Crankcase Breather
Gases formed in the crankcase are directed to the intake manifold. Harmful vapors that would otherwise collect in the crankcase and contaminate the oil, or escape to the outside, are drawn back into the engine and burned.
The crankcase breather is located in the valve cover. A restrictor is cast into the fitting for the breather hose on the intake manifold. The restrictor limits the flow of gases from the crankcase to the intake manifold and keeps the crankcase pressure from getting too low in vacuum. A breather hose connects the crankcase breather to the intake manifold.
Crankcase Breather
| 1. | Breather Hose | 5. | Baffle Breather |
| 2. | Insulation | 6. | Baffle Plate |
| 3. | Breather Cover | 7. | Intake Manifold |
| 4. | O-Ring | 8. | Restrictor Location |
Normal crankcase pressures with a new air cleaner are 0 to 300 mm (0 to 12 in.) H2O of vacuum. The vacuum will increase as the air cleaner gets dirty and becomes more restrictive. Check the air restriction indicator before checking the crankcase pressure. Replace the air cleaner if the reading on the air restriction indicator exceeds 508 mm (20 in.) H2O of vacuum. A dirty air cleaner may cause excessive vacuum, leading to oil carry over and high oil consumption.
The crankcase breather and the breather hose should be inspected when the air cleaner element is replaced to verify they are not plugged or damaged. Inspect the insulation to verify it is in place and undamaged. The insulation is used to prevent freezing in cold weather.
The following items can affect the crankcase pressure readings:
| Crankcase Pressure Effect | Typical Cause |
|---|---|
| Increase | Piston Rings Stuck or Worn |
| Increase | Breather Hose or Restrictor Plugged with Dirt or Ice |
| Decrease | Air Cleaner Dirty or Plugged |