in the valve cover) featuring water, once allowed to condense ing high-pitched whistling noises which “coalescers” where moisture would from its state as superheated steam, may seem to come from the timing cover condense out of the PCV flow rapidly joins with other blowby gases or bellhousing areas. These usually signal stream before being introduced into to form acidic compounds which de- a broken or missing PCV valve, which al- the intake plenum of a cold engine plete the acid-fighting additives in where the expansion of incoming motor oil. Heating the PCV valve (or lows too much vacuum in the crankcase. air around the throttle plate might The noises are air being sucked into the its associated plumbing) reduces the condense and freeze it. Later, as the amount of water condensation from motor past one or more seals. engine warmed up, these cool spots the blowby gases, thus further reduc- would reach a normal operating ing sludge formation while extend- Latest Developments temperature—typically somewhere ing oil life. Even so, a vehicle that PCV monitoring began in earnest in above 160° to 180°F. The accumulat- does nothing but short trips will still 2002 models, usually as part of the ed moisture would then evaporate require more frequent oil changes OBD II Fuel Monitor. Some manufac- into the continuing flow. and the occasional long haul to bake turers choose to route PCV flow Short-trip operating conditions, out the accumulated moisture. through an extremely high-diameter

38 August 2013 PCV SYSTEMS: MAINTAINING THE FLOW face mandatory extensions of catalytic how it affected the rag’s behavior. With on multibank vehicles, are routed at the converter warranties (see “Bringing the no vacuum to the PCV valve, the rela- rear of the engine compartment. Over Heat” on page 38). tive heights of the upper and lower por- the years, I’ve found many of these which One of the simplest tests is one we tions of the standing wave changed, inadvertently had been left disconnected perform routinely at my shop with most with the upper area growing higher and following routine air filter replacement. A oil change services. After pouring in the the lower area no longer being so low. smoke machine may help pinpoint leaks fresh lube, put a shop towel over the oil Do the experiment yourself on several in areas that are hard to reach. fill hole—or, better yet, over a funnel vehicles so you’ll know what to look for. When insufficient flow is suspected, that fits it well—and take a look as you The practical question is how and my first test is to remove the oil dipstick start the engine to fill the . The when to actually test the system if you and install a vacuum gauge on the dip- rag’s behavior will usually involve a flut- suspect a problem. Again, it pays to start stick tube. Allow the engine to run at an ter, in some instances producing a stand- by checking known-good vehicles. Start idle for a minute or two until the read- ing wave, where one area is slightly lower with a newer, well-maintained vehicle ing stabilizes. Depending on the model, and another slightly higher, with the en- with no history of unusual oil consump- you should expect to see either no vacu- tire surface vibrating lightly. A few en- tion or driveability problems. Your first um or only a couple of inches. Any posi- gines with more robust PCV valving may test should be a simple visual inspection tive pressure reading indicates a serious suck the rag inward pretty deeply. Again, to determine whether all necessary com- problem. Next, block off the breather experience quickly acclimates you to nor- ponents of the system are present, intact hose. You should see vacuum begin to mal for the models you see regularly. and properly connected. Look for col- register pretty quickly at idle. As an experiment, I blocked off the lapsed hoses by performing a snap-throt- Experience is a good teacher here. PCV hose on a couple of vehicles to see tle decel. Many breather hoses, especially How much vacuum and how quickly it builds can tell you a lot. Low vacuum may signal restrictions within the PCV valve or plumbing, a leaky valve cover gasket or excessive blowby. A hard vacu- um that builds up very quickly to match the intake may signal an incorrectly cali- brated valve or one that’s stuck wide open. Most healthy systems fall some- where in between. A pressure buildup during this test indicates an inoperative system or an engine with severe blowby problems. If the pressure drops when the breather is allowed to open, then you know that side of the plumbing is at least not fully restricted. Conclusion Like many well-established fundamental technologies, PCV systems are often tak- en for granted. Most are robust enough to tolerate benign neglect, but a few re- quire active maintenance. Correct PCV function and flow are essential to oil life and catalytic converter longevity. PCV faults can cause a wide range of driveability symptoms as well as oil con- sumption and/or leakage problems. Ba- sic functional testing is relatively easy, but a library of known-good values and behaviors is essential to successful diag- nosis, especially when the issue is one of calibration rather than total failure. Top photo: Stripes and chevrons indicate baffle openings. The “smiles” (near the left upper corner and vertically above the breather nipple, center left) indicate small- This article can be found online at diameter equalizer tubes. The gasketed baffle plate is held perpendicular to Above: www.motormagazine.com. the cover, exposing an intricate flow path. The PCV valve is at the upper left side.

40 August 2013