Crankcase Pressure Check

TOOLS REQUIRED:  SA9127E Gauge Bar Set

High crankcase pressure indicates an excessive amount of air passing between the rings and cylinder walls into the crankcase. A loss of engine lubricating oil into the air intake tube/filter housing or out the dipstick hole is indicative of excessive crankcase pressure. High negative pressure or vacuum can be caused by a plugged air filter element or restricted air intake.

Test method: 

1. Remove the dipstick and connect a 0-15 kPa gauge (0-16 in. H₂ O manometer or magnahelix in Gauge Bar Set SA9127E) to the dipstick tube.
   Fig 1: Connecting Gauge Bar Set To Dipstick Tube

   Courtesy of GENERAL MOTORS CORP.
2. Operate the engine until it reaches normal operating temperature and observe the crankcase pressure with engine at 4000 RPM.
3. The crankcase pressure should not exceed:

   Crankcase Pressure (New Engine): 

   1. Positive:  1.0 kPa (4.0 in.) H₂ O Max.
   2. Negative:  3.0 kPa (12.0 in.) H₂ O Max.

   Crankcase Pressure (Used Engine): 

   1. Positive:  2.5 kPa (10.0 in.) H₂ O Max.
   2. Negative:  3.5 kPa (14.0 in.) H₂ O Max.

4. If the crankcase pressure exceeds specifications, ensure the PCV system is functioning properly.
   NOTE: It may be necessary to complete a compression and cylinder leakage check for evaluation of piston rings and cylinder walls when there is high (positive) crankcase pressure. Low (negative) crankcase pressure indicates a possible restricted air intake system.