The purpose of the CDR valve is to maintain 0 to 4 inches of water vacuum in the crankcase at all engine speeds, assuming that the piston/ring combustion blow by is not excessive (less than 4 cfm). Too little vacuum will tend to force oil leaks.

The CDR valve is checked with a water manometer. The U-tube manometer indicates pressure or vacuum by the difference in the height of the two columns of the fluid.

If the crankcase vacuum is greater than 0.996 kPa (4 inches of water), dirt or dust can more than likely be pulled into the crankcase cavity (pulled through front/rear crankcase seal, etc...) and contaminate the oil. If the crankcase pressure is positive, engine oil leaks are more than likely to occur around the engine seals and the gaskets.

1. Connect one end of the manometer to the engine oil dipstick hole. The other end of the manometer is vented to the atmosphere.
2. Unplug the rubber vent tube from the turbo inlet elbow.
3. Run the engine through a no-load speed range (gear selector in PARK) and the observe manometer readings. If the manometer reading is +0.996 kPa (+4 inches of water) or less positive pressure, reconnect the CDR system and proceed to step 4. If the manometer reading is higher than +0.996 kPa (+4 inches of water) positive pressure, this indicates that there is an internal engine problem.
4. Install the air cleaner.
5. Start the engine and observe the manometer reading. The manometer (vacuum) reading should read +0.249 kPa (+1 inches of water) at the idle to approximately 0.747-1.25 kPa (3-5 inches of water) at 2000 RPM. Add the amount that the manometer column travels up, to the amount that the column travels down in order to obtain the total water pressure (vacuum).