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.
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).