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 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 fluid.

If the crankcase vacuum is too high (greater than 4 in. water), dirt or dust can more 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 likely to occur around engine seals and 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 turbo inlet elbow.
3. Run engine through no-load speed range (gear selector in park) and observe manometer readings. If manometer reading is +4 in. water or less positive pressure, reconnect CDR system and proceed to step 4. If manometer reading is higher than +4 in. water positive pressure.
4. Install the air cleaner.
5. Start engine and observe manometer reading. It should read zero to one inch (0 to 1 in.) of water (vacuum) at idle to approximately -3 to -5 inches of water (vacuum) at 2000 RPM. Add the amount that the manometer column travels up, to the amount that the column travels down to obtain total water pressure (vacuum). An example of a manometer reading is as follows: One-half inch above zero plus one-half inch below zero equals one inch vacuum reading (1/2 in. +1/2 in. =1 in.).