Volvo Coupes/Sedans/Wagons 1970-1989 Repair Guide

Positive Crankcase Ventilation (PCV) System

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OPERATION



Blow-by gasses, combustion gasses that squeeze past the piston rings, tend to collect in the bottom of the engine and, if not vented, will build pressure inside the crankcase until they force their way out. These gasses usually exit through a gasket or an oil seal, creating an oil leak. On older cars, a simple breather pipe was used to vent the blow-by gasses into the atmosphere. This method cannot be used today because blow-by gasses are air pollutants.

On all of the Volvos covered in this guide, a PCV system is used which routes the blow-by gasses into the air cleaner or intake manifold where they are burned with the air/fuel mixture.

SERVICING THE PCV SYSTEM



See Figures 1 through 10

Although the gasses build up at the bottom of the engine, the pressure is distributed throughout the inside of the engine. It is easiest to vent them at the top of the engine and conduct them back to the air intake system. For this reason, look for the hoses which run to the valve cover(s) on top of the engine. They are usually found close to the oil filler cap.



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Fig. Fig. 1: Cutaway view of the common PCV system-B20B engine shown



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Fig. Fig. 2: Dual PCV valves and hose routing-B27F engine shown, B28F engine similar



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Fig. Fig. 3: Crankcase ventilation system-B27F, B28F and B280F engines



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Fig. Fig. 4: Diesel PCV systems-upper: D24 engine; lower: D24T engine



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Fig. Fig. 5: PCV system hose routing-B280F engine



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Fig. Fig. 6: Cutaway view of the crankcase ventilation system-B21, B23 and B230 engines



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Fig. Fig. 7: PCV system-B21F engines



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Fig. Fig. 8: PCV system-B230F engine



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Fig. Fig. 9: PCV system-B230F turbo engine



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Fig. Fig. 10: Exploded view of the PCV system-B21FT engines

Carefully remove the hoses from their fittings one at a time. You are dealing with plastic and/or rubber hoses which have been subjected to engine heat and fumes; they may be brittle or stuck in place. Make sure all hoses and PCV valve nipples are clean and not damaged. Check hoses for blockage and make sure the flame protector, found on some cars after 1983, is not blocked. Replace any torn or disintegrating hoses with heat treated, preferably factory replacement, hose. The PCV nipple(s) in the intake manifold, the flame guard and the oil trap should be removed and cleaned every 12,000-15,000 miles (19,324-24,155 km) on cars so equipped. The PCV nipple may need replacement at 60,000 miles (96,618 km).

 
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